Guys,

I'm having a problem with the engine management light in my wife's Mk2 Fabia. It's a 57 model, BBM engine, 105,000 miles on it. Full service history, generally very reliable.

Last week it produced a check engine light so I read the codes and it came back with a P0341 Camshaft Sensor error. I cleared the code but it was back within a day or so.

I bought a new camshaft position sensor and swapped it in, and reset the engine light. All was well, but the code and light were back again a couple of days later (i.e today), plus reports of the car 'not running right'.

I've just cleared the code and taken it for a drive. Code and light are back almost immediately, and the car definitely isn't right; it's lumpy to drive, slow to start (it usually starts very crisply) and seems down on power.

Clearing the code again and leaving the cam position sensor unplugged makes it still drive lumpily but the light stays off. (Yes, you read that right.) Plug the sensor in and the light comes on again.

I've swapped the sensor back for the old one and the light has stayed off for a bit so I'll see how things go. The huge snag is that the car is booked for an MOT tomorrow morning and an engine management light will make it fail. I'm therefore hoping that the light will stay off for long enough to pass the MOT.

If anyone has any wisdom then I'd love to hear it. FWIW, the P0341 code appears twice - once as 'active' and once as 'pending'. Clearing them both makes the light go off. I've checked the wiring to the camshaft position sensor and it doesn't seem damaged (rubbed/frayed/snapped).

I think the key question is whether I have one problem or two - i.e is the lumpy running related to the light? It could be a separate thing, and the lumpy running being caused by a failing coil pack (for instance), or they could be the same problem with different symptoms. Logic would suggest the latter, but they light/code appeared a good few days before the lumpy running. It could be a coincidence but it has been VERY hot this week so the lumpy running could be fuel vaporisation in the lines, perhaps?

Any thoughts, suggestions or otherwise please let me know. Thanks.

Might be the timing thats slightly out. Not sure if its a chain or belt on yours but if its jumped a tooth it would explain the poor running unless the new sensor is either not working or compatible? Another option according to rosstech vcds is that low oil or oil pressure can also ping up the same code?

copied from rostech

Possible Symptoms

• Malfunction Indicator Light (MIL) active

Possible Causes

• Wiring from/to Camshaft Position Sensor (G40) faulty

• Camshaft Position Sensor (G40) faulty

• Timing misaligned

• Low level oil or low oil pressure

Possible Solutions

• Check Wiring from/to Camshaft Position Sensor (G40)

• Check Camshaft Position Sensor (G40)

• Check Timing

• Check Oil level and/or Oil pressure

Alasdair

Edited 22 June, 202522 Jun by Alasdair1
added further info

Hi Alasdair,

Thanks for your reply to this question. It's been a while ago now that I posted it but things have progressed ever so slightly.

I've tried a third cam position sensor and the symptoms remain the same; the light stays off for a few days when the code is reset but comes back within a week. And the car occasionally runs a bit 'funny'. I've driven the car a bit more of late and thus can offer some first-hand experience; it is occasionally a bit slow to start (it normally fires on the first time past TDC but will occasionally need three or four revolutions to start), plus it occasionally seems fractionally lumpy under acceleration.

Given the physical symptoms AND the code/light I guess there could be something amiss with the engine. Which is a pain. Oil level is fine (and checked regularly), although I have no way of checking the oil pressure. It's a cam chain engine and if that's jumped a tooth then the problems would be constant with an immediate light, rather than transient with an occasional light.

I guess the question then is what can I now check - is there a procedure for checking the engine timing? Or should I be connecting up some kind of external oil pressure sensor to see if that is dropping?

Thanks for your help.

Another thought; can I get an oil pressure reading via the OBD2 port? I have a not-entirely-basic scan tool so perhaps I could plug that in and see what live data it offers.

7 minutes ago, zcacogp said:

Another thought; can I get an oil pressure reading via the OBD2 port?

No.

There's no pressure sensor, just a pressure switch.

That's either on or off, earthing the wire that goes to it, or not, either side of its threshold pressure.

Chain timing checking is a bit awkward on this engine, really needing the locking tools to be fitted in place of crankshaft and camshaft sensors.

Cam sensor is very easily removed, crank sensor is far from easy to access.

Might be worth checking wiring continuity/connectors from camshaft sensor backwards in case wiring is failing or broken/not making good contact. You could do the same for the crank sensor. Think from memory its hidden behind oil filter area.

Alasdair

Crank sensor is round the back of the engine block on the htp engines. Approx where this ring shows:

Update on this one although no real progress.

I had a decent few hours with the car today without it being used (sounds weird given it's my wife's car but I seem to spend very little time in the same place as it when I have time to work on it!) Stripped out the intake system to see the wiring up to the ECU, which is mounted in the top right hand side of the under-bonnet area. There was nothing that looked at all amiss with it. So I had as good a look down the back of the block as I could to see if I could see the crank sensor (thanks for the photo Breezy_Pete), and all I can say is that it's a long way down and will be a PIG to get to. I couldn't even see it, although I might have been able to touch it with the ends of my fingers (although I'm not sure). I saw what I think are the wires going to it and - again - they look fine. Given how hard this will be to get to (impossible from below, equally impossible from above, and I was seriously thinking about removing the inlet manifold to see if that helped things) I'm sincerely hoping that this isn't the problem.

The only thing I could see that was remotely as it shouldn't be was the top ECU holding clip was broken so the ECU was a bit loose. I fabricated something a bit better (which might have involved cable ties) and re-assembled. I cleared the codes from the ECU so the dashboard light isn't now on and it started fine. As an experiment, I also tried removing the cam sensor entirely so I could see down the hole when the engine was running, and it ran almost as well without the sensor as it did with it (and no lights came on.)

Reading around, it seems that a failed cam sensor will allow the engine to run but it takes longer to start as the cam sensor gives a TDC reading to the ECU. However a failed crank sensor will cause the engine to not run. I can't vouch for any of this, it's simply internet sleuthing, but if it's true then it points to a cam sensor problem rather than a crank sensor problem, OR aforementioned oil pressure sensor/switch.

I'll leave it for my wife to drive for a few days and see if the light comes on again. I am very confident it will, so the next question is where is the oil pressure switch and is this worth looking at?

Thanks for your input chaps. I have the feeling that this could be a fairly simple failure that just needs to be chased to ground. At least I'm hoping that's the case!

Yep, crank sensor is 'orrible to get to. Even with intake manifold off, it can be problematic if the alloy block has corroded with that white oxide which can tighten the fit of the sensor to the point of being a right struggle to withdraw.

Oil pressure switch couldn't be much more accessible though:

Can't personally see how it could be relevant though.

On my HTP engine I did not have to remove the inlet manifold to get at the crank position sensor. I got away with undoing the (5 I think) bolts that hold the manifold to the head and then pushing the manifold against the bulkhead. There was enough flexibility in the wiring and hoses etc. to be able to reach down to the sensor without having to do any more dismantling.