- Somewhere in here is the crank sensor

My Alfa Life: Too Hot To Handle

27w ago


The Spider has been running pretty well, albeit not being used that much due to me having snapped my Achilles' Tendon. Yes, I've still got to fix the clamshell motor, other than that its been a nice reliable 17 year old car. That was until she developed a case of the teenage sulks.

The first of these was at the Burton Waters Classic Car meet. She was fine driving down, driving across the uneven ground to park up, and being admired. What she didn't like was starting when it came time to leave. In the end we called the AA, and left her whilst we grabbed something to eat and drink.


When we came back to the car, before the AA had arrived, it appeared the abandonment and silent treatment had worked. She fired into life straight-away and we were able to get home no problem.

Again, all seemed fine, until the temperature decided that it would be more Southern France than Northern England. At one point she wouldn't start whilst sat in the driveway. After being left with the bonnet open for a little while, sense prevailed and she started. At this point I should have done some research on the matter but foolishly didn't.

We went out for lunch and, with the weather being hot and sunny, took the Spider prior to using her for the trip down to the National Alfa Day on Sunday. After a great lunch outside in the baking sun we got back to this.

Again the bonnet was popped, wires were wiggled, and with no luck the AA was called.

In the meantime I consulted the Alfa Romeo 916 Owners Club via Facebook with details of the problem on the off chance that someone would come up with something. The two things that came back were; ignition circuit, and crank sensor.

Alfa Romeo 916 ignition circuit connections

The ignition circuit was easy to check, pop the fusebox cover and unplug/replug a set of wires. Sadly this made no difference. The crank sensor would be a bit tricky without a diagnostic unit. Fortunately the AA arrived, two very nice men, and they had one of these. Here is the output:

Engine control 1 - 29F / Motronic M 1.5.5. P0335 - Speed sensor.. Error Message : No signal.. P1653 - Camshaft control. Error Message : Open circuit

The first fault is the crank sensor. Without knowing the position of the crank the ECU can't determine when to spark so doesn't. In typical manner though, when the AA man turned the key the engine fired into life.

The explanation was that the sensor is driven by a magnet. This is reinforced with a copper winding. As the part heats the copper expands and this has an effect on the sensor's ability to generate a signal. Its fine once its running but once you stop it won't work again until it has cooled enough for the copper to contract.

Once home I called around the local Alfa Romeo dealers but no one had one in stock so I ordered one online. This arrived a few days later and, after trying to fit it myself but not really being able to find it, took it to a local specialist who fitted it free of charge. This fixed the problem and starting has been fine every since.

Somehow though the clamshell release motor has now decided not to play anymore so I'm back to using the special tool provided in the tool kit to release and lock it. The hood partly goes up using the button but taking it down is a manual job for the moment. All part of the joys of Alfa Romeo ownership.