2001 BMW 525i 90,000 miles, starts, runs perfect, sets P0340 DTC


Hi folks, looking again for a possible cause of an automotive problem, or more specifically, the cause for the computer setting the P0340 DTC, as the car starts and runs fine. The stated reasons in a google search for the code being set vary from bad sensors, bad wiring, bad PCM, bad alternator, stretched timing belt, damaged or dirty reluctor ring, weak battery etc. etc.

The most crucial information is that there are absolutely no driveability problems with this car. It belongs to my neighbor. His wife just bought it a few weeks ago from a relative after she wrecked her car. He drives it and she drives his 1998 Jeep GC, which is known to be reliable. He says the car scares him because it has so much power.

Another piece of relevant info is that after getting the codes cleared, it took over a week of daily about town driving for the code to get set again.

I should also mention that the computer also sets the P0128 DTC, which seems unrelated to me. Any clues as to this behavior, setting the P0340 DTC, but no driveability problems?


it is quite clearly points that engine computer does not like camshaft sensor signal, either because sensor is bad or wires to sensor are bad or due to other factors like bad timing or overall power quality issues

since code is not popping up immediately after reset, I would suspect timing or power problems (like old battery, corroded ground connections or such)

for the timing… what’s vehicle mileage? how regular were oil changes? was only BMW specked oil used?

if mileage is high or oil was not regularly changed or oil was not adhering to strict BMW requirements, the timing chain may be stretched and it may result in bad timing

Thanks, gd, these are things I can check before throwing parts at it.

Mileage is 90,000, car looks almost new. Can’t say what oil was used in oil changes. Previous owner may have that info. I can pass it on to the current owner.

Doesn’t matter what was used in the past . The manual will say what oil and other fluids to use . Any name brand of the correct weight will be fine .

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Curent owner assures that correct oil was used. Engine is M54, which has a timing chain, and one individual on another site says that BMW timing chains never need maintenance or replacement and are good for the life of the engine, which, again, is 90,000 miles. And as there is noway to adjust the timing, and car runs like an unchained beast, I think we can rule out timing as the problem.

BMW cam position sensors do sometimes fail. I have replaced one and read posts of several failures through the years. Advice in this thread is all good. I think that is a shielded wire so check the length of the wire for pinching or chaffing. If the connection is clean, and the engine cranks briskly, try a new intake cam sensor. Easy to replace.

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That is generally true IF the oil has been changed as it should be. Based on the age of the car and the relatively low odometer mileage, it has been driven–on average–less than 5k miles per year. That usually indicates that the car was used solely for short-trip, local driving which is considered to be “Severe Service”. That means the oil should have been changed twice per year, despite not having been driven many miles.

Unless you can confirm that the oil was changed twice each year, then it is entirely possible that lubrication issues have led to damage to the timing chain.


+1 to @VDCdriver advise

low mileage may be indicative of disproportionately high number of short drive cycles, which actually bring more wear&tear than longer drives, also some people seem not to be able wrap their heads around definion of “replace oil at X miles or Z months, whatever comes first”, which can contribute a lot to wear of old low-mileage engine

another concern here is: was the “proper” oil used or car was maintained at some “quicky lube” place?
the trouble is that BMW oil spec is substantially more demanding than the “typical” oil used here in USA, and using wrong oil type can absolutely shorten the life of the engine and timing chain substantially

I would agree to the advise given above about checking wiring and replacing cam sensor, although it might be what is called “throwing parts on the issue”

If engine provides the inspection port on the front cover to inspect how far chain was stretched, I would consider opening it and inspecting the actual chain wear to be sure

Got word last night from the current owner that the previous owner, his grandson, replaced both the intake and exhaust CMP sensors in an effort to deal with P0340, although not sure what brand. Will take a close look at wiring at next opportunity.

I have never heard of a cam chain wearing out on a 6 cyl BMW engine. My daily driver 2004 has 250k miles on it and I recently sold a 1997 with 335k miles on it. Cam chain guides can get old and brittle and break, but I don’t think that is the problem here. Another thing that can happen on an 19 year old BMW is that the VANOS O-rings get old and hard and leaky. I can imagine leaking O-rings possibly causing a P0340 code, but if that were happening, I doubt that the OP would be reporting that the car is quick. A 525i is not a particularly quick car by BMW standards, even under ideal conditions.

Thanks, current owner’s grandson changed both in an effort to deal with P0340 DTC. Trying to find out what brand. Came across a great thread that highlights the advantage of OE parts. Tracked down a good price from a reputable seller. If it turns out the new ones are cheapies and everything else checks out, that may be the problem.

People can drive BMW vehicles in all kind of ways which makes me wonder about his driving skills.

I was thinking the same thing, as greendragon suggested timing could be the problem. I am from the old school and immediately thought, “Well I can check that with a timing light.” Then I woke up and remember we are well into the 21st century, and started googling. That’s when I learned about the VANOS, which dynamically adjusts cam timing. I realized that must be what greendragon was referring to, not ignition timing. So the VANOS is also on the suspect list. Does that sound reasonable?