Crankshaft sensor problem

My Astra H (engine code Z18XER) is running like a tractor. The only fault code I continually have is the ‘P0335 Crankshaft Sensor Open Circuit’. I’ve replaced the sensor and checked resistance and voltage, but all is fine.

This has been a project car after a piston disintegrated on cylinder No 4. The pistons had been replaced with plus-sized items, so I assume it had cylinderhead/ engine problems in the past. Before the piston exploded, if you kicked down on accelerator while driving, a huge white cloud of smoke came out the exhaust. Head gasket failure, maybe?

I’ve since replaced the bottom engine with standard pistons and replaced the cylinderhead twice, yet still have this one fault code. I’m convinced it’s down to the crankshaft pick-up ring, but this is a nightmare to access because it acts as the rear crankshaft seal, so it’s an engine-out job. How can one sensor create such problems?

Mark Anthony Summersett

The crankshaft sensor pick-up may well be the problem and is going to take a few hours to replace. I wouldn’t recommend using a budget part, but rather go for a genuine or branded item. One possibility – which is not possible to check without removing the gearbox – is that the sensor is not sitting perfectly flat on the back of the engine. I have heard of cases where the locating tag on the sensor ring is slightly too wide and does not allow the sensor to sit perfectly flat. The smallest deviation from the correct position will cause a problem. The torque setting for the sensor ring is 4.5Nm.

Having checked the resistance and voltage, the problem may not be with the sensor itself. It would also be worth confirming the continuity and resistance of the wiring between the sensor and the ECU, to ensure there is not a problem in this area. Having eliminated the wiring, I would then re-check the valve timing, as this could also give the symptoms you have, and as the cylinderhead has been removed it is possible that a slight error has been made when timing up.