S40 (New) Electrics : Temperature sensor fault

[Northview]

A month or so ago, I suddenly noticed that the temperature sensor in my S40 2.0D SE was displaying an outside temperature of -20 degrees C. The actual outside temperature at the time was 18 degrees. I pulled over and switched off, but when I restarted, it was still reading a ridiculous sub-zero temperature. Over time, it gradually increased towards normality, but was still sub-zero by the time I parked. Later when I got in the car to drive home, it was reading normally again.

This morning, with an external temperature of around 14 degrees, the display was reading --C (presumably it thought it was so cold it was below the range of the sensor!). After a few miles, it struggled up to -40 and with a few adventurous surges as high as -35, there it stayed.

Irritating, but not a big deal in itself perhaps...except that the climate control assumed that since it was so incredibly cold out, it would have to put the heat on full blast to compensate, so before long it was overpoweringly hot in the car. Switching to manual control for the fan mitigated that a bit, but it was still pumping hot air in through the vents. I ended up driving with the windows and roof open to keep from getting cooked. Then it occurred to me that if I dialed down the air-con to minimum (Lo), it would be on continuous full cooling instead. That worked, but still meant I had a choice of being cooked or being frozen.

I took it to the dealer who told me that "it sounds like a problem with the external temperature sensor"...which didn't exactly come as a surprise to me! However, nobody was available to look at it. The best they could do was book it in to be looked at next Tuesday (today is Friday). They can't supply a loan car either.

Yet another problem with this car - they seem to be endless. I'm not at all impressed with it, or with the dealership. I'm now seriously considering selling up and getting something else, even though I would normally expect to keep the car for at least 3 years (I've had it for 18 months).

[humpy999]

Given that there is also a sensor inside the car to tell the AC what the inside temperature is, why would an external temperature sensor fault cause it to overheat inside?

[nano]

The controlling system is quite clever to adjust the amount of heat needed to maintain the inside temp to the selected with a given (measured) ext temp,

but it is completely damp to figure out that the -40 is due to an error

[bircham]

Heelo,

My wife's V50 had exactly the same fault. The dealership replaced the wiring loom inside the wing mirrors (it also fixed the fact that her mirror wasn't defrosting either. The dealership should know all about it - ours wasn't surprised to hear about our problem and knew exactly what to do,

Jon

[Paul Clifton]

The ambient temp sensor is located in the n/s door mirror and there is a known problem with the 'a' pillar electrical connectors on these models. If you open a front door it is the connector you can see between the door and body near to the check strap. This wiring supplies all functions to the doors ie lock/unlock, window lifts mirrors ect any probs with any of these suspect the connector. The fix is to replace the wiring looms in the doors and the car which have connectors with gold contacts to prevent corrosion of the terminals. Freebie if car under warranty.

Paul.

[alybongo]

Thanks Paul, Whipped out the rear connector cleaned up the points reconnected - Bob's your uncle working again.


Alistair

[Northview]

Originally Posted by pc654

The ambient temp sensor is located in the n/s door mirror and there is a known problem with the 'a' pillar electrical connectors on these models. If you open a front door it is the connector you can see between the door and body near to the check strap. This wiring supplies all functions to the doors ie lock/unlock, window lifts mirrors ect any probs with any of these suspect the connector. The fix is to replace the wiring looms in the doors and the car which have connectors with gold contacts to prevent corrosion of the terminals. Freebie if car under warranty.

Useful information, Paul. Thanks. I did have the car booked in for last Tuesday, but as it turned out I was sick and couldn't get to the dealership. I'm inclined to leave it alone for now, since it's currently working normally again, but if it goes on the blink again, I'll try cleaning the connectors, etc.