Does ECU use a default tune when engine light is on?

[AlwaysOverkill]

I am sure this applies to every OBD 2 vehicle but since I have a BMW I might as well ask it here.

I have a 2009 328i and the check engine light has been on for several months now for a misfire cylinder 4, and I believe the misfire only happens on start up because it seems to rattle and run rough for a couple seconds when its cold but seems to run perfectly fine after that. Smooth, powerful, and predictable. As well as all features work fine, A/C, radio, trans shifts fine, ect. If you want to know more to the story as why it has been on for months then read below.

But for right now my question is this:

When the check engine light is on, even for a reason that does not result is any loss of performance/efficiency. Does the ECU revert back to a default tune or a limp mode of some kind? I know after you change the battery or reset the codes it has to do a “learning” cycle where it then optimizes performance. Is that process halted while the check engine light is on?

Just curious and because I am wanting to know what I can look forward to when the light is finally fixed.


Since I know people will be all over me for driving around with a light on, it is because the vehicle is still under SULEV warranty and every time I bring it in they throw more and more parts at it but have not been able to fix it yet. The problem is so intermittent that after they fix something they cant get the light to come back on. Its not until I drive it around for a couple days and it decides to fire up rough one day that the light finally pops on.

So far they have changed:
Spark plugs
Coils
Engine wiring harness
Vacuum lines
Eccentric valve sensor

I have been able to self diagnose the vehicle because the misfire was in cylinder 2 and then I swapped cylinder 2 and 4 fuel injector and sure enough it followed the fuel injector and misfire immediately went to cyl 4. I told the service rep that but he said that they still have to go through all their own procedures in order to diagnose it and somehow they haven't found it yet. He also said its best if we dont tell them that I have been messing with it. The reason I haven't changed it myself is because I can either change 1 injector myself and it will cost me $150. Or when they finally find the problem they change all 6 injectors and it will cost me $0. So I would rather have them do any warranty related repairs and I do my own maintenance related work like changing all the oils and stuff.

[MarcoZandrini]

The engine computer (DME in BMWspeak) has several modes or maps which it uses. The first is the cold start map. When the engine temperature, as determined by the coolant temperature sensor in the cylinder head (in most cases), is below a specific point the DME uses the cold start map. This runs an overly rich fuel/air mixture for up to about 90 seconds. This gets the catalytic converters up to temperature quickly. The DME also runs the secondary air pump (SAP) (if you car is so equipped) at the same time. The SAP dumps air into the exhaust manifolds to ensure the overly rich mixture fully burns. Then there’s the “normal” map which the DME uses 99% of the time. Now, in this mode the DME can a wide variety of things to balance performance, emissions and fuel mileage. Your engine has variable valve timing and maybe variable intake valve opening (Valvetronic). These are under the control of the DME. Lastly is limp mode. This occurs when the DME and/or the automatic transmission computer (EGS) detects a problem which could could damage the engine and/or the automatic transmission if the car is normally operated. In some cars the limp mode forces the transmission into 4 gear and reduces power. Now, cars with a turbocharged engine (like my M240i) have an additional map that’s used even if the engine is hot. That is, at start up the DME revs the engine up to about 1200 rpm for 15 seconds or so. This is to ensure that the turbo, which is lubed and cooled by engine oil, is getting the proper volume of oil at the proper pressure. The first thing I do when I get into my car is depress the clutch (he has a manual transmission) and start the engine. While the engine is revving at 1200 rpm I get ready to drive the car.

[AlwaysOverkill]

Some really good info there! Since I am sure my problem is a fuel injector and because it only does it when its cold there must be a problem with it dumping way to much fuel on start up due to it been stuck partially open possibly? Not sure just a guess but the fact there there is a different fuel map for start ups and that is my problem then im probably in the right area.

Secondly though, and what my original question was, does it use the “normal” map when the engine light is on and still use the wide variety of things to optimize performance, emissions, and fuel mileage, or does it stay within the default parameters of the map without adjusting itself due to a sensor or part of some kind possibly not being able to make proper adjustments that the computer is asking for?

[shogun]

When the engine light is on it will probably run in LOS if it is a serious fault , this is for M1.1 and M1.3, but the basic function is all the same

Limited Operating Strategy (LOS)
In the event of a serious fault in one or more of the sensors or their wiring circuits, Motronic will substitute a fixed default value in place of the defective sensor. This procedure is often termed limp home. A serious fault occurs when the signal from the sensor is outside of its normal operating parameters. When operating in LOS the engine may actually run quite well with failure of one or more minor sensors. Since the substituted values are those of a hot engine, cold starting and running during the warm-up period may be less than satisfactory. Also, failure of a major sensor, ie the AFS, will tend to make driving conditions less easy. Once the fault has cleared, Motronic will once more accept the live signal from the sensor. The following LOS measures are taken in the event of a failure

Component..............................Action
AFS........................substitute values are calculated from the TS position. The load signal is fixed to 6.0 ms and the ignition timing to 20° BTDC once the TS contact is open.

ATS........................substitute value of 50° C . A code will not be set, and LOS will not commence until a minimum of 3 minutes after engine start and the engine idling for a minimum of 30 seconds.

CID sensor.............injectors are pulsed simultaneously

CO pot..................substitute value of 2.77 volts

CTS...................substitute value of 80° C if ATS value is greater than 20° . if ATS value is less than 20° , substitute value of ATS value for first three minutes after engine start-up.

OS.....................substitute value, open loop control

TS.....................substitute values, restricted engine operation

https://www.bimmerforums.com/forum/s...ic-1-1-1-3-BMW

The easiest would be if you have a diagnostic tool and after you have repaired a part like a temperature sensor, reset the DME and clear all faults, drive and then test with the diagnostic tool if there are still faults. Otherwise you might still have faults shown which are already repaired.

[MarcoZandrini]

Thank you shogun!

[AlwaysOverkill]

Wow thank you thank you! But I am not sure what some of those acronyms mean? Lol

So it does appear to be true that with the engine light on its possible that it is some form of an open loop mood where at least one of the many parameters is given a default value to use. Really cool to know.

[shogun]

see the link for the abbreviations
Air Flow Sensor (AFS)
ATS air temperature sensor: The ATS is mounted in the AFS inlet tract and measures the air temperature before it enters the inlet manifold.
CO pot: The CO pot mixture adjuster is a three wire potentiometer that allows small changes to be made to the idle CO. A 5.0 volt reference voltage is applied to the sensor and connected to the AFS earth return circuit. The third wire is the CO pot signal.
As the CO pot adjustment screw is turned the change in resistance returns a voltage signal to the ECU that will result in a change in CO. The CO pot adjustment only affects idle CO. Datum position is usually 2.50 volts. On catalyst equipped models, the CO pot has no effect and the CO is thus non-adjustable.
CTS coolant temp sensor: The CTS is immersed in the coolant system and contains a variable resistance that operates on the NTC principle.
CID sensor = cylinder identification sensor

https://www.bmwsections.com/info/abbreviations.php

[ross1]

The DME(engine computer) will shut down(cut fuel) any cylinder that has misfires beyond a certain limit.
If your #4 misfire is the only fault, "they" have changed all those parts chasing this and you've discovered that the misfire follows the injector it seems there is no question to answer, other than who is "they" that couldn't find this?
Be aware that mechanical issues can also cause misfires and sometimes "techs" accustomed to leaning on diagnostic computers and exchanging parts others have paid for will miss these basic problems.
If indeed you've solved this then wouldn't you rather change an injector for new yourself than have someone who is clearly incompetent continue to put hands on your car?

[AlwaysOverkill]

Yeah well the whole thing is that the car is still under warranty, so as long as they are willing to throw parts at it then I will keep bringing it back. I have repeatedly told them that the injector is the problem but because it is so intermittent and only during fire up then it is hard to find for them. Like I said I can either spend $150 on one injector or I can wait for them to find the problem and they will replace all 6 of them for free. And in the meantime they will probably change more parts. Also they said if they keep working on it and cant fix it then they will replace the whole engine so right now its worth letting then handle it.

But finding and fixing the problem isn’t really my question anymore, really I was more interested in knowing what the computer does while the light is on.

[ross1]

Yeah well the whole thing is that the car is still under warranty, so as long as they are willing to throw parts at it then I will keep bringing it back. I have repeatedly told them that the injector is the problem but because it is so intermittent and only during fire up then it is hard to find for them. Like I said I can either spend $150 on one injector or I can wait for them to find the problem and they will replace all 6 of them for free. And in the meantime they will probably change more parts. Also they said if they keep working on it and cant fix it then they will replace the whole engine so right now its worth letting then handle it.

But finding and fixing the problem isn’t really my question anymore, really I was more interested in knowing what the computer does while the light is on.

Okee-dokee, your time spent, sir. They must have a very nice waiting room.

[Niheem]

Wow great stuff