Engine code 121 & 542 | Ford Explorer Forums - Serious Explorations

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Engine code 121 & 542


Active Member
August 14, 2015
Reaction score
Everett , wa
City, State
Everett washington
Year, Model & Trim Level
1992 , eddie bauer
Taco Run
So I hooked up my engr code reader and got some new ones

Code 121 o ( closed throttle voltage higher or lower than expected )

*how do I solve this problem ???

Code 542 c ( fuel pump secondary circuit fault )

** how do I solve this issue ???

Please help me this is my only car that I have for work .

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121: replace the TPS (Throttle Position Sensor) yellow circle in the pic.


542: Replace Fuel pump relay. Under the power distribution block. IIRC it's the brown one.


disconnect the battery before replacing any electrical components.

I have already replaced the throttle position sensor twice .. new one on it.

Check your battery, alternator ouput voltage and cables.

A low voltage situation can cause the reference voltage to be to low and cause false fault codes.

How do I test the alternator output voltage
And what cables do I check ? Battery cables?

Use a volt meter. 14.2 - 14 .7 with the engine running.

Battery should read no less than 12.6 with the engine off. Best to have the battery load tested at the Auto parts store.

Yes, battery cables.

I think you can have the alternator load tested at the parts store too.

Another possibility is a bad connection or short in the wiring somewhere.