Is your Caddy stalling out and not re-starting with a Service Fuel System Message? Getting a DTC PCM0231?.... It's a good chance your fuel pump relay contacts have loosened up. Follow these repair instructions:

Background: STS quit and I would get the "SERVICE FUEL SYSTEM" message on the DIC. With PCM0231 code. "Fuel pump relay low voltage". This happened once before and I had replaced the Fuel Pump Relay with a NEW OEM unit from GM. Worked fine for a couple months, then it started to quit again. Upon hooking up a fuel gauge, I was getting 48- 43 PSI with key on... no start.. It start up and run till I hit the FP relay with my hand/ or jiggled it a bit, car would stall and quit, fuel pressure reading drops to 0... I'd turn the Key off.. then back on and I still got 0...

If you are getting 43-45 psi on 1st key on....I doubt the fuel pump is the problem!! A bad pump will not show 45 PSI, plus if you had a fuel system leak, it would drop more than 5 PSI.....after a few minutes.

Please do this first before replacing that pump!!! I'd hate you see you fork over $170+ only to find out that was not the problem!!
From ewill3rd:The contact must be tight or the current won't flow.
That is a fairly high powered circuit, the current flowing through that connection over time can heat up the metal and cause it to relax making the connection loose. This might leave you with a good cold start but when the heat builds up it will loosen like a bi-metal strip.

I usually use a male connector as shown in the second photo to check the "tension" of the female. If you can get a male terminal and check each female you'll "feel" the one that is not tight enough.
Compare the "drag" as you pull the male terminal back out. If you find one that is loose, that is the one you need to replace or repair.

I hope this makes sense. The fuel pump circuits are the worst place for this due to the high current used and the terminals are just slightly too small to handle it over a really really long time.

Here is what I had to do: (Seville SLS STS Version)

* Disconnect battery
* Locate the Fuel Pump Relay (Forward (engine) compartment, drivers side junction block).
* Remove the electrical center cover
* Disengage the sub-terminal block containing the fuel pump/AC relay from the main block. (disengage 4 clips at bottom - pull up)
* Remove the FP relay.
* Remove the blue terminal locking clip on the side of the sub block.
* Using a Terminal release tool, Release the female FP relay terminal pins from the sub block.(Release/repair & re-install one at a time to prevent mis-locating pins)
* Bend the clips in the pins toward the opposite side to decrease the gap. (Release/repair & re-install one at a time to prevent mis-locating pins)
* Re-insert terminal pins into the sub-block. (Release/repair & re-install one at a time to prevent mis-locating pins)
* reinstall blue locking clip.
* Reinstall sub block assy. to the main block.
* Using mini-pliers, very slightly twist each one of the male pins on the FP relay.
* Re-install relay. Re-connect Battery.
* Turn key to run, check for fuel pressure.
* Start car.
* Re-install electrical center cover.
* Enjoy the Cadillac!!!


In addition to the above, using a test light I checked for power at the heavy pink wire at key turn on to ensure power delivery before starting the above repair.


Most likely you can not see a loose contact(s).. I strongly urge you to hit/ jiggle the FP relay the next time you get it started... If it quits or the Fuel pressure drops, I'm willing to bet it's the FP relay contacts