Second Fuel Pump Malfunction (Ford)
What does P1243 mean?
The P1243 code means the vehicle's onboard diagnostic system has detected: Second Fuel Pump Malfunction (Ford). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Loss of power at high engine loads
- Engine stumble during towing
- Fuel pressure drops under sustained load
- Bogs down at highway speeds
Probable Causes (Ranked by Likelihood)
- Secondary fuel pump failure Very High
- Secondary fuel pump relay failure High
- Wiring fault to secondary fuel pump Moderate
- Clogged secondary fuel pump inlet strainer Moderate
- PCM secondary pump control circuit failure Low
Step-by-Step Diagnostic Procedure
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Verify secondary pump activates under high load with scan tool
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Check secondary pump relay by swapping with known good relay
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Measure voltage at secondary pump connector during activation
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Inspect wiring and connectors to the secondary fuel pump
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Monitor fuel pressure under sustained high-load conditions
Frequently Asked Questions
What vehicles have a second fuel pump?
Ford diesel and some heavy-duty gas trucks use a secondary fuel pump for high-load conditions such as towing. This is common on Super Duty trucks and E-series vans.
Why does P1243 only appear when towing?
The secondary pump activates only under high fuel demand. At normal loads, the primary pump is sufficient. The fault becomes apparent only when the secondary pump is needed.
Can I drive without the secondary fuel pump working?
You can drive at moderate speeds, but towing or sustained high-speed driving may cause fuel starvation and power loss. Avoid heavy loads until repaired.