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Ford Focus immobiliser fault in hot weather

Our Focus (2001) has developed an intermittent fault in that it won't start on occasions which seem to be when the ambient temperature (not the engine!) is very hot. The PATS LED which is flashing slowly as normal when you get in goes out when the key is turned rather than coming on for about three seconds. Everything is completely dead. After a while, which may be 5 mins to an hour or more, it does start, which I guess is when the car has cooled down.

It would appear that either the transceiver is not reading the code from the key or, if it is, the immobiliser is not getting the go ahead to allow the engine to start. It happens with both keys so I guess it rules them out.

We've had it in a main dealers who did a diagnostics check and, I guess as a result of that, replace the transceiver. A week later, on the first really hot day since then, the fault has re-occured.

Two questions: Firstly, has anyone come across this fault before?

Secondly, I can imagine the bill will start to increase, particularly if the PATS system needs replacing, etc. If this is the case, can I just have the immobiliser bypassed? I realise this reduces the security of the vehicle but I guess I could just wire up a flashing LED to make it look like its on as a deterrant - and there may be insurance implications.

Cheers, Pete

Reply to
pete
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Firstly as the PATS warning lamp (if i read correctly) is going out when you power up the ignition (from it flashing slowly- i.e. immobilized state) and NOT flashing quickly, then the ECU is reading the code from the key fine. This rules out problems with the ECU, the transceiver and the key.

When you say its dead- do the dash lights come on? I am assuming they do, but you have no starter action when you turn to position II. ?

If you have NO dash lights, then you have a break in the wire from battery >

engine bay fuse box > main fuse > ignition relay > ignition switch which should be fairly easy to determine. Most likely its one of the main relays with a dry joint which is opening up in hot weather.

Check the earth straps whilst you're at it.

If the ECU failed to receive a code, or an inncorrect code from the key, then the PATS light would be flashing quickly.

Tim..

Reply to
Tim..

Thanks for the reply Tim.

When the car is working normally, the PATS warning LED goes from slow flashing to a steady light for about 3 seconds when the key is turned and then goes out.

In the fault condition, the slowly flashing LED goes out when the key is turned and remains off (there is no rapid flashing which, as you pointed out, would indicate that the code is incorrect). Also, in the fault condition, the dash lights do come on but there is no starter action.

Any further thoughts?

Reply to
pete

Thanks for the reply Tim.

When the car is working normally, the PATS warning LED goes from slow flashing to a steady light for about 3 seconds when the key is turned and then goes out.

In the fault condition, the slowly flashing LED goes out when the key is turned and remains off (there is no rapid flashing which, as you pointed out, would indicate that the code is incorrect). Also, in the fault condition, the dash lights do come on but there is no starter action.

Reply to
pete

Thanks for the reply Tim.

When the car is working normally, the PATS warning LED goes from slow flashing to a steady light for about 3 seconds when the key is turned and then goes out.

In the fault condition, the slowly flashing LED goes out when the key is turned and remains off (there is no rapid flashing which, as you pointed out, would indicate that the code is incorrect). Also, in the fault condition, the dash lights do come on but there is no starter action.

Reply to
pete

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