The fuel tank on this vehicle is equipped with 2 fuel level sensors, one for each reservoir of the fuel tank. Fuel is transferred from the left side of the fuel tank to the right side of the fuel tank in order to make sure all of the usable fuel volume is available. The fuel pump supplies a small amount of pressurised fuel to the siphon jet pump through the fuel feed pipe. The pressurised fuel creates a venturi action inside the siphon jet pump. The venturi action causes the fuel to be drawn out of the left side of the fuel tank. Fuel is then transferred from the left side of fuel tank to the right side of fuel tank through the internal fuel transfer tube. This diagnostic tests for too large of a difference in the fuel level between the left and right side of the fuel tank. The DTC sets if the engine control module (ECM) determines that the right side fuel level is less than a predetermined amount of the left side fuel level.

The following table illustrates the difference between temperature, resistance and voltage:

DTCs P0656 and P2636 are type C DTCs.

DTCs P0656 and P2636 are type C DTCs.

Depending on the current fuel level it may be difficult to locate a malfunctioning fuel level sensor. The condition may only occur when the fuel level is full or near empty. The fuel level sensor unit may need to be removed for further diagnosis. A fuel level sensor that has an intermittent condition causes this DTC to set.

Schematic Reference

Engine Controls Schematics.

Connector End View Reference

Component Connector End Views.

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions.

Scan Tool Reference

Control Module References for scan tool information

Engine idling for 5 minutes, using a scan tool observe the DTC information. DTC P0656 or P2636 should not set.

1. Ignition OFF, disconnect the harness connector of the left side fuel level sensor.
2. Ignition ON, verify the scan tool Fuel Level Sensor-Left Tank voltage parameter is at 5.0 volts.

⇒	If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.

3. Install a 3-A fusible link wire between the signal circuit terminal and a known ground. Verify the scan tool Fuel Level Sensor-Left Tank voltage parameter is at 0.0 volts.

⇒	If greater than the specified range, test the signal circuit for a high resistance. if the circuit tests normal, replace the ECM.

4. Install a 3-A fusible link wire between the signal circuit terminal and the low reference circuit terminal. Verify the scan tool Fuel Level Sensor-Left Tank voltage parameter is at 0.0 volts.

⇒	If greater than the specified range, test the low reference circuit for a high resistance, if the circuit tests normal, replace the ECM.

5. Remove the fuel tank. Refer to Fuel Tank Replacement.
6. Remove the fuel tank primary and secondary modules and inspect for the following conditions;

•	A clogged secondary fuel strainer and pick up.

•	A clogged or restricted siphon jet pump.

•	Broken, clogged or restricted flex tubes, primary fuel tank module.

•	Broken, clogged, disconnected or restricted fuel transfer tube inside tank.

⇒	If you find any of the above conditions, repair as necessary.

⇒	If all circuits/connections test normal, test or replace the left/secondary fuel level sensor.

1. Ignition OFF, remove the left fuel level sender from the fuel tank. Refer to Secondary Fuel Tank Module Replacement.
2. Connect a DMM between the low reference terminal and the signal circuit terminal on the fuel level sender.
3. Verify the secondary fuel level sender resistance remains within 40-250 ohms and changes smoothly while moving the float arm from stop to stop.

⇒	If the resistance is outside the specified range or changes erratically while moving the float arm from stop to stop, replace the fuel level sender.

Perform the Diagnostic Repair Verification.