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C4GP 1.8 Petrol VTR - Fuel Circuit Open Loop Fault - Help Please!

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Sat Jan 28 2012, 11:12am
Hi all,

While I was away on business, the car broke down when my wife was driving it. Car simply stopped, with the ECU light on and a Service indicator, then ran as rough as a bag of spanners at idle on restart...

Once recovered home, I went and purchased an OBDII diagnostic lead and software from ebay, and 'milked' the following codes:


Thanks to a superb list of code descriptions on this forum, I diagnosed a problem with either the accelerator pedal sensor, the Throttle Position Sensor (TPS) or the ECU/ wiring...

Today was my first real opportunity to have a good look at the car and start going through things... and I found that the butterfly return spring on the back of the throttle body wasn't doing anything due to the spindle plastic bit being snapped off. I (ahem) 'engineered' a solution to this, and the throttle butterfly now snaps back closed as it should, with the expected amount of force. I thought this was probably job-done, but on rebuild the car now won't even splutter into idle unless I manually open the butterfly. The throttle body motor isn't opening the butterfly at all.

Since this slight setback, I have brought the trusty multimeter into play...

I am getting voltage to the TPS, and manual opening of the butterfly provides a gradually decreasing output voltage from precisely +5v down to about 1.2v dc.

I have checked wiring for wear/splits/breaks as far as I can, but there's nothing obvious there. The loom to the throttle body was quite taut, so I snipped the tie holding it to the inlet manifold and eased things a fair bit. I also pared back the loom covering in that area and found the wires look okay. Wiggling them makes no difference.

I have also taken the accelerator pedal off, and tried checking for variable resistance with operation of the potentiometer. Can't seem to find that, but the unit looks in good order, and the multiplug looks as clean as a whistle.

As a last ditch I cleared the ECU fault log, and (following a couple more unsuccessful restarts) checked the log again.

There are no fault codes currently logged, but the sensor list is showing an open-loop fuel circuit.

We are a bit skint, so before I go and purchase a replacement throttle body, please could anyone shed any light on this? An I going the right way? Missing something obvious??

The car is a C4GP, 1.8 petrol, 57 plate and has done about 70k miles.

...and my back hurts.

Sat Jan 28 2012, 12:26pm

Member No: #1
Joined: Aug 07 2006
Location: Northumberland
With those error codes Premier Members can search the database and download the tech docs for them (where they exist) - Click Here -

Throttle body is one of the areas to check

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