S80 Fuel Pump Relay Question

[zeiglerr]

I found that a temporary fix for this problem was to remove the horn relay and wire a separate horn button, but I FINALLY found a permanent solution. The cause (which I discovered on a European Volvo discussion board) was that the rechargeable batteries in my siren module were failing and had trashed the circuit board. Volvo gives the siren module a useful life of 6-8 years. When the board gets cooked from either battery leakage or high heat/resistance, it sends confusing signals down the CANBUS that make the system think the car is being stolen or that it has been in an accident - thus shutting off the fuel pump relay. I replaced the siren module (about $260 from AutohausAZ) and all of the problems went away

Here are some photos of the circuit board. The damage is where the battery pack plugs into the board. Hope this saves someone else hours of diagnostic time!! It's also important to note that the dealer didn't catch this and wanted to start by replacing expensive modules to isolate the problem. -Reid

[BEARYBEE]

So I have a 99 VOLVO s80 T6 with a similar problem. One day running great. Started it, it stumbled and stalled. Started again....started right up. Ran 8 miles. No issue. Went to start again-no fuel pump. Switched relays with fog light under the dash-no power. Pulled the fuel pump and bench tested - it was okay. Spun up no issues. Reinstalled and left out of tank and cycled key-no power to the pump. I left the car sit for a few days and went back to it....reinstalled the pump and got it into place, i was going to short the relay but before I did that, I tried to start and bam...the pump came on and the car started. Let the car run for a bit to charge battery. I shut the car down and restarted it a couple of times...no problem. 45 minutes later I tried to start it and it would not start. I have no messages on the info screen, I tried a different key...still would not start (no fuel pump). I shorted the relay to bypass and that did not work. Am I doing this correctly? The relay is located to the right of the fog light relay under the dash. I had to remove two torx screws to get to this panel. I am taking a wire and shorting the two lower horizontal lugs.