Fuel pump secondary circuit fault CM code 543 | Ford Explorer Forums - Serious Explorations

  • Register Today It's free!

Fuel pump secondary circuit fault CM code 543


September 15, 2005
Reaction score
City, State
Greenville, SC
Year, Model & Trim Level
1993 Explorer XLT
I have a 1993 Ford Explorer that keeps blowing the EEC Fuse. The problem started in September and stopped. The problem started again two days ago.
I went through about 8 fuses and switched around circuit breakers today and was able to get my truck back home. I purchased a Ford code reader and Continuos Memory (CM) code 543 Fuel pump secondary circuit fault was retrieved. Where do I start in troubleshooting this fault. Thanks in advance.

CM 543 was the only code retrieved? No accompanying KOEO 543? Does the fuel pump run? How consistently does it pop the EEC fuse?

Depending on the answer to those questions, I would probably start by checking the wiring between the EEC relay and the fuel pump relay for any obvious shorts to ground. If I didn't see anything obvious, then verify other wiring coming off of the EEC relay for shorts. If I couldn't find anything obvious and it doesn't pop the fuse, then clear the CM code and see if it comes back.


Thanks again not only for your assistance to me, but to all others in this forum.
I was able to pull the following KOER CODES 116, 538, 536. The CM 543 code did not reappear. I might have left out something very important. I'm a ham operator and years ago I tried to do a mod to get rid of interference cause by the fuel pump. I had to spice the ground and power in the rear of vehicle leading to the fuel pump. When I removed the tape the power connection looked fine, but the black ground wire which still connected didn't look its best. Today I soldered both connections and re-taped them. Could this be a source of my problem. Right now the fuel pump works fine and the vehicle starts fine. It rained the day it happened and i have to travel thru different road conditiond delivering mail. Your question reference how often does it pop fuse. At the initial failure. It pops the fuse as soon as I turn the key and hear the fuel pump kick-in.

KOER 116 is often a result of running the KOER test without fully warming the engine up before the test. If you know you did get it warmed up, then it's possible the thermostat is partially stuck open or something else is preventing the computer from seeing what the engine temperature is. Did you perform the KOEO test? Did you get an KOEO 116 as well?

KOER 538 and 536 are almost always operator error during the test. 538 indicates that you neglected the "goose" test and 536 indicates that you neglected to press the brake after engine id was output. Review test instructions (and my "notes on pulling EEC-IV codes" in the EEC-IV forum if needed) and repeat test.

There's a lot of wire on these trucks, so I sometimes find it difficult to say with certainty, but I wouldn't expect your tinkering with the fuel pump wires near the tank to effect the EEC fuse. That wire/circuit is protected by the fuel pump fuse (right next the EEC fuse, isn't it).

There are a lot of different components that get power through the EEC fuse. I would suggest getting a wiring diagram so the next time it starts popping, you can try to start eliminating components.