Fuel Gauge Inaccurate or Inoperative (with LC8 and FHZ)

Fuel Gauge Inaccurate or Inoperative (with LC8 and FHZ)

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.

Circuit/System Description

The alternative fuel tank pressure sensor is a 3-wire sensor comprising of the signal circuit, the low reference circuit and a 5 V reference circuit. The compressed natural gas control module (CNGCM) monitors the signal of the pressure sensor to determine the amount of pressure in the tank. The CNGCM uses this signal in order to calculate the percentage of remaining gas in the tank and converts it to a PWM signal sent to the ECM. The ECM sends the fuel level percentage via the serial data circuit to the instrument cluster in order to control the fuel gauge.

Reference Information

Schematic Reference

Instrument Cluster Schematics Instrument Cluster Schematics

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Description and Operation

Instrument Cluster Description and Operation Instrument Cluster

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 Control Module References for scan tool information

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the alternative fuel tank pressure sensor.

2. Ignition OFF and all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down. Test for less than 10ohms between the low reference circuit terminal 1 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 CNGCM.

3. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal 3 and ground.

• If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the CNGCM.

• If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the CNGCM.

4. Install a 3A fused jumper wire at the signal circuit terminal 2. Toggle the jumper wire between the low reference circuit terminal 1 and the 5V reference circuit terminal 3. Verify the fuel gauge toggles between full and empty.

• If the fuel gauge does not toggle between full and empty, test the signal circuit for a short to voltage, short to ground or an open/high resistance.

5. Ignition OFF, connect the harness connector at the alternative fuel tank pressure sensor and disconnect the X2 harness connector at the CNGCM.

6. Ignition ON, test for 4.0-6.0V between the signal circuit terminal B and ground.

• 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.

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

• If within specified range, replace the CNGCM.

7. If all circuits test normal, replace the alternative fuel tank pressure sensor.

8. If the fuel gauge is still malfunctioning, replace the IPC.

Repair Instructions

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

* Compressed Natural Gas Control Module Replacement Service and Repair

* Control Module References Control Module References for the ECM and IPC replacement, programming and setup