The 'check engine' light is on


Gentlemen, I drive a manual 1997 BMW 318i which has 150,000 miles on its odometer. Lately and not every day, the ‘check engine’ light on the dashboard lights up. It’s a steady light, and it does not flicker. The car runs and operates smoothly. Mostly it occurs on wet and rainly days. Has humidity something to do with it?

How concerned should I be, and am I endangering the motor?

I would greatly appreciate your advice, and I thank you in advance.

Horst Steinfels

Nobody can tell you what the severity of the issue might be until you have the stored trouble codes read.

Auto Zone, Advance Auto, O’Reilly (and possibly Napa) are places that can scan the car’s OBD system for stored code(s)–without charge. Then, come back here to post the codes for specific help.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Gentlemen, I thank you for your quick reply, and following your suggestion I had my car checked. The test result read P 0340.

I greatly appreciate your specific help.

Horst Steinfels

P0403 generic code, EGR circuit malfunction. Could be a simple vacuum hose,or carbon build up, or a wiring issue, or a part failure. Let me see what the only manual I have says, perhaps something gets knocked loose in my brain.

Got that totally wrong it’s P0340 also generic code,camshaft position sensor circuit malfunction, if it’s hooked up almost certainly a part failure.

Try some 'googling" perhaps more accurate info about posibilites can be found. Not suprised you don’t notice any performance issues.

If it is P0340 (as opposed to P0403 as oldschool read - I reverse numbers a lot too) then this refers to a problem in the camshaft position sensor (CPS) circuit. It is somewhat odd that you would experience no symptoms, but if you ignore it for long you likely will.

You can read a little bit about it here:

The short story is that one of the engine’s critical sensors probably has a worn and/or loose connector, or some damage somewhere along it wiring route. I call it “critical” because the signal for this sensor is needed for correct timing of the spark (no spark, no boom, no go). The damp weather is the first warning as the dampness messes with the electrical signal.

The most straightforward first step is to pull the connector for the sensor, inspect it, clean it, give it a shot of dialectric grease and plug it back in.