P0656

DTC P0656

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptors
P0656
- Fuel Level Output Circuit

Circuit Description

The fuel level sensor changes resistance based on fuel level. The fuel level sensor has a ignition circuit, signal circuit and a low reference circuit. The ECM monitors the signal circuit for changes in voltage caused by changes in the resistance of the sensor in order to determine fuel level.

When the fuel tank is full, the sensor resistance is low, and the ECM signal voltage is high. When the fuel tank is empty, the sensor resistance is high, and the signal voltage is low.

The ECM uses inputs from the fuel level sensor in order to calculate the total fuel percentage remaining in the fuel tank. The ECM uses the fuel level information for the evaporative emission (EVAP) and misfire diagnostics. The fuel level information is sent to the instrument panel cluster (IPC).

If the ECM detects a signal voltage lower than the operating range of the sensor, this DTC sets.

Conditions for Running the DTC

* The engine is running.
* DTC P0656 runs continuously once the above conditions are met.

Conditions for Setting the DTC

* The ECM detects that fuel level signal voltage is less than 0.25 volt.
* The above condition is present for more than 10 seconds.

Action Taken When the DTC Sets

* The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
* The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.
* The fuel gauge defaults to empty.

Conditions for Clearing the MIL/DTC

* The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
* A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
* A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

Reference Information
Schematic Reference

Instrument Cluster Schematics (without WHB) (Instrument Cluster Schematics (without WHB))Instrument Cluster Schematics (with WHB) (Instrument Cluster Schematics (with WHB))
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Instrument Panel Description (Description and Operation)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the fuel pump and sender assembly.
2. Ignition OFF for 60 seconds, doors closed, test for less than 5 ohms between the low reference circuit terminal 6 and ground.

• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for B+ between the ignition circuit terminal 4 and ground

• If not the specified value, test the ignition circuit for a short to ground or an open/high resistance.

4. Verify the scan tool Fuel Level Percentage parameter is less than 5%.

• If greater than the specified range, test the signal circuit terminal 1 for a short to voltage. If the circuit tests normal, replace the ECM.

5. Install a 3-amp fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 6. Verify the scan tool Fuel Level Percentage parameter is greater than 95%.

• If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal replace the ECM.

6. If all circuits test normal, test or replace the fuel pump and sender assembly.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Fuel Sender Assembly Replacement (Service and Repair) for the 1.4L (LDT) engine
* Fuel Sender Assembly Replacement (Service and Repair) for the 1.6L (LXT) engine
* Fuel Sender Assembly Replacement (Service and Repair) for the 1.6L (LXV) engine
* Control Module References (Programming and Relearning) for the ECM replacement, setup, and programming.