engine management light, intermittent fault!

[pnfootitt]

Hi guys, perhaps somebody has had this fault before and can help me, the engine management light comes on after start up when hot, after the engine has been turned off for ten minutes or so, i used a lexia3 to analyse it, and it says under intermittent faults:-
" Control of the turbo piloting valve short circuit to -ve or open circuit" i dont know if theres a part two to the lexia which explains what that means, or anybody knows the answer, many thanks in anticipation.

[spitroen]

I have that engine light on too, but don't expect any answers here soon.
The wind is whistling over this site.......

[noz]

pnfootit,

Can you remind me what engine you have? Maybe you could put a note of it in your signature for future reference (please see my signature below for reference).

As the text for the fault suggests, the valve which controls the wastegate on the turbo is either open circuit or short circuit.

Unlike the diesel turbos which have purely mechanical wastegates, the petrol engines have motor controlled wastegates. Having said that, having had a quick look through the wiring diagrams I can only see one engine with a motorised wastegate valve, the XU10J2TE with a Bosch MP3.2 ECU i.e. the 2litre Turbo. None of the others seem to have one on the wiring diagrams which suggests they are also mechanically operated like the diesels(or don't have turbos). (I only have diesels do can't confirm first hand. Maybe someone else can?)

I can't tell from the wiring diagrams if the wastegate control is an electric motor directly connected to the wastegate or if the wastegate is pneumatically operated with the motor symbol actually representing a variable orifice valve on the vacuum line leading to the wastegate actuator. Whichever it is, the cable connected to it is grey and grey/white. The connector is black and two-pole. I have no record of the expected resistance. However, I suggest checking the resistance across the valve/motor and it will soon be obvious if it is out of range (the fault suggests infinity or zero respectively). If you measure it and it is indeed faulty then you will need a new wastegate actuator motor.

If the motor/valve tests out OK then an alternative line of enquiry would be both the power feed to the motor/valve and the earthing via the ECU. THe power for the motor/valve comes from the double injection relay. With the engine running the fed to the motor/valve should be 12v (or battery voltage). The voltage on the earth side of the motor/valve will vary depending on how much current the ECU is allowing to flow to earth. At idle the boost valve should be fully closed so I would expect the ECU to permit no flow of current and therefore the earth side of the motor/valve would also read 12v. As the pressure rises in the inlet manifold the MAP sensor will signal to the ECU that the pressure is high enough and to begin dumping air through the wastegate. At this point the ECU will permit current flow through the motor./valve and the oultet voltage will fall eventually reaching zero when the wastegate is fully open.

I hope that helps. If you need more help carrying out the actual testing then please just come back with any questions.

cheers

noz

[bigjohnh]

The wastegate on the 2.0 turbo is still mechanical, the electronic control is used to bleed off feedback pressure and so fool the wastegate that the pressure is lower and keep it closed for longer. The valve is (I think) a solenoid valve which is either open or shut and the control is achieved by pulsing the signal to the valve. Signal on=valve open. The system fails safe so the bleed off is not activated and the waste gate limits the boost safely just like the diesels.

As Nos correctly states the failure modes are either short circuit or open circuit and this is the best place to start testing.

John

[pnfootitt]

Thanks everybody, Noz you were spot on , thats the car, and it was the turbo control valve, sits at the back of the engine, i thought it was part of the windscreen wash system!!!!, it cost £72 from citroen, and all is now back to normal. many thanks

[pnfootitt]

engine management light on----- 9 times out of ten that will be a fault with the lamda sensor, (£60), i did change mine, but it didnt cure it which led me to buying the lexia diagnostic tool, and it pointed to the faulty valve, just the french using the word "piloting" was confusing, it meant "control".
when that light comes on, the ECU goes into default mode, a rich setting, which will cost you fuel until fixed!!

[noz]

pnfootitt,

No problem. Glad to hear you got it sorted. Well done.

cheers

noz