Camshaft sensor issue

[MixerFistit]

Looks like my post was deleted with yesterday's maintenance so I'll reconstruct.

Buried deep in the bowels of Lexia/Injection I have the following error:

Temporary Fault
Crankshaft - Camshaft synchronisation - No Camshaft sensor signal

(P0340)

I've cleared and it returns next journey. I don't seem to be having any problems with starting/driving and everything sounds fine. I'm not sure how long the error has been there for, it doesn't show up on a standard OBD II and doesn't even show up on the Scantool facility with Lexia.

Recent work - have taken timing belt off to repair fuel pump and everything seemed to go back OK. I did also unplug the camshaft sensor to move the whole harness away from the fuel pump as it runs over the top. So there's a reasonable chance the wiring may have been damaged in the process.

Can someone tell me the best way to test both the wiring and plug please? I have a multimeter. Eg. Is there certain voltages on certain pins? Can I test the sensor itself with a magnet and continuity?

I'm not too worried as everything seems to be running OK but if it's something that should be looked at I'd rather do it sooner than later.

Many thanks

[RichardW]

What engine?

[MixerFistit]

2.0 HDi (RHZ) - mk1 dispatch face-lift 2006

[RichardW]

Did you have the sensor out? I have a dim recollection that the air gap is critical.

[wheeler]

It must be seing the sensor signal otherwise the engine wouldn't even start. The cam sensor signal on this engine is only used for initial starting, once the engine is running it doesn't use the signal for anything.
Is hall effect sensor so the only proper way to check it is with a scope. You can at least check the 12v supply & earth.

[MixerFistit]

Did you have the sensor out? I have a dim recollection that the air gap is critical.

No, haven't touched the sensor itself, I only unplugged it to move the harness forward and away from the pump, although I stress I don't know how long this code has existed for so it may be a red herring.

It must be seing the sensor signal otherwise the engine wouldn't even start. The cam sensor signal on this engine is only used for initial starting, once the engine is running it doesn't use the signal for anything.

Maybe the air gap mentioned by Richard changes with thermal expansion? Although I guess the van wouldn't start when warm then and it restarts perfectly fine whether 85° C or -5° C as tested in the last chill.

The freeze frame states:
Engine speed 2538 rpm
Coolant temp 32° C
Vehicle speed 34 kph
Actual flow 57 mm3/stroke

I've seen a method for testing the sensor using a voltmeter on the data line and something ferrous but I'm also wary of opening a can of worms and turning an invisible fault into a non starter if I go poking.

Also came across an old interaction with a member and Wheeler. It only seems to raise questions though as what the member achieves doesn't make sense. Could this simply be a ghost fault linked to something else?
viewtopic.php?t=50246

[xantia_v6]

I recall (but may be thinking of a different engine) that if the ECU detects a fault in the cam sensor, it tries both of the possible timing points relative to the crank sensor and lets the motor start and run normally, with the only visible symptom being that the engine cranks for several revolutions before starting.

[wheeler]

I've seen a method for testing the sensor using a voltmeter on the data line and something ferrous but I'm also wary of opening a can of worms and turning an invisible fault into a non starter if I go poking.

This is only a very basic sensor test like if you suspected the sensor was completely dead, if you wave a piece of ferrous metal past the sensor when the sensor is powered up you will see the signal output changing from 0v to 12v. The problem is your engine is starting so it would be highly unlikely this test would show anything wrong. This is why you would really need to check it with a scope as this can pick up the signal dropping out even for a split second.
As for the running, try it yourself. Start the engine up then unplug the sensor, take it for a drive & i bet it runs completely normally although it may put the engine management light on. If you then turn the engine off it will not re start again till you plug it back in.

[MixerFistit]

I recall (but may be thinking of a different engine) that if the ECU detects a fault in the cam sensor, it tries both of the possible timing points relative to the crank sensor and lets the motor start and run normally, with the only visible symptom being that the engine cranks for several revolutions before starting.

That's interesting. How long would you say for? I've always thought it cranks for a little too long but don't have a reference. I have an over specced starter after the old one failed so it cranks very quickly and has turned over within a second so it's certainly not something I've ever worried about but it does sound like a few revolutions have been made. I just assumed it was fuel pressure building.

And by fault, I'm assuming this is the kind of fault that allows it to still register something. My fault is "No signal" (presumably that's intermittent), but when searching I did come across the same fault labelled as "Incoherence" which would better fit with what yourself and Wheeler are pointing to.

I'm not certain how Hall effect sensors work but know they're used in ebike throttles so I guess they probably send pulses (pwm?) rather than modulate the voltage hence the need for a scope.

It's starting to be a bit more tempting to load the parts cannon for a single shot seeing as the sensor doesn't seem too expensive. Are these recommended as dealer only or copies OK?

Edit, Marc provided the part number for me (1920ES) but is not available from Citroën anyway.

[MixerFistit]

Just to add, I just recorded a cold start and it does 4 cranks in less than one second before turning over, so I'm going to guess that's perfectly normal for a 17 year old 2.0 HDi