What does it mean?
The voltage the module measures on the fuel pump module B control circuit has stayed lower than the level it expects for the state it commanded. On a circuit driven by a smart output the module watches the line to confirm it goes high when the driver is off and drops only when the driver switches; a line that is held down at all times means something is pulling it to ground. This is a genuine electrical fault, not a delivery performance issue, and it can occur with the pump running, not running, or with the ignition simply switched on. Because the module protects its own output stage, it usually disables the circuit once the low condition repeats. That can leave the second pump inactive with the fuel supply problems that follow from it.
Symptoms
- MIL on, frequently with a blown fuse in that circuit
- Second pump not operating, which can cause long cranking or a no-start
- Fuel starvation and power loss at high demand or when the tank is low
- Stalling on cornering in vehicles that rely on a transfer pump
- Fuel gauge reading incorrectly on saddle tank systems where transfer has stopped
- Sometimes no driveability complaint at all until the tank level drops
Likely causes
- Control wire shorted to ground, often where the harness passes over a body seam or a fuel line bracket
- Internally shorted pump motor or driver in the pump module pulling the circuit down
- Water or road salt inside the tank flange connector creating a low resistance path to ground
- Chafed or crushed wiring under the rear seat or along the underbody
- Damaged harness after a fuel pump, tank or exhaust repair
- Corroded terminal that has bridged to the connector shell
- Failed output driver inside the control module, considered only after the harness and pump test good
How to fix it
- Check the fuse for that circuit and note whether it has failed, which already narrows the search to a short
- Disconnect the pump module and see whether the low voltage condition disappears; if it does, the pump is the load pulling the line down
- With the pump unplugged, measure the control wire to ground for a short along its whole length
- Inspect the connector at the tank flange for water, corrosion and terminals touching the shell
- Follow the harness under the rear seat and along the underbody looking for chafe points and crush damage
- Repair or replace the damaged section of harness, or renew the pump module when it is proven to be internally shorted
- Clear the code, command the pump and confirm the circuit voltage now follows the commanded state