2001 E39 530i CEL Mystery - Repost from broken thread

[AntrhaciteE39]

Off to a rocky start here... try and create a thread and the post disappears and I cannot delete it! Onto my original problem statement...

I have had a very persistent CEL that does not seem to disappear. I have replaced a good number of parts and both myself and the shop I go to are baffled. They are a shop with a good reputation, specializing in BMWs with a constant flow of customers. Most of the parts below have been provided gratis since the problem does not go away, so they aren't making money on this.

The car itself is drivable, no misfires, smoke, or anything really weird. Why am I investigating this then? Gas mileage and hoping to avoid expensive a rippling mechanical issues if possible.

New parts: pre-cat O2, oil separator (was perforated) & vacuum hoses, MAF, engine coolant temp. sens. switch, alternator (probably unrelated but was replaced recently), 4 coil packs have been replaced (2 recent, 2 two years ago),I am on the latest version of the software (updated 2 years ago, nothing custom)

Codes: P1093, P1092, sometimes P0117 (tested for repeatability 4+ times, 1093 and 1092 most persistent), all 3 listed "not current" when tested at mechanic.

The only thing I can think of is maybe a bad software load has had my vehicle constantly confused. Is this a possibility? The car sees regular preventative maintenance (oil change etc) and is not modified in any way. (I have an ipod hookup attached to the CD changer wiring harness in the trunk that's it!). Mileage is ~120k.

I hope you guys may be able to shed some light onto this problem. Let me know if there's any more information I can provide.

Thanks.

[MarcoZandrini]

"P0117" equates to " Engine Coolant Temperature Circuit Low Input." This could indicate that the temp sensor is intermittently faulty. The other two codes indicate that bank 2 (cylinders 4, 5 and 6) are running either lean (P1092) or rich (P1093). The pre-cat oxygen sensor for these cylinders determines the oxygen levels. Btw, there are a total of 4 oxygen sensors: each bank has a pre-cat sensor and a post-cat sensor. The post-cat sensors are used to determine the effectiveness of the cat.

These codes (P1092/3) could be related to the P0117 issue in that if the temp sensor is flaky the ECU may be compensating by adjusting the mixture. Why no similar bank 1 errors? Sometimes an oxygen sensor is more sensitive than its counterpart. Your post notes that an oxygen sensor has been replaced. Do you know which one?

[AntrhaciteE39]

Marco thanks for your reply!

The pre-cat O2 for bank 2, sorry for not clarifying. Also the CEL turned itself off for my morning commute and back on again during my return. Not sure if this is trivial or another symptom.

[dworthy]

There are 3 engine temp switches one in the radiator, and two in the head area. Do you know which one for sure was replaced? It should have been this one: http://www.realoem.com/bmw/showparts...69&hg=11&fg=15 #3 on the head.

[AntrhaciteE39]

The switch that was replaced is #3 in the diagram you provided, clarified with the mechanic today.

[dworthy]

Next you will want to do a smoke test to find where the vacuum leak is, with any lean condition/codes you have unmetered air entering the motor.

[AntrhaciteE39]

A smoke test was performed, which is why they replaced some vacuum hoses and the perforated oil separator. What they are claiming now is that an oil leak found its way to a crank case sensor and is screwing it up. No word on if that has fixed anything but that's where we're at now... If nothing else at the end of this maybe the community will learn of some really strange way that these codes can be triggered!

[dworthy]

Even though they did fix what they found, was another smoke test done after the replaced all the broken/bad parts?

[White94RX]

Why don't you take it to someone who knows what they're doing? Lean codes are really easy to diagnose when you know what you're doing. Like a dealership with actual BMW Master tech's.

[AntrhaciteE39]

The answer right now appears to have been that oil wicked into the DME via the wiring. They cleaned it all up and I've been good for 70+ miles.