P027B - Fuel Pump Module B Control Circuit High
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
Step-up or Fuel Pump Module B Control Circuit High indicates that the PCM (Powertrain Control Module) has detected a voltage signal that is higher than the expected range on the fuel pump control circuit. This is typically caused by a short to voltage in the wiring harness or a failure within the fuel pump driver module (FPDM). The circuit often utilizes Pulse Width Modulation (PWM) to control pump speed; a 'high' condition means the feedback or command signal is stuck at source voltage, preventing precise pressure regulation and potentially triggering a limp-home mode to protect the high-pressure fuel system.
Possible Causes
Short to voltage in the fuel pump module B control circuit wiring
Faulty Fuel Pump Driver Module (FPDM)
Corroded connectors causing voltage leakage or poor ground reference
Internal failure in the Powertrain Control Module (PCM)
Symptoms
Recommended Solution
- Visual Inspection: Check wiring and connectors to the fuel pump module for chafing, melted insulation, or corrosion.
- Voltage Measurement: Test the control circuit with the ignition on. With the module disconnected, the signal pin should typically show 0V or a low reference voltage. If 12V is present without command, there is a short to voltage.
- Scanner Diagnosis: Perform a fuel pump actuation test and monitor the PWM Duty-cycle. If signal stays at 100% regardless of command, diagnose the module or ECU output.
- Ground Check: Verify the module ground point has resistance below 0.5 Ohms.
- Replacement: Replace Fuel Pump Module B or repair wiring as identified during testing.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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