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Old 01-05-2016, 03:33 PM
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Quote:
Originally Posted by jdstrickland View Post
If you have P0301 thru P0306, then P0300 just says that you have the others. P0300 is MULTIPLE RANDOM MISFIRE, whereas the individual misfires are reported separately.

If the Check Engine (SERVICE ENGINE SOON) light is not on, then I'd suggest that you do not want to reset the codes. Codes come in two forms, active and pending. Until the check engine light comes on, the codes stored are pending. This means that an event happened once and the computer is waiting to see if it happens again, at which point it will become active and trip the light.

The 3.0L engine in your X is the same M54 that is used in the 3 and 5 Series cars. It's a little bit different than the earlier, M52, but there are similarities that might be well to keep in mind.

I bought a 323 that was giving P0300 codes, and every once in a while a MAF code would come up. I also had a few instances of P1188 and P1189, which are BMW codes for deviations in the air/fuel ratios -- basically the mixture swings from rich to lean and back again. The problem ended up being the MAF.

What the MAF does when it is working is measure the air density so that the fuel delivery can be such that the ratio is 14.7:1. This ratio is not so important to the engine, but the CAT likes it a lot. Turns out that the chemical reactions that take place inside of the CAT allow an even distribution of molecules when the ratio is 14.7:1. Bottom line is that the CAT wants a steady A/F ratio. The engine cares somewhat, but has a much wider range of acceptable mixtures, so the CAT is what is driving the bus here.

In any case, the MAF can fail in such a way that while the air density is a constant, the reports to the computer is that the air density is changing, the result being that the fuel delivery also changes and this causes the mixture to swing from lean to rich and back again. If the air density really is a constant, but the MAF is reporting it variously as dense or thin, the fuel ratios would be changed as the reported air quality changes.

I'm not suggesting you rush out and buy a MAF, I am only suggesting that you keep it in the back of your mind that it might be the root of your problems. My issues were with the M52, and the M54 can easily be different. But the M54 could be the same, I simply do not know.

I struggled with my car at home for a weekend, and then drove it across town to a BMW guy that I see once in a while. He hooked up his GT1 diagnostic, and said within about 3 minutes that a transistor gate was shorted to ground inside the block of epoxy that houses the circuits inside of the MAF. I was having similar problems as you, P03nn codes without any noticeable affect in drivability. I had the P1188 & P1189 codes, which are cousins of P0171 and P0174. Technically, they are the same as P0170 and P0173 FUEL CONTROL/TRIM MALFUNCTION. Fuel delivery faults can be reported as lean, rich, or malfunction. My logic says that rich and lean are consistent errors in one direction or the other, malfunction would be errors in both directions.

So, work through the cheap stuff first, but be prepared that somebody might tell you that you need a MAF. Due to the cost of a MAF, I'd go ahead and pay for a scan with the GT1 diagnostic package that most shops will not have because it is expensive. I'd call the local Independent BMW garage and ask if they have the GT1.
I think someone already mentioned that at the beginning of this thread.

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