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Why does the stop light come on? The other day I was driving at a fast speed when the stop light came on, it was a hot summers day and i noticed the air con stoped working at the same time. I drove home thinking i would take it to the dealers when the next morning it wasn't on anymore and the air con is now working. A couple of days later on the motorway it came on again and again the air con ceased to work.

Has anyone had this problem and knows if it is expencive?

Stop light is ECU controlled and is linked to any of the following...

Coolant temperature
Coolant level
Oil pressure
Oil level

As the AC went off, my guess is it's temperature related so check your fans work and that your coolant is topped up.

The A/C will indeed be shut down under load or rising coolant temps.

I would check the coolant system, altough the expansion bottle may be full it doesn't mean the system has been vented of air properly.

There should be a vent point on the thermostat housing and one on the hoses feeding the heater matrix just before the bulkhead.

You will need to frig up another bottle on top of yours to assist with expelling all the air and displacing it with fluid.

I use an upturned drinks bottle with a rubber seal against your expansion bottle opening and with the help of another you can fill the bottle past it's filler neck and then vent the system out.

Ive been monitoring this a bit closer and it only comes on at about 72 degrees c. I just had a new radiator fitted by a peugeot dealer and it was doing this before. I notice i can hear the fans working, i have the right amount of oil and coolant in. But its good to hear that it is something to do with heat.

You had this problem before the new radiator was fitted?

If so then what was the reason for the radiator? It could be a dead thermostate as 72degrees is far from two hot.


Dan

There was a tiny hole in the bottom of the radiator, and taking a close look there was corrosion at the bottom of the radiator. The thermo seems to start normal, at 72degrees the light comes on but the the temp goes upto about 90, the starts to cool down again.

Would you believe it, the stupid stop light is not coming on now and a/c is also working fine. Since ive had this car, which is only 5 months- im expecting something to break every month...

As I started to hope it wouldn't come back, it did. 72 degrees stop light on and air con off. Could anyone tell me how the aircon is connected to the engine? Could a problem with the aircon system also cause the stop light to come on?

If it was me I would consider going to a Pug dealer for a 'Global Test' (diagnosis).

I would guess it is a simple fault with a sensor but finding it yourself could be a nightmare without the right kit.

The stoplight will turn off the A/C as it thinks the engine is running hot and needs to save on extra loads IMO.

I can't see how the A/C will bring the stoplight on myself, the cars ECU controls the A/C, not the other way round.

cheers pal, does it cost for a diagnosis. And what is a imo?

I;ve had this happen as well, It was the Fan control box under the N/S wheel arch, You can always test the fan's by taking off the Brown plug on the stat housing above the gearbox, the fan's should come on.
A diag test at the dealer's wouldn;t show this up

Cheers pal your right, I did take it in and it didnt show on diag test. The fan was staying on too long and coursing the light to come on, it was some sort of relay switch like what you said.