Technical Description of OBD-II Trouble Code
The voltage in the Fuel Pump Secondary (Feedback) Circuit is too low.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The fuel pump is powered by the fuel pump relay. When the powertrain control module (PCM) activates the fuel pump relay, it supplies voltage to the fuel pump, pressurizing the fuel system. Some vehicles have a feedback circuit on the fuel pump supply circuit. This circuit is spliced into the voltage feed to the fuel pump and is usually located near the PCM.
The PCM monitors this feedback circuit to ensure that the fuel pump is receiving the correct voltage. When it activates the fuel pump relay, it expects to see battery voltage on the feedback circuit. If the voltage is too low or there is no voltage at all, it may trigger the P0231 code.
Symptoms
Symptoms of a P0231 DTC may include:
Causes
Possible causes of a P0231 code include:
NOTE: If there are no drivability complaints and the P0231 code is stored, suspect an open in the feedback circuit between the splice and the PCM.
Possible Solutions
When diagnosing fuel pump circuits, it is important to have a good wiring diagram. Try to locate one before attempting a complex repair. If the vehicle starts and runs without any drivability complaints, suspect an open in the feedback circuit between the PCM and the splice into the fuel pump supply voltage circuit. Repair as necessary.
If the vehicle does not start or starts and dies due to low fuel pressure, check the fuel pump fuse. If it is blown, check for a short to ground on the fuel pump voltage supply circuit. To do this, remove the FP relay and check the resistance between the voltage supply circuit at the fuel pump connector and ground. If there is low resistance indicating a short to ground, unplug the fuel pump and check again. If the resistance is high or infinite after unplugging the fuel pump, replace the shorted fuel pump. If the resistance is still low after unplugging the fuel pump, repair the short in the FP voltage supply circuit.
If the resistance check shows that the fuel pump supply circuit is okay, re-check between the FP fuse and the FP relay. There must be a short somewhere. Check for wiring harness chafing in specific areas. Repair as necessary. If the fuel pump fuse is not blown and the vehicle does not start or starts and stalls due to low fuel pressure, remove the fuse and check for voltage present at the fuse. Then check if voltage is traveling from the fuse to the FP relay by re-installing the FP fuse and checking for battery voltage at the FP relay. If the FP fuse or the FP relay does not have voltage supplied to it, the fuel pump will not operate. Find the open in the circuit and repair as necessary. If both the FP fuse and the FP relay have sufficient voltage, remove the FP relay and install a fused jumper wire to complete the FP voltage supply circuit (usually by jumping terminals 30 & 87 in most relays – check a wiring diagram to be sure). If the fuel pump runs, replace the faulty FP relay and recheck. If the fuel pump does not run, check for voltage present (with jumper connected or by cycling the ignition key with FP relay installed) at the fuel pump connector at the fuel tank. If voltage is present, verify that the ground circuit is intact. If both are okay, replace the fuel pump. If voltage is not present at the fuel pump with the fused jumper wire installed, repair the open in the fuel pump voltage supply circuit.
