Service Fuel System Message

Gearheaad43 · #1 (**permalink**) 01-05-07, 10:31 AM

'97 STS was fine one minute. parked it... 30 min. later had to leave again. As soon as it cranked up I got the Service Fuel System Message along with A/C off.. Blah blah and car quit.

Ran the codes.

No voltage at fuel pump.... I suspected the Fuel Pump Relay, Swapped the A/C relay with the Fuel Pump Relay and she started right up...

Qustions I have are:

Should I replace BOTH relays? Fuel Pump Relay & A/C Compressor Relay?

Should I be expecting a fuel pump failure in the NEAR future?

CadillacSTS2003 · #2 (**permalink**) 01-05-07, 11:29 AM

relays are cheap
replacem both to be safe
keep the known good one for an emergency

Gearheaad43 · #3 (**permalink**) 01-05-07, 11:32 AM

Quote:

Originally Posted by CadillacETC1997

relays are cheap
replacem both to be safe
keep the known good one for an emergency

Yes sir!!!

**Ranger** · #4 (**permalink**) 01-05-07, 12:39 PM

I have yet to replace a relay, so I would say if it ain't broke, don't fix it. Just replace the bad relay. No, I would not expect a pump failure in the near future. The problem was the relay, not the pump.

clarkz71 · #5 (**permalink**) 01-05-07, 02:19 PM

I don't know about Cadillac, but when a Mercedes blows a fuel pump relay, usually it's because the fuel pump is starting to go, and is drawing to many amps for the relay. Common problem on 80's and early 90's Benz.

**Ranger** · #6 (**permalink**) 01-05-07, 05:25 PM

Clark, wouldn't that take out a fuse before the relay? I'm not disargreeing with you. Just asking because I don't know for sure. Just seems logical to me.

clarkz71 · #7 (**permalink**) 01-05-07, 05:29 PM

Again, I havn't looked at the circuit in my FSM, but the relay is what carry's the load, it's not a short, just an increased load on the circuit. I would imagine a shorted pump or power supply wire would blow the fuse, in that case the car wouldn't start after switching relays.

clarkz71 · #8 (**permalink**) 01-05-07, 05:47 PM

OK, here's the circuit. As you can see there's a 20 amp fuse suppling the relay. When a relay used to fail in a Benz, I measured the pump draw at 15 amps. A good pump would only draw 6 or 7 amps. If this was the case with a caddy, a 20 amp fuse wouldn't blow, the relay however would. I might pull my relay this weekend and measure the amps a caddy pump pulls.