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post #1 of 7 (permalink) Old 08-18-2009 Thread Starter
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Unhappy 2004 XC90 - Both Brake Lights Out


Newbie here, but not new to playing with cars. I recently tackled replacing the fuel pump on my XC90 (known leaking issue). Everything went just fine, but I'm stuck on an issue "after" I put everything back together. I had the battery disconnected, but reconnected it to be sure the pump/lines sealed and I had no leaks. Once I was all done, I put all the seats back in and here is where the problems started. I got a SRS Alert which was my fault. The center seat SRS sensor was disconnected when I reconnected the battery and tested the pump. Here comes the SRS error code. Ok I knew I'd have to get to the dealer to reset it. But the real problem is I now have a fault code of "Check Stop lights". It seems "both" left and right stop lights don't turn on but the center bar does. All other lights/functions on the entire car are perfect. I checked the fuses and none were blown, so I am suspecting its the relay in the left rear compartent. But I can't find a diagram to tell me which relay is for the brake lights. Or is it possible I may have dislodged one of the connectors under the seats when I worked on the pump? I checked those and found nothing wrong. Just got back fron Volvo and they charged me $75 to reset the SRS code, but they wanted $300 to $400 to figure out the stop light issue. They weren't kidding so I said no thanks. I mean I didn't touch any electrical connectors in that repair except what was needed for the fuel pump. Any suggestions? I even asked Volvo to provide me with the diagram for the rear compartment relays to test the stop light relay (I have a spare), but they said "Oh, we lost that page in the service book". I take that as a pay me my $300 and I'll fix it for you lie.

Let me know. I won't drive the car without the brake lights working.

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post #2 of 7 (permalink) Old 08-19-2009
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Welcome, first what I would do is eliminate the obvious but we probably not the issue - replace the bulb with a brand new one. As crazy as it sounds if both bulbs blew for some issue you could drive yourself nuts on a simple fix. I'd put a meter on the brake light switch up under the dash to make sure you have voltage coming out and check the brake light sockets with a meter to isolate. You could have a faulty brake light switch.

Something else to try is often the electrical contacts on the removable bulb holders get dirty or partially corroded, and then don't carry current well. This can cause the Brake Lights or other Rear lights to fail intermittantly or fail completely.

1. Clean the contacts in the bulb holders and the contact areas on all the bulbs involved.
Use a small piece of emery cloth, or a piece of steel wool.
2. Check the connections where the wiring connects to the lights.
Clean away any corrosion and make sure the contacts are tight.
Sometimes you can use needle nose pliers to gently tighten them.
Replace any corroded wiring.

Let me know how all goes.

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post #3 of 7 (permalink) Old 08-21-2009 Thread Starter
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Still no Lights

Thanks for the suggestions, but the contacts are as clean as the day the car rolled out of the factory.

I ended up checking the brake relays and shunt in the rear compartment to no avail. I guess I must have somehow disconnected a connector under the rear seats when I was replacing the fuel pump. Just doesn't seem possible, but I have the wiring diagram now and will double-check them again.

Every other electrical system is unchanged since the fuel pump was installed, and again, the brake lights were working fine before I started on the fuel pump (and the center bar still lights up,just not the side brake lights)

It always seems to be something with these XC 90's.
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post #4 of 7 (permalink) Old 08-24-2009 Thread Starter
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Still no Brake Lights

I was able to secure a copy of the wiring diagram for the XC 90. I have now tried replacing all the fuses relating to the brakes, both bulbs (again), i switched the brake relay out in the rear compartment REM, I have taken out the rear seats again and doubled checked all the connections.

Nothing, zero zip. I still have the upper center bar coming on when the brakes are applied but still not the two outer lights. All other rear lights and entire electrical system in the car is functioning perfectly.

I really don't know where to go from here. I have heard that sometimes the relays need to be "woken up", but I'm not sure how to do that other that replacing it. Would having the rear compartment REM reset do anything and is that possible? Is that something I can do or do I need the dealer to hook up their computer to test all the computers?
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post #5 of 7 (permalink) Old 08-24-2009
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You will need to get a volt meter and start from one end to the other and you will find along the path where the break is.

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post #6 of 7 (permalink) Old 08-25-2009 Thread Starter
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Talking Solved - rear brake relay defective


After going over every electrical component and connector that I thought I could have damaged when I replaced the fuel pump, plus going through all the fuses, and relays, the last and final check I did was to completely replace the brake relay in the left rear compartment and PROBELM SOLVED!!!

What's really strange is that's where I actually started to look for the problem. I switched another relay (exactly the same) from my fog lights, and tried it in the brake relay location and switched the brake relay over to the fog lights. The fog lights worked but the rear brakes still wouldn't function. So I switched everything back.

Why replacing the brake relay with a completely new one did the trick is another mystery.

But, the long story is, the fuel pump replacement had nothing to do with the brake lights going out as I suspected. How the lights went out coincidently at the same time as the completion of the work on the fuel pump is why I chalk it up to "its a Volvo, what do you expect".

Thanks for sticking with me on this one.

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post #7 of 7 (permalink) Old 08-26-2009
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Congrats and thanks for the update! I'm sure it will help others who follow.

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