[Tomnavigator]

lnxguy and E.Murray Thanks for your comments. I spent a year trying to find out what is causing my a/c issue. I can't stand it any longer and am giving up on finding out why. Now I just want the a/c to work. I have heard from a couple of people who have the same problem I have with the a/c not working for a few minutes after the car is started. Here is what we have in common
1) It only happens when the car is first started after sitting overnight or for a few days.
2) The air comes out of the air registers like the a/c is running but the air temp is hot.
3) It does not matter how many time you turn on or off the a/c it takes about 3 to 5 minutes for the a/c to start working.
4) It does not matter what temperature you select 65, 70, 75, etc. the a/c takes the same time to start working.
5) It does not matter if you start the car with the a/c turned off or with a/c turned on. The a/c still takes the same time to start working.
6) You can sit in your driveway for a couple of minutes or immediately drive off. The a/c starts working approximately 3 to 5 minutes after the car was started.
7) Putting the car on "MAX" a/c does not change anything. It still takes 3 to 5 minutes.

What I think is that it is something that BMW programmed into the car to cheat emissions testing or get improved fuel mileage rating when the car is tested by the government like Volkswagen did with diesel gate. Germany has announced that it found that BMW and Mercedes colluded with VW to cheat the emissions testing. I think, the computer program is supposed to sense when it is being tested and the a/c is turned off. Somehow our cars think the car is being tested and turns off the a/c to improve fuel mileage and/or emissions. After about 5 minutes the car decides the car is not being tested and allows the a/c to turn on. I guess I am suspicious. But, noone here has been able to help with this problem and there are several very knowledgable people on this forum such as BB_cuda, kbsilver, and 335dici to name a few that have not been able to come up with a cause/fix in the last year.

[Tomnavigator]

Please help with the following so I can try to fix my a/c issue.
1) Can someone confirm that the 335D air conditioner variable compressor is controlled by a pulse with modulator signal from the computer? If so, is it a 12 volt signal or a ground signal?
If the compressor is controlled by a pulse width modulator signal either 12 volt or grounded signal, Then it probably has 2 or 3 wires going to the solenoid that controls the compressor output. One would be a control wire, one would be a feedback wire and the third would be a permanent ground wire or switched 12v supply wire. Could someone with a wiring diagram look up the wires to the a/c compressor and let me know the wire colors and where the wiring diagram shows they come from so I can try a work around fix.
I plan to purchase a pulse width modulator and use it to turn on my a/c when the car is first started. I am going to also get a 5 to 7 minute timer circuit to turn off the pulse width modulator after about 5 minutes so the car's computer can control the a/c the rest of the time.

[Tomnavigator]

This post does not relate to my problem so only read this if you wonder why we have variable output a/c compressors instead of an a/c compressor with a clutch and you want to know the difference.

First an a/c compressor with a clutch. The clutch turns on and off the compressor as needed. When the compressor is on it is outputting at 100 % when off the compressor outputs 0 %. Your a/c compressor would be turned on many times each hour as you drive your vehicle. This is relatively inefficient and why variable output compressors were built.

A variable output a/c compressor runs all the time and the output is controlled by a solenoid valve that can vary the compressor output from 0 to 100 % and anywhere in between. On very hot days or when you start your car when it has been sitting in the sun the compressor is putting out 100%. As your car cools down, the compressor output is reduced an may only be putting out 30 or 40 % on cooler days or overcast days. This is more efficient and provides a constant load on your car engine.
One advantage of the variable output compressor is that it can easily be turned off during times of high acceleration to allow more engine power to be used to accelerate your car instead of being used to cool your car.
A second advantage is that the load on your car engine stays more constant instead of the load being turned on and off and on and off like a clutched a/c compressor does. This improves MPG.

[BB_cuda]

Originally Posted by lnxguy

There's gotta be a reason why the AC isn't kicking on. Any outstanding errors/codes?

I agree. The DDE (what we call the ECU) is what controls the application of power to compressor. I wonder if a reload of DDE might help this. Perhaps this is one of the boxes Tomnavigator has already checked.

Tom, in subsequent entries, you speak to using 100% duty cycle. I'm a little worried this might freeze things up either at the orifice (that's where liquid flashes to mix of liquid+ gas, constant enthalpy process) or down stream in the evaporator. I'd be real careful here. My last entry was a suggestion to measure the voltage but you have since learned its 12 v and a varying pulse width modulation.

I do wonder if the DDE will get upset by you taking its control away and forcing the compressor on?

[lnxguy]

You really need to see some live data when the car is first started. The AC won't kick on if certain criteria isn't met. The fact that it turns on after a few mins of driving makes me think you've got air or something in the system. Have you had a professional look at this? It might be time to get another set of eyes on it before trying to bypass or use a workaround.. I'd take it to an AC shop and get a complete system check done. Then you know 100% you have no leaks, aren't low on refrigerant, etc.

Some good info in this thread, seems like a very similar situation. Check out post #12.

https://www.e90post.com/forums/showthread.php?t=1627650

[Tomnavigator]

lnxguy - Sorry about the delay in replying to your questions. For a year I have looked for a reason and noone can come up with a reason. There are no codes current or historical. The a/c compressor just does not come on for 3 to five minutes. During this time the air temp in the car can be over 120. Once the a/c compressor kicks in, the a/c works as it should until the car sits overnight. If I start and stop the engine multiple times during the day, the only time it will not work properly is the first start up of the day. BMW does some weird things in the name of getting better fuel mileage. Some BMWs only charge the battery when the car is coasting. If you are accelerating, running at a steady speed or sitting still, the car will not charge the battery. Many BMW cars are programmed to turn off the a/c compressor and not charge the battery during hard acceleration to allow the maximum amount of power to be used to accelerate the car. It could be possible that there is some programming in the engine control computer that turns off the a/c compressor and/or the alternator, if the car thinks it is being tested for emissions or fuel mileage. All I know is that I have been trying to resolve this problem of no a/c for over a year and nobody here can come up with a reason why my a/c does not work for 3 to 5 minutes after the vehicle sits overnight.

[Tomnavigator]

Lnxguy. I have done all my vehicle a/c work for the last 50 years. I pulled a vacuum on the system with my a/c vacuum pump and refilled the system with freon. I know there is no air in the system and the freon charge is correct. I agree that something is causing the a/c to not turn on. I just can not find out what it is. I have found out over the last year that there is a handful of people on here that have the same issue with their cars. Just nobody has ever been able to fix it yet.

[Tomnavigator]

BB_Cuda - You may be right about needing to reload the DDE program. However I have some programming in my DDE that I do not want to lose. For this reason, I am reluctant to reload the DDE programming.
I ordered a pulse width modulator for my intended work around. I also agree with you that when I install it I do not want the output to be 100%. I will probably start with 90% to make sure I don't hurt something. a/c compressors are expensive.. The timer circuit I ordered will power the pulse width modulator to entergize the a/c compressor for 4 minutes one time only upon startup. I will also install a relay to disconnect the a/c compressor input from the DDE when the compressor is being entergized by my pulse width modulator to make sure there is no feedback issues. I don't want to fry my DDE either. It will be a few weeks before I get my pulse width modulator and timer circuit. And I still need to get information on the wiring diagram for the a/c compressor activation solenoid.
The timer circuit I ordered uses a trigger signal to activate it. I will install a momentary contact switch in my car and press the button to activate the a/c compressor. This way the setup will be manually activated my me and I can activate it the first time I start the car in hot weather. I don't really want this setup to automatically activate the a/c every time I start the car all year long. I just want the circuit to activate the a/c the first time the car is started each day during hot months. I want the DDE to control the a/c the second, third, etc time I start the car each day and in the winter.

[604x5]

Seems like a rather unnecessary work around to fix an issue that is not present in every other 335d. Have you done any data logs and compared readings when issue occurs VS when it doesn't occur. I would be looking for conditions that would prevent compressor operation and compare your readings to those.

[Tomnavigator]

604X5 I see you are from Vancouver and I understand why you don't understand why I want to do an "unnecessary work around" to get my a/c working. I invite you to come down to Louisiana where there is 100 % humidity and sit in my car with an interior temperature of 120 degrees for five minutes. I promise you that you will understand why I am willing to do the work around.
I don't have access to BMW programming code to know what parameters are used to turn on the a/c compressor. All vehicle air conditioning systems use multiple sensors, temperature sensors, pressure sensors, sunlight loading sensors, voltage sensors, etc. to determine when and how much to turn on the a/c compressor. BMW keeps the a/c compressor off when the voltage of the battery is too low. The a/c compressor could be kept off by the computer because of emissions, or because the engine coolant is not up to temperature, or the heat load module is not giving a good signal, or a transister in the control module is weak and has to be on for a few minutes before it can control right or the car thinks the battery voltage is too low, or the car thinks I want to accelerate too fast so it is keeping the a/c off to help car accelleration or numerous other things. There is no engine trouble code fault. The computer is just not turning on the a/c.

After a year of suffering, I want the pain to end. There are a few other people with my same problem. Their a/c won't work for the first few minutes. Then works fine and cools like it should for the rest of the day. No one has been able to figure out why the a/c won't work. I do not know all the parameters the a/c module looks at and the programming logic used to turn on the a/c compressor so I think logging everything would be a pointless exercise. I have wasted way over twenty hours looking for the reason, buying, replacing, and registering a new battery, removing the freon, pulling a vacuum on my a/c system and recharging the system, etc. If I can bypass the a/c module and get the a/c working then that is all that matters to me.

I view this like It is like having diarrhea, I don't need to know where I got it or what is causing it. I just need to know how to treat it and what to do to get over it so I can feel better. My work around will cost me about $25 and can be implemented in about an hour and I am almost certain that it will work.

[BB_cuda]

Originally Posted by Tomnavigator

BB_Cuda - You may be right about needing to reload the DDE program. However I have some programming in my DDE that I do not want to lose. For this reason, I am reluctant to reload the DDE programming.
I ordered a pulse width modulator for my intended work around. I also agree with you that when I install it I do not want the output to be 100%. I will probably start with 90% to make sure I don't hurt something. a/c compressors are expensive.. The timer circuit I ordered will power the pulse width modulator to entergize the a/c compressor for 4 minutes one time only upon startup. I will also install a relay to disconnect the a/c compressor input from the DDE when the compressor is being entergized by my pulse width modulator to make sure there is no feedback issues. I don't want to fry my DDE either. It will be a few weeks before I get my pulse width modulator and timer circuit. And I still need to get information on the wiring diagram for the a/c compressor activation solenoid.
The timer circuit I ordered uses a trigger signal to activate it. I will install a momentary contact switch in my car and press the button to activate the a/c compressor. This way the setup will be manually activated my me and I can activate it the first time I start the car in hot weather. I don't really want this setup to automatically activate the a/c every time I start the car all year long. I just want the circuit to activate the a/c the first time the car is started each day during hot months. I want the DDE to control the a/c the second, third, etc time I start the car each day and in the winter.

I get the point of not wanting to have your DDE over written. Been there anf had dealer write over my JR 2.8 tune. I sent it back to Georgia for a free reload of my tune (thanks Andrew!).

I read your response to 604x5. This provoked some ideas. You state there are lots of sensors that ECU looks at to decide to activate compressor or not. I can see that you are an ex A/C pro based on answer to another poster of having many years of experience. My dad was same kind a guy with an A/C and refrigeration license in state of Texas. I gotta say dad would know nothing of fancy BMW programming and whether outside temp sensor had to communicate with ECU, solar sensor same, other sensors that I may know nothing of.

Here is my point. Have you actually had a legit BMW tech who knows and understands what commands the compressor on? It could be a stupid sensor is broke or starts to work after it gets hot enough (from engine heat). I sure don't want to see you mess something up.

I get your comparison to diagnosis of diarrhea but the risk/reward scenario is different. You take Pepto in that case and stay home vs do God knows what to your AC system at high pressures, etc.

I get it that YOU WANT AND NEED TO BE COOL! I'm west of you and damn hot here too. We hit 102F yesterday.

Was this crap going on way back when you were still in 4 yr/50,000 warranty? Sorry, I have read your whole thread but not going back to reread for when this started.

Good luck brotha, we know you want to be cold.

[Asonchadwick]

I'm going with the battery also my car sat for a long time and the battery died. I jumped it and everything ran except the ac. Main cooking fan and vent fan not blowing just a little bit only.

[Tomnavigator]

BB_Cuda No I have not had a BMW tech look at it. I am over 50 miles from the nearest dealer and there are not very many BMWs in southwest Louisiana so I am assuming there are almost no BMW techs here. I also have not had a car worked on other than in warranty since I was 15 years old and don't really know how to find someone close. I also have a dumb ass pride that I do ALL my own work. I thank you for the complement that I seem to be a pro. I am not. I do however, get by. I know you live south of Houston. I think Houston is every bit as hot at SW Louisiana and worse in the city where there is no air flow and concrete all around. I do not know for sure but I kind of think my problem first occurred after I got my coding modification to my DDE. But, I have no way to confirm.
I think I finally figured out the wiring to the a/c compressor. It should have three wires. One 12 volt modulated control wire, one feedback wire, and one ground wire. I am going to do what you suggested (with a little twist) and splice three wires into the three wires. I will then monitor these wires with a fluke multimeter to determine which is the control wire and which is the feedback wire. When my parts come in I will modulate the control wire and the a/c should work and my problem goes away. Or I kill my a/c and learn another lesson of things not to do. Maybe by the time I am 90 I will have things figured out.

[Tomnavigator]

Asonchadwick - For many months last year I thought the issue may be the battery. I read that BMW programs the DDE to turn off the a/c if the battery voltage is too low. It seemed logical that the battery voltage from the battery may be the culprit and the car would have to run for 3 to 5 minutes to charge the battery to some magical voltage before the computer would allow the a/c to come on. I now always keep my BMW on a trickle charger. As soon as I get out of the car, I connect the battery to the trickle charger and disconnect it just before starting it to use the BMW. I tried reregistering my battery, cleaned the battery terminals and connections. Nothing worked and I decided it probably was not the battery. But, I was not willing to go out and buy a battery to totally rule out the battery. I keep my cars (I have 7), both motorcycles, both tractors, and zero turn mower on trickle chargers all the time. My batteries typically last me from 8 to 10 years. I have now definitively ruled out my BMW battery. My tractor needed a new battery a couple of weeks ago. Instead of buying a battery for my tractor, I bought a new battery for my BMW. I put the brand new battery in my 335D and installed the old BMW battery in the tractor. I registered the new battery in the BMW and charged the battery for two days on the trickle charger to make sure it was fully charged before I drove the BMW. Nothing has changed. I Still have no a/c for the first 3 to 5 minutes. I have now ruled out the battery and think the issue is some programming in the DDE.

[Tomnavigator]

Everyone I think BB_cuda helped me solve my problem. He asked me when this started. I looked back and my a/c issue started right after I had my car down for months working on it. I had ABS module issues, did emissions repairs, brake work, water pump, thermostat, and carbon cleaning. I caused my problems with the work I did and know what I need to do to fix it. I am on the right track with my pulse width modulator. When i get it installed in about a month or so, I will update everyone with the results.

[604x5]

So your Band-Aiding an issue you created with a pwm? Why don't you just fix it properly?

[BB_cuda]

Tomnavigator, PM sent

[Tomnavigator]

604x5 - You are right after ten months of trying to fix my car right. I give up trying to "Fix it right" and am willing to reengineer my car to make the a/c work. This is what you are calling "Band-Aiding" the a/c. I don't care what it is called if my a/c works. At some point I think it is smarter to reengineer the workings of the a/c and have a cool car than be stubbornly continuing to find the real cause and be miserable for another year with no results.
Last August, I admitted this problem was beyond me when I posted on this forum asking for help. I did everything suggested by others and I still have the problem and am still miserable in the summer. I now officially admit to the world that the problem has eluded me and is beyond my ability to diagnose the cause with a couple of self imposed limitations to investigating one possible cause to the problem. It however is not beyond my ability to fix. My reengineer/band-aid fix will not hurt anything and if it works, I will have a/c just like I should have. How many of the readers on this forum would come up with a reengineer/band-aid fix like this. I have other reasons I discussed with BB_cuda on the side as to why I am giving up on fixing it right as you infer. I admit The correct fix is beyond me but a workable reengineer of the operation of the a/c is not above my abilities.
I will post and let everyone know if my reengineer (band-aid) works. Keep in mind that if my fix works, I will only have $25 invested in fixing my car a/c. That ain't bad as they say.

[604x5]

Originally Posted by Tomnavigator

604x5 - You are right after ten months of trying to fix my car right. I give up trying to "Fix it right" and am willing to reengineer my car to make the a/c work. This is what you are calling "Band-Aiding" the a/c. I don't care what it is called if my a/c works. At some point I think it is smarter to reengineer the workings of the a/c and have a cool car than be stubbornly continuing to find the real cause and be miserable for another year with no results.
Last August, I admitted this problem was beyond me when I posted on this forum asking for help. I did everything suggested by others and I still have the problem and am still miserable in the summer. I now officially admit to the world that the problem has eluded me and is beyond my ability to diagnose the cause with a couple of self imposed limitations to investigating one possible cause to the problem. It however is not beyond my ability to fix. My reengineer/band-aid fix will not hurt anything and if it works, I will have a/c just like I should have. How many of the readers on this forum would come up with a reengineer/band-aid fix like this. I have other reasons I discussed with BB_cuda on the side as to why I am giving up on fixing it right as you infer. I admit The correct fix is beyond me but a workable reengineer of the operation of the a/c is not above my abilities.
I will post and let everyone know if my reengineer (band-aid) works. Keep in mind that if my fix works, I will only have $25 invested in fixing my car a/c. That ain't bad as they say.

Forgive me for sounding critical but I dislike repairs that are just a work around for a problem rather than fixing the root cause problem. It's ultimately you're vehicle and you can fix it however you like but a couple hours with ISTA or Protool performing some solid diagnostics might save you further headache.

[lnxguy]

Has ISTA ever been used to help diagnose your issue? Extremely valuable tool...

[Tomnavigator]

To All - I am almost 100% sure the issue is in my DDE programming and I don't want to reload the DDE. I also hate back woods work around fixes and have always been a believer of fix it right and fix it now. However, once I talked to BB-Cuda, I have come to the conclusion that the issue was in my DDE software. Therefore, the three choices are:
1) Live with the problem; 2) Reload the DDE software; or 3) Reengineer the a/c to eliminate the problem aka band-aid fix.

604x5 - I am sorry that I got offended by your post. I am sensitive because I take a lot of pride in fixing my cars right. So many people live with check engine lights and I can't stand them. The 3 cars I drive the most have a combined age of 52 years and none of them have anything wrong with them except the BMW. The only issue with the BMW is the a/c problem that has driven me crazy for a year. I really think the pulse width modulator reengineer of the a/c the best way to fix the issue.
I got my parts in and now have to decide whether it is worse to work on the car in the south Louisiana heat for a couple of hours to fix it or whether it is worse to put up with a hot car for 5 minutes multiple of times this summer and fix the problem this fall.

[Tomnavigator]

All - DON'T READ THIS IF YOU CAN'T STAND LONG POSTS OR CONTROVERCIAL ISSUES! I am going to explain why I think my a/c issue is in the DDE coding and why fixing the problem with a pulse width modulator is a proper fix. Just before I started having my a/c problems, I had my car apart for over 3 months doing everything I could to make my care more dependable. I replaced and reprogrammed by ABS module. I did a complete brake job. I replaced the transmission fluid and installed an aluminum transmission pan. I replaced the water pump. I replaced the thermostat. I replaced the belts and idler pulleys. I replaced some but not all hoses. I replaced the MAF sensor. I reloaded the DDE programming. I performed a thorough carbon cleaning. I did exhaust system work. I did extensive DEF system work.
A couple of months after I completed all my work (after the weather got hot) I noticed that the a/c was not coming on for about 5 minutes after the car was started. This only occurred the first time I started the car after sitting over night. The second time and there after each day when the car was started, the a/c started right up and worked fine. When the a/c was working it worked just like it should and blew cold air. In Louisiana in the summer your car can get to over 130 degrees and with 100 percent humidity opening the windows does not help much to cool down your car. I checked all the usual a/c issues and could not fix the problem. I posted on the forum asking for help. I did all the things suggested by fellow forum members. Still no fix.
I used a stop watch to see if the timing for the a/c issue was constant. It was close but not the same time each time. I monitored the coolant temperature and it appeared the a/c would come on when the coolant temperature got above 55 degrees celsius. This made me suspicious that the issue was caused by some computer logic since the issue occurred as the car warmed up and only occurred the very first time the car was driven after the car sat overnight.
I ruled out loose connections and wires because they typically don't connect themselves as you drive. Yes, I admit vibration can cause them to intermittantly connect. However, they are not going to always be disconnected after sitting overnight and then connect after a few minutes of driving and stay connected the rest of the day.
I ruled out bad sensors. Most sensors fall into two categories. Analog sensors like oxygen sensors, NOx sensors, MAF sensor, or throttle position sensor that have a variable output. These sensors usually fail gradually and/or by putting put out a weaker signal instead of failing completely all at once. The second type of sensor is a digital (on/off) sensor like a pressure switch, abs sensor, or camshaft position sensor. These sensors usually work or don't work. Neither analog or digital sensors fail by not working for the first five minutes then work fine from then on. However, some analog sensors like an oxygen sensor may be weak and have to get hot before working correctly. The oxygen sensor does not have anything to do with preventing the a/c from coming on to my knowledge.
I have also heard that BMW turns off the a/c any time you accelerate quicker than a certain amount to increase the acceleration and also turn off the a/c any time the battery voltage is below a certain voltage to allow the alternator to charge the battery first.
I just about decided the a/c issue I was having was caused by some weird DDE programming issue when BB_Cuda asked me a question that hit home.
BB_Cuda asked me the question what did you do to the car before the a/c problem started. This made me realize the one issue I had overlooked. I reloaded the DDE programming. This makes sense now. The issue is not sensors. I have the same sensors as before my work, It is not loose wiring or loose connections. Loose connections do not occur fir the first five minutes only. The issue is the DDE programming. The time and effort to reprogram the DDE is not worth the time, effort, and expense for to me. I will reengineer the operation of the a/c. Yes this is not the proper factory designed fix but a workable fix. It is no different than the people who get tired of the emissions related problems they experience with their cars so they install emissions delete tunes to eliminate the emissions equipment. Or the people who add performance tunes to obtain more horse power. These are not factory designed but reengineering of the car to solve a problem because fixing the problem "right" has been determined to be too difficult, not worth the time, and/or not dependable enough. This is why I will fix my a/c issue by reengineering the a/c.

A separate issue is some of the things BMW and other manufacturers do in the name of emission control or fuel mileage.

BMW does some things in the name of fuel mileage or emissions reduction that are not in the best interest of the owners of the cars and I do not agree with. BMW programs some cars to not charge the battery unless the car is coasting. In the USA many drivers never coast. I have a friend that had a BMW 545i. He is a non coaster that drives with his foot on the accelerator or the brake. He coasts for about 0.1 seconds which is the length of time it takes him to put on the brakes after he takes his foot off the accelerator. He always brakes hard which means the time for charging the battery is minimal. Because of his driving style, he replaces the battery in his car every 18 months because his batteries always go dead.
Another BMW programming issue related to fuel mileage is having to register/program the DDE every time you replace the battery. We all lovingly call this registering the battery. Registering the battery is required because the car charges the battery at the lowest minimum level needed to keep the battery charged in the name of fuel mileage. Look at what it cost the average BMW owner to go to a dealership to register the battery every time a battery is changed and all because BMW wanted credit for another 0.1 MPG fuel mileage with the EPA. No other car manufacturer in the world requires a car to be reprogrammed just because you change the battery to one that is higher or lower output or change from a conventional to AGM battery. All BMW owners should be pissed off that BMW does not give a S**t about what BMW is costing their owners unnecessarily for things like requiring battery registration. Who likes throwing away $100 to $300 every time a battery is replaced to have a dealership register the new battery? My 2003 corvette needs a new battery about once every 7 years and costs $300 to replace at a dealership. My BMW needs a new battery about once every 6 years and costs $500 to $600 to replace at the BMW dealer. This is almost twice as expensive as it costs to replace my corvette battery. Does anyone really believe registering the battery of a BMW makes the battery last last twice as long? We do know that registering a battery can double the costs of replacing a battery at some dealers.
I worked 18 years for General Motors with the last 8 years as an engineer at the corvette assembly plant in Bowling Green, KY. I know the efforts car manufactures are willing to go to in the name of emissions controls and fuel mileage. General Motors shipped the corvettes to the dealers with about one gallon of fuel in the tanks and with the windshield washer bottle empty. This was done to reduce the as shipped weight of the corvettes. The EPA fuel mileage of a vehicle is test is done on a dynamometer. The resistance of dynamometer is set using the as shipped weight of the vehicle. The weights of the vehicles fall into weight classes such as 2800 pounds to 3200 pounds. All the vehicles in this weight class are tested using one dynamometer setting. Vehicles from 3201 pounds to 3500 pounds fall into another weight class and use another dynamometer setting. General Motors could get the as shipped weight of the corvette into a lower weight class by shipping the cars without windshield washer fluid and with an almost empty fuel tank. General Motors would then pay the dealership to fill up the fuel tank and windshield washer fluid tank before delivering the car to the customer. General Motors did this even though dealerships charged about 50% more for the fuel and about $30 to add a gallon of windshield washer fluid to the car. All in the name of fuel mileage. At least this was transparent to the customer and the customer never know it was going on.
Other programming thing that BMW does are things like, programming the DDE to turn off the a/c any time you accelerate quicker than a certain amount to increase the acceleration and also turn off the a/c any time the battery voltage is below a certain voltage to allow the alternator to charge the battery to a predetermined level before allowing the a/c to come on.