Hi guys, my car is doing something very weird which I've only noticed today. When you switch the park lights on, the brake lights come on too. If you have the lights off and press the brake, it works like how it should but if you switch the headlights or even just the park lights on, the brake lights come on. What could be the problem? Please help. thank you in advance

 

Hi guys, just an update, connected the vehicle to an OBD reader (Delphi). Picked up a fault for the brake light switch, opened the switch and found that the contacts burnt, I have replaced the switch and the brake lights are still coming on with the park lights, and now the OBD reader is picking up "Comparison error". Didi anyone have the fault before and/or know how to fix this? Thank you

 

The question is: what burnt up the brake switch? To you pull a trailer or anything like that where you modify the wiring? Has the car been wrecked where wires could be pinched?

 

Nope, no trailer and no modifications to any wiring. The vehicle hasn't been in any accidents either

 

I'm not afraid to make an educated guess. Comparison circuits are used to tell if a light is burnt out. One side of the car is compared to the other. If they don't match, the check light comes on. Do you have a warning light for burnt out bulbs?

So: what could possibly connect two independent circuits? Obviously the brake lights are being energized by the tail light circuit. I wonder if there is a way that a defective light bulb could have shorted across the poles? Maybe an incorrect type bulb used?

There's always the possibility of wiring damage done by rodents. I don't know about South Africa, but here in the US, we have mice that nibble on wiring because the insulation tastes good to them.

 

I totally agree with the advice given by eflexter.

 

Hi guys, thank you so much for your replies. I did have a hunch about what was wrong but didn't want to say anything until I was completely sure. I did have the car checked out by a Volvo tech and he did confirm that the CEM is faulty but luckily in a way its only a fault with the brake lights.

 

That's interesting. Usually things STOP working when the CEM dies. Mental note for the future.