Over the past seven months or so, I’ve had an intermittent issue with my E39 where it randomly stalls at slow speed. Thankfully the issue only happened a few times spread out over several months. The difficult part about this issue was that the service engine light never came on and provided codes as a starting point for diagnosis of the issue. I suspected that either the camshaft position sensors were starting to fail, or that the MAF was starting to fail. Both were very plausible considering the symptoms and original mileage on those parts, which is 135,000 miles.
Last week I was driving through a shopping center parking lot, and the car stalled. I cranked the key to start but it just cranked for a long time without starting. Finally, by pressing the gas pedal while cranking, the car came back to life and I limped the car a few miles home. The service engine light finally came on at this time, providing me with the diagnosis code P0340 for the camshaft position sensor malfunction. I knew right away that the sensors needed to be changed.
After ordering a new intake camshaft position sensor and installing, the car was 100% again. It definitely had restored power and more throttle response, which was previously degraded due to the failing electronic sensor. I also ordered the exhaust cam position sensor, which I will replace this weekend as a preventative measure. These two wear items are likely to effect fuel consumption as well, so hopefully gas mileage will improve slightly with the new sensors.
Below is the video just uploaded to my YouTube channel detailing the diagnosis and replacement of the intake camshaft position sensor. You can order a new sensor here.