What does it mean?
This diagnostic code (DTC) is a generic powertrain code, meaning it applies to vehicles equipped with OBD-II. Although generic, specific repair steps may vary by make/model.
The fuel pump is powered by the fuel pump relay. When the PCM (Powertrain Control Module) activates the fuel pump relay, voltage is supplied to the fuel pump and it pressurizes the fuel system. Some vehicles have a feedback on the fuel pump voltage supply circuit. This is simply a circuit spliced into the fuel pump voltage supply. The splice is typically located near the PCM.
The PCM monitors this feedback circuit to ensure the correct voltage is being sent to the fuel pump. By activating the fuel pump relay, it expects to see battery voltage on the feedback circuit. If the PCM detects an unexpected intermittent problem with the signal when the fuel pump is not activated, P0233 may set.
Symptoms
Symptoms of a P0233 DTC may include:
MIL (Malfunction Indicator Lamp) illumination
Fuel pump runs without the key
Small amount of voltage present on the FP (Fuel Pump) voltage supply circuit due to a short circuit
Causes
Potential causes of a P0233 code include:
Faulty FP relay
Short to voltage on the FP voltage supply circuit or the feedback circuit
Short to ground at the PCM
PCM FP relay control circuit
FP relay control driver shorted to ground internally
Possible Solutions
With a P0233, it is possible for the fuel pump to run continuously, even with the ignition off. If this is the case and you can hear the fuel pump running, you may be able to skip some of the following checks. Turn the key to KOEO (Key On Engine Off) and wait a few seconds. This allows the PCM to complete its fuel pump pre-cycle. Now, using your scan tool (if you have one), observe the FP VOLTAGE FEEDBACK reading in the data stream. This reading indicates the type of voltage the fuel pump is receiving.
If you do not have access to a scan tool, use a voltmeter to read the FP voltage at the fuel tank. If your reading indicates any voltage present at the fuel pump with KOEO (or if you can hear the pump running), remove the FP relay. If the voltage remains or the fuel pump continues to run, there is a short to voltage on the FP voltage supply circuit or the feedback circuit. Repair as necessary. If the voltage goes away (or the pump stops running) with the FP relay removed, try replacing the relay with a spare relay. When reinstalling the spare relay, if the voltage goes away, the relay was faulty due to a short. If, however, after replacement the relay voltage is still present, suspect that the PCM FP relay control circuit is shorted to ground.
Check for a short to ground on the PCM FP relay control circuit (ground driver) by removing the FP relay and ohming between a good ground and the PCM FP relay control. There should be no continuity to ground with KOEO (once the FP pre-cycle is complete). If there is continuity to ground, the wire is shorted. Locate the short to ground and repair as necessary. If you find no physical short, it may be necessary to cut the FP relay control wire near the PCM connector where it will be easy to repair and check for continuity to ground with KOEO coming from the PCM. If there is no continuity, the wire is shorted in the harness. But if there is continuity, the driver may be shorted internally and the PCM may require replacement.