Fuel Pump Secondary Circuit Low (Ford)
What does P1231 mean?
The P1231 code means the vehicle's onboard diagnostic system has detected: Fuel Pump Secondary Circuit Low (Ford). This is a critical severity code.
Common Symptoms
- Check Engine Light on
- Engine stalling during driving
- No start condition
- Engine sputtering under load
- Loss of power at higher RPMs
Probable Causes (Ranked by Likelihood)
- Fuel pump driver module (FPDM) failure Very High
- Poor ground at FPDM mounting point High
- Corroded wiring between FPDM and fuel pump Moderate
- Failing fuel pump motor Moderate
- Fuel pump relay failure Low
Step-by-Step Diagnostic Procedure
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Check the FPDM output voltage to the fuel pump (should vary with demand)
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Inspect the FPDM ground connection for corrosion or looseness
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Test fuel pump current draw (high current indicates a failing pump)
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Check wiring between the FPDM and fuel pump for resistance
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Replace the FPDM if output is below specification
Frequently Asked Questions
What is the fuel pump secondary circuit?
The secondary circuit is the output side of the fuel pump driver module -- the wiring that goes from the FPDM to the fuel pump itself. P1231 indicates this circuit has low voltage, meaning the pump is not receiving enough power.
Why does the FPDM fail?
The FPDM on Ford vehicles is mounted in an exposed location and is prone to water and mud exposure. Corrosion at the connector and ground point is the most common failure mode. Heat cycling also contributes to failure.
Can I test the fuel pump separately?
Yes. You can bypass the FPDM temporarily by connecting the fuel pump directly to 12V. If the pump runs normally, the FPDM is likely the problem. Do not leave it bypassed permanently as it eliminates pressure control.