The Camshaft Sensor Error.

2tall2slow2

Guest
Hello everyone.
Ive read through the forums in relation to this error and im still confused how this relates to the problem im having. This will be a long one so please bear with me as i want to list everything as it may be relevant.

My car is an 04 Leon Cupra Tdi. I use it for work clocking approx 500 miles a week so its maintained well, serviced regularily etc. It has 68k under its belt.

About 2 months ago i started getting that beep and light from the cooling/temp gauge when the car was 1st started for the day. Thought nothing of it as it disappeared after a restart.
6 weeks ago the car had a full service but still had the temp warning first thing in the morning.
About 2 weeks later the Pollution/Diagnosis light came on and stayed on. Due to the mileage i booked it in for a cambelt change and water pump replacement at a non dealer garage hoping the coolant and pollution warnings were pump related. They have done all the work on the car post warranty and ive used them for all my cars for years and been very happy. The car was booked in on a wednesday because the guy who was doing the cambelt change was going on holiday on thursday. Mid afternoon wednesday i get a phone call saying they have had a problem getting hold of the pump and it wouldnt be finished till thursday afternoon. I picked the car up on thursday. Brilliant. No coolant/pollution warning. Ran superbly. I did a 20 mile trip, parked up for a couple of hours then did the return trip and no problems whatsoever.
Yesterday morning i went out and tried to start the car. It turned over but wouldnt catch. Nothing helped. Occasionally i would get an oil warning and the diagnosis light came back on. Called the AA. The guy who came out was excellent and really seemed to know what he was doing. He had all the diagnostic equipment and spent 2 hours trying to get the car to start. I told him the history above and he checked everything including timing etc. He cleared the codes and kept getting the same error. Cambelt Sensor Error. As the sensor had been changed as part of the cambelt kit i suppose the natural thing to think is that the garage have misaligned the belt but apparently that was fine.
Eventually the AA guy gave up so i rang the garage and they said bring it back to them. 20 minutes later i get a phone call from the garage and they say the car is starting ok. They had done nothing to the car apart from the AA guy explaining to them what he'd tested etc. All they did was push the car into the garage in preperation for having a look at it today and one of them decided to give it a go.
I went and picked the car up because the garage said there was nothing else they could think of and that it must be some sort of wiring/ecu fault. When driving back everything looked ok and again it drove beautifully but now the airbag warning light has come on and stayed solid.
Of course, when i tried it today, it wouldn't start and the diagnosis/pollution light is back on as well.
As far as i understand it, the car wont start because of the Cambelt Sensor Error which is logged hence the diagnosis light . If the sensor is new and the cambelt and timing is ok is it a wiring/ecu fault?
All im looking for is some sort of direction on where to take the car next or even better that its a known fault. I dont have a local SEAT dealership so i'll have to go to a VAG specialist as its going to be an AA tow job.

Many thanks for reading.
All the best
Rob
 

Muttley

Catch that diesel!
Mar 17, 2006
4,987
31
North Kent
Here is what VAG says about this sensor. It isn't a cambelt sensor, it senses the position of the camshaft, an important parameter for the PD engine.
____________________________________________
Sensors
Hall sender G40

The Hall sender is attached to the toothed belt guard below the camshaft gear. It scans seven teeth on the camshaft sender wheel attached to the camshaft gear.

Signal utilisation
The engine control unit uses the signal which the Hall sender generates to recognise the cylinders when starting the engine.

Effects of signal failure
In the event of signal failure, the control unit utilises the signal which the engine speed sender G28 generates.

Cylinder recognition when starting the engine
Since the camshaft executes one 360° revolution per working cycle, there is a tooth for each individual cylinder on the sender wheel; these teeth are spaced 90° apart. To enable the teeth to be assigned to the cylinders, the sender wheel has an additional tooth for cylinders 1, 2 and 3 with different spacings.

When starting the engine, the engine control unit must know what cylinder is in the compression stroke in order to activate the correct pump injector valve. For this purpose, it evaluates the signal generated by the Hall sender, which scans the teeth of the camshaft sender wheel and thus determines the camshaft position.

This is how it works:
Each time a tooth passes the Hall sender, a Hall voltage is induced and transmitted to the engine control unit. Because the teeth are spaced at different distances apart, the Hall voltages occur at different time intervals.

From this, the engine control unit recognises the cylinder and can control the correct injector solenoid valve.

____________________________________________


These Hall effect sensors are very reliable, so I'm surprised that it was changed as part of the cambelt change. I'd have thought that the act of disconnecting and reconnecting the sensor plug is more likely to generate problems, plus you get an uproven sensor.

The sensor is right next to the camshaft sprocket, and the sender wheel is underneath that sprocket, closest to the head. It shouldn't have been disturbed during the cambelt replacement.

First thing I'd check is the sensor connector itself. make sure it's clean and then reconnect it solidly.

As it says above, once the engine is running the ECU can use the engine speed sender, but at startup it must know which pump is about to inject, and so has to know the absolute position of the camshaft.

If the connector isn't the problem, the ECU and the sensor need testing by VAG diagnostics machinery. If you had the old sensor, I'd suggest trying to refit that first of all, to eliminate the new sensor as the cause.
 
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2tall2slow2

Guest
Very possibly.
Something i just remembered. The AA guy said that sometimes he was getting the correct voltage on the points he was checking in the engine bay and sometimes it just wasn't there
 

seremotors

Dave the Parts Manager
Mar 11, 2008
12,507
9
Belfast UK
www.seatcupra.net
tbh i would spend £20 on a new sensor even for elimination purposes. they give grief right across the range and send signals to the gauge and to the ecu. vas5051 or vagcom should be able to check what temp it reads and common sense should tell if its close or not. also seen a few engine wiring plugs with green corrosion on the pins, might be worth a check
 

2tall2slow2

Guest
Well. I took it to Seat and it turns out the cambelt timing WAS out :censored: and I also had a cracked intercooler pipe.
Has anyone got any advice on getting some of my costs back from the garage who originally fitted the new cambelt?
 

2tall2slow2

Guest
Well, the plot thickens. Car has been running fine until Friday I noticed an oil leak. Parked up and the leak stopped soon after. Finally got the car to a local garage hoping it was a quick fix. Mechanic got it up on the lift and the oil looks like it's coming from the head gasket. There's also smoke coming from the oil tank which the guy said is a sign of worn piston rings.
Is any of this right and is any of it linked?
I'm a complete novice to this but i am shocked all this can happen to a tdi that only has 69k on the clock :confused:
 
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