Monday 19 September 2011

E39 530d: Replacing the Camshaft Position Sensor [M57]

About four months after I bought the car it suddenly refused to start after having been turned off for about 20 minutes, even thought it had started fine on the short trip out. The starter motor was turning but the engine wouldn't fire. It started after about 30 minutes so I assumed it was because the car was low on fuel and the problem didn't return for a number of weeks.

When it eventually became regular I noticed that it only seemed to be when the car was left to cool for a while. The car would start fine from cold every morning or soon after being turned off, but left to cool for half an hour and the engine was dead for, at the very least, 4 or 5 hours.

Asking around on forums brought up several possible culprits - a fuel-pump, most likely the pressure-pump under the passenger seat, low fuel-pressure caused by, at the worst, a cracked injector (gulp), or an engine-position sensor on the camshaft or crank.

After a while we took a guess at it being a sensor, as the car would sometimes start after being rolled a little while in gear, which seemed to rearrange the engine and get the sensor going again. Thankfully I eventually got some diagnostics, which confirmed it was indeed the camshaft-sensor.

It was tricky to diagnose, but if you have the same symptoms then this is the first thing to look at. The replacement sensor I got from eBay wasn't too cheap either at £60, but its a brand new part and guaranteed.

Removing and refitting the sensor couldn't be easier:

1. Remove the beige centre-section of the engine cover by first undoing the single bolt to the rear with an M4 allen-key and then pulling it up towards the front until it comes away from the stud at the front.

2. Unplug the camshaft-sensor by pressing the latch of the clip inwards and sliding the wire-connector off the sensor.

3. Remove the single screw securing the sensor in place using a T10 torx-head wrench.

4. Gently twist and pull the sensor clear of its base on the cylinder-head.

5. Insert the new sensor into the cylinder-head, remembering to replace the old rubber O-ring if it doesn't have a new one fitted, and make sure it is well seated before replacing the torx-head screw.

6. Reverse steps 2 and 1.

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