P0628 indicates the powertrain control module (PCM) has detected a voltage level below the expected threshold in the fuel pump control circuit. This circuit commands the fuel pump control module (FPCM) or a driver/relay that supplies power to the fuel pump motor. A low signal typically points to an open circuit, a short to ground, or a driver failure inside the FPCM.
The FPCM's internal driver transistor can fail open or shorted to ground, pulling the control circuit low. This is the most common root cause on vehicles that use a separate FPCM.
Damaged, corroded, or disconnected wiring between the PCM and FPCM (or between the PCM and fuel pump relay/driver) will cause the PCM to see a low voltage on the command circuit.
A worn or seized fuel pump motor can pull enough current to drag the control circuit voltage low, especially if the FPCM uses a low-side driver with current monitoring.
On systems that use a PCM-driven relay, a stuck-open relay coil or a shorted driver inside the PCM can set this code, though the PCM driver itself is a less frequent failure point.
An internal PCM driver fault is possible but rare; it should only be considered after the FPCM, wiring, and pump motor have been ruled out.
No. The PCM driver is a rare failure point. The fuel pump control module (FPCM), its wiring, or the fuel pump motor itself are far more likely causes.
Yes. If the pump motor draws excessive current, it can pull the control circuit voltage low, especially on systems where the FPCM monitors current on the low-side driver.
Not necessarily. The pump may run intermittently, run at reduced speed, or not run at all depending on the nature of the circuit fault.
No. Replace only the component that testing confirms is faulty. Unnecessary PCM replacement is a common and costly misdiagnosis for this code.