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Tuesday, April 23, 2024

Doug's Domain

Doug Vetter, ATP/CFI

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Tuesday, April 3, 2012

Chuck Engine Light Reveals Cam Sensor Faults

Last night, shortly after I started the car to head home from the office, I realized that the CEL (otherwise known as the CHUCK ENGINE LIGHT) was illuminated. Rats. The vehicle seemed to run nicely all the way home so I assumed it wasn't anything critical. Still, I couldn't help but give my personal diagnostic subroutine a crack at the task. By the time I reached home I didn't have any viable theories so I decided at that point to simply get up early and take the car to my technician for access to his eons of experience and, of course, the BMW diagnostic computer.

After a brief search at the dealer this morning I found my technician hiding in the rear shop -- which I found to be refreshingly quiet as compared to the front shop -- and I only had to wait a few moments for him to finish up a phone call to solicit his assistance. While I waited I noticed an E92 coupe up on the lift with both tires on the left side of the car sporting a sizeable bubble in the sidewall. Someone had obviously hit a pothole and taken out at least $400 worth of tires (well, at dealer cost more like $600) and perhaps a couple wheels at $600 a pop. This can happen to anyone, especially as the roads deteriorate due to misappropriated budgets, but from what my technician says he sees many repeat offenders. That could be due to environment (some towns in NJ spend as little as 10% of their tax revenues on road maintenance, which I find reprehensible) or a lack of driving skill but it's probably a little of both.

When it came time to grab the diagnostic computer and probe the depths of my E36's DME for trouble codes my technician instinctually reached for the old GT1 because apparently the newer SSS still has trouble talking to the older cars, particularly with respect to its ability to reliably clear codes. "The problem", my technician recounted, "is that after you fix the problem by replacing whatever components were required, it fails to clear the codes and tricks you into thinking the problem still exists and that you have to continue troubleshooting". So new is not necessarily better. Gazing at the battle-worn wireless diagnostic head connected to my 20 pin connector I commented "man, you don't know how much I want one of those". He smirked and replied "yea, you and all the other dealers."

A couple minutes later the GT1 had successfully communicated the source of my CEL -- two cam position sensor faults, the last of which occurred about 2 hours ago (drive time). That didn't make much sense to me as I hadn't driven the car more than about 45 minutes since the CEL first appeared, but I wasn't about to question the diagnosis. My technician quickly showed me the location of the sensor I needed to replace. That rang a bell and I realized simultaneously as my technician explained the corrective action that I'd have to pull the airbox, alternator duct, vanos solenoid, and perhaps the CCV and vanos oil supply hoses out of the way to gain access to both the sensor and its electrical connector located under the intake manifold. After the GT1 predictably and quickly cleared the codes I drove over to the parts department to pick up a new sensor. I assumed that they would have to order the part but was surprised to learn that they had the part in stock so I picked it up today at a much appreciated 35% discount.

At this point I figured that I'd drive the car until I could afford the time to replace the sensor since it continued to run well. Of course, you know what they say about the best laid plans. This evening I channeled Phil Connors when I started the car to go home only to see the CHUCK ENGINE light appear again. Double rats! This time I got out to listen to the engine and exhaust only to hear a very slightly unstable idle. Since I know camshaft sensor faults can cause the engine to run rough or fail to start at all, I took this as a sign that I should bring the car to the garage and swap it for the E46, if for no other reason than to avoid the hassle and expense of a tow should the sensor decide to give up the ghost permanently.

I showed up at the garage some 30 minutes later and found my baby waiting patiently for me after months of slumber. I turned the key and she eagerly fired on the first cylinder. A quick check of the tire pressure using my recently purchased gauge revealed the need to fire up the compressor, but I made quick work of that, transferred my stuff into my new(er) chariot, and headed home. I expect to replace the sensor later this week.

Mileage: 220160, Labor Saved: $80, Parts: $105, Parts Saved: $70