Vauxhall Astra G Petrol (1998 - 2004) - 2000 1.8CD engine management fault

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Mon 18 Aug 2008 23:22
2000 1.8CD engine management fault - SpockII
I have a re-occurring fault with the engine management light coming on/off whilst driving.

When engine hot and over 60mph and on motorway and at cruising speed the light comes on.

When I accelerate with lack of power at this point the light goes out after a while.

The codes revealed knock sensor faults on all cylinders.

My local garage reset and they returned, so had knock sensor replaced, fault still exists.

Engine has also become noisy, is regularly serviced and currently at 65,000 miles approx.

I had a full service 8,000 miles ago and do approx. 20,000 miles per year.

The garage is suggesting changing the oil?

Any ideas?

Edited by SpockII on 18/08/2008 at 23:24

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Mon 18 Aug 2008 23:34
2000 1.8CD engine management fault - Number_Cruncher
Get the garage to thoroughly check the oil circuit, including;

the oil pump/block gasket - these can fail suddenly between bolt holes, losing pressure
the oil pressure relief valve isn't stuck open
the function of the oil pressure switch
to check the oil pressure using an independent gauge
to remove the cam cover, and check that oil is getting to the top end of the engine, and is filling the followers, and coming out of any oil holes in the cam as it should

It's not unknown for either the internal gear on the oil pump, or the hexagon drive on the crank nose to fail.

In short, it sounds like the knock sensor is correctly hearing knock; but that knock is mechanical rather than combustion based. So, when the ECU retards the ignition timing, the knock doesn't go away, and so, once full retard has been applied, the engine management light comes on.

I've seen this a few times before, and it's probably yet another case of a mechanic misinterpreting a trouble code as an electronic component failure, when, actually, the electronics are working quite correctly.



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Mon 18 Aug 2008 23:36
2000 1.8CD engine management fault - Screwloose

I'd suggest an urgent oil level and pressure check; the code may be only a symptom of something much more serious going wrong.

If the knock sensor picks up high-frequency noise that the ECU can't stop by progressively retarding the ignition on each cylinder individually, then it will set knock sensor codes.

As always; the garage shot the messenger.....
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Tue 19 Aug 2008 21:48
2000 1.8CD engine management fault - SpockII
Thanks all I am having an oil change planned for thursday but will talk to the garage and suggest issues raised by you both. I shall check the oil level tomorrow.
Today after warming up due to knocking I have limited power an car is too slow to overtake even a bus or lorry so timing is fully retarded.
Will let you know outcome.
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