P2634 indicates the powertrain control module (PCM) has detected a higher-than-expected voltage on the control circuit for the secondary or 'B' fuel pump. This typically means the circuit is shorted to battery voltage, the fuel pump driver is inoperative, or there is an open in the low-side driver path causing a pulled-up voltage reading. The code sets when the monitored voltage remains above the calibrated threshold while the pump is commanded off or during self-tests.
The control circuit wiring is chafed, pinched, or damaged, creating a short to a 12-volt source elsewhere in the harness. This is the most common cause, often occurring where harnesses pass through bulkheads or near sharp edges.
The internal driver circuit of the fuel pump control module (if equipped) has failed, causing a constant high voltage feedback or an inability to properly ground the control circuit.
Internal shorting or open circuits within the fuel pump assembly itself are altering the control circuit voltage characteristics, or the pump's internal wiring is compromised.
Moisture intrusion, bent pins, or poor terminal tension in the connectors at the pump, control module, or PCM are causing high resistance or voltage bleed-over on the control line.
Rarely, the internal low-side driver within the PCM is damaged or shorted to voltage internally; this should only be considered after all external wiring and components are verified good.
You should not drive the vehicle; a fault in the fuel pump control circuit can cause sudden fuel starvation and engine stalling, creating a safety hazard.
Not necessarily; while the pump could be at fault, wiring shorts and control module failures are statistically more common causes that should be ruled out first through circuit testing.
No; PCM failure causing this specific code is rare. The vast majority of P2634 faults are resolved by repairing wiring shorts or replacing the fuel pump control module or pump assembly itself.
The 'B' designation typically refers to a secondary fuel pump, a specific stage of a dual-pump system, or the control circuit monitored by a dedicated driver channel within the PCM or separate control module.