Bulb failure warning light on at start up goes off when brake pressed

[marwood82]

hi,

when i start my 98 v70, the bulb failure warning light stays on after all the other lights go out once the engine is running, but then switches off as soon as i touch the brake pedal.

i've had the car about 12 months, its always done this.

is it normal?
its an auto (dont know if that is relevant)

Simon.

[scot850]

Have you had someone check your lights when the car engine is running to make sure they all work as they should? My suspicion is there is a short or bad earth in the system. Also check the high level brake light for operation. Also check the wiring harness in the tailgate LH hinge area for broken wires and shorts.

Neil.

[marwood82]

i've had a look a few times and the lights look ok,

whats got me confused is that if there was a fault with the lights then i would have thought it would stay on all the time?

its that it goes out the second i so much as touch the brake pedal that is odd.(i should point out, this warning light is on when the headlights are all off)

a short somewhere sounds interesting, as i'm having a battery drain problem that i cannot pin down.

[marwood82]

actually the more i think about it the more this makes sense.

ive had a mystery battery drain since i got the car. tried every method i can think of to track it down and still no idea whats causing it.

but this could be it.

if go to the main 60A fuse box and pull fuse 7, then the drain stops.
fuse 7 powers 5 fuses in the secondary box. one of which is fuse 13 - the lights.

now for this warning light to stay on, it means that the cars systems have detected that the current from one of the lights isnt what its supposed to be.

the thing is, when i start the car, none of the lights are on,so surely theres no reason then for this to trip at that point unless it thinks one of the lights is on?

now given that it goes out the second i touch the brake pedal (ie the second the brake lights come on),
that would suggest its the brake lights that it thinks have the problem

since the lights come on ok, that would imply the clusters and bulbs are working.
also the fuse shows no sign of wear so i would have thought that that combined with working lights would suggest that i dont have a short.(i tend to associate shorts in the lighting circuits with melted fuses)

which to me points to the brake light switch.

i.e its leaking/not disengaging properly so its draining the battery when the ignition is off and when the car starts up,
the computer sees current on the circuit, but way less than its expecting and so assumes the lights have failed. then when i press the pedal, everything 'lights up' properly and it clears the error.

does that make any sense?

[misha]

It's NOT short!
Every of these cars with automatic transmission are doing this because you're supposed to keep the brake pedal pushed every time you start the car with auto transmission.

It behaves perfectly normal.

[erikv11]

@ misha, unless this is specific to the Euro market, I would say it is not normal. None of my P80 cars have ever done it, all are/were auto transmission.

The slow drain theory could make sense up until you release the pedal, then by that theory I would expect the warning light to go back on. But still, you could be onto something. Have you checked how many amps (mA, actually) there are through the + cable with the key off?

Many behaviors like this have been traced to corrosion in the bulb sockets in the tail lights, I would definitely check there too.

[misha]

@ misha, unless this is specific to the Euro market, I would say it is not normal...

All 850s and s,v,c,xc70 with auto transmission are doing that,including mine from day one.
This is 1st time i hear that it's market dependant...however these cars with auto transmission for EU market don't have that shift override button in upper right corner of shifter like U.S market ones....so it's possible that it's market dependant.
Also U.S market cars didn't had chipped keys until '99 for these cars while we have them back in '96.

@erikv11....
I just saw that marwood82 is from Germany....so it's completely normal behaviour for EU car.

[erikv11]

I just saw that marwood82 is from Germany....so it's completely normal behaviour for EU car.

Yeah I saw Germany too ... I think you have solved the mystery.

Unfortunately OP still has to track down the parasitic battery drain.

[marwood82]

I just saw that marwood82 is from Germany....so it's completely normal behaviour for EU car.

Yeah I saw Germany too ... I think you have solved the mystery.

Unfortunately OP still has to track down the parasitic battery drain.

oh well, it was a nice theory while it lasted

at least i know now its supposed to do that

[erikv11]

Guten tag!

Get a voltmeter in series on the positive cable, then start pulling fuses one by one - have you tried that yet?