Still Wondering how to fix DTC # 543


New Member
May 19, 2005
I have a '95 GT and have been experiencing a really bad running car at partial throttle. It misses and somtimes pops. DTC shows # 543 which = Fuel pump monitor shows no power / Secondary fuel pump circuit open to PCM, or somthing like that. I have an adjustable fuel pressure regulator and I have to run it around 50 psi to get it to run smoother. Runs fine at wide open throttle, but around town It drives me crazy with the chugging. How do I fix this?? Thanks for any help
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seems to me that you have an electronic issue (CCRM, etc) rather than the pump itself. Bump for ya.

good luck.
Okay, I got a test light out and pulled out the harness on the Constant Control Relay Module. I put the light on the DK GRN/ YEL Wire from the fuel pump inertia switch, turned the ignition on, and no light came on. I guess the fuel pump is just running off of battery juice and not getting messages from the CCRM.??
The CCRM is what supplies power to the pump (it is the relay) - that code might indicate an intermittant issue (or indicate that at some point you lost power to the pump).

The 94-95 section guys might be able to shed some more light into the issue (V8 foxes dont have CCRM's).

good luck.