Right, had the code come up (cheap code reader) for coolant temperature sensor.

Changed it, started with a cheap one.

Still had the problem.

Changed for a Genuine one.

Still got the fault.

Have since purchased VCDS.

Ran it today and got the code:

1 Fault Found:

17664 - Engine Coolant Temp Sensor (G62)

P1256 - 35-10 - Open or Short to Plus - Intermittent

Reset it, came straight back, tried again, came straight back. I have tried electrical contact cleaner, checked the wiring where visible, all seems fine.

So what else could it be?

The car will re 0 for ages (on the gauge) then slowly rise, then maybe fall, or rise, or fall, or rise.

If it is at 90, you stop the car, restart, it goes to 0 and stays there for ages again.

I read the engine temp with VCDS and it even went in to - figures.

I am stumped.

Might need to trace the wiring right back to its source. Could be a royal pain in the backside.

However, I would try one more new oem sensor just in case.

The probable causes for this code are:

• wiring open circuit/short to positive
  
• coolant temperature sensor
  

I'd be inclined to check the wiring and if all seems well change the temperature sensor.

SN

So another £30 :(

Tbh, the OEM sensor was sent from up country, new though. Damaged in transit we think?

Also, thanks for your help/ suggestions.

This will surely be a break in the wiring, within the insulation so you can't see it, and with vibration it will sometimes make contact, sometimes not.

Overwhelmingly likely to be just at the point the wires emerge from the strain-relief/cable entry of the connector.

Grab a spare connector off a car at a scrappie, with a couple of inches of wire still attached, splice in.

Will source one and try when I get some free time

Surely it will have to be either the wire or sensor, nothing else is there? Except the ECU

If you've got a multimeter you could try 'buzzing through' the wires from the sensor connector to the ECU connector, whilst waggling gently. This could prove one way or the other.