Technical Description of OBD-II Trouble Code
Malfunction in the Fuel Level Output Circuit
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Saturn, Ford, GMC, Mercedes Benz, Holden, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P0656 indicates that the powertrain control module (PCM), or one of the other related controllers, has detected an inconsistency in the fuel level output circuit.
The fuel level gauge is an essential component of the instrument panel. It allows the driver to monitor the vehicle’s fuel level while operating it. Typically, the PCM receives a signal from the fuel level sensor located in the fuel storage tank. This signal enables the PCM to calculate fuel mileage, monitor fuel tank pressure, and fuel temperature. This data is used to determine the engine’s fuel delivery strategy, and then the fuel level output signal is sent to the fuel gauge and/or instrument panel controller. It may also be sent to the low fuel lamp and other on-board controllers.
If a problem is detected in monitoring the fuel level output circuit, a code P0656 will be stored and a malfunction indicator lamp (MIL) may illuminate.
Typical simple gauges:
What is the severity of this DTC?
A P0656 should be considered moderate because it could result in an inoperative fuel gauge and/or drivability issues, and there is a possibility of running out of gas.
What are some of the symptoms of the code?
Symptoms of a P0656 trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P0656 troubleshooting steps?
Refer to your vehicle information source for technical service bulletins (TSB) that match the stored code, vehicle details (year, make, model, and engine), and exhibited symptoms. If you find the relevant TSB, it may provide helpful diagnostic information.
To accurately diagnose a code P0656, you will need a diagnostic scanner and a digital volt/ohmmeter. You will also require a reliable source of vehicle information.
Start by connecting the scanner to the vehicle’s diagnostic port and retrieving all stored codes and freeze frame data. It is advisable to write down this information in case the code is intermittent.
After recording all relevant information, clear the codes and test drive the vehicle (if possible) until the code is reset or the PCM enters readiness mode.
If the PCM enters readiness mode, the code is intermittent and will be even more challenging to diagnose. The condition that caused the P0656 to be stored may need to worsen before an accurate diagnosis can be made. On the other hand, if the code fails to reset and there are no drivability symptoms, the vehicle can be operated normally.
If the P0656 code is immediately reset, proceed with a visual inspection of the system’s wiring and connectors. Repair or replace any broken or unplugged harnesses as necessary.
If the wiring and connectors appear to be functional, obtain the appropriate wiring diagrams, connector face views, connector pin-out charts, and diagnostic flow charts from your vehicle information source.
Once you have the correct information, use your DVOM to test the fuel level output circuit at the appropriate pin of the PCM connector. If no fuel level output signal is detected, suspect that the PCM is defective or there is a PCM programming error.
If a fuel level output signal is detected at the PCM connector, test the corresponding circuit (as presented) at the fuel level gauge pin of the instrument panel connector. If the fuel level output signal is not detected, there is an open circuit between the PCM and the fuel gauge in the instrument panel. Repair or replace the circuit and retest.
