Fuel System Diagnosis (K07UFM)
Fuel System Diagnosis (LC8\K07\UFM)
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 engine control module (ECM) enables the fuel pump relay when the ignition switch is turned ON. The ECM will disable the fuel pump relay within 30 seconds unless the ECM detects ignition reference pulses. The ECM continues to enable the fuel pump relay as long as ignition reference pulses are detected. The LPG cut-off solenoid valve and fuel pump are active when the fuel pump relay is energized. When the ignition is initially ON the LPG control module turns on the wait to start lamp for 5-8 seconds. The LPG control module also enables the control circuit to the LPG bypass relay for 2-5 seconds if the fuel temperature and pressure are within the calibrated range that requires the system to be purged.
Reference Information
Description and Operation
Fuel System Description (LC8\K07\UFP) Description and OperationFuel System Description (LC8\FHZ) Description and OperationFuel System Description (LC8\K07\UFM) Description and OperationFuel System Description (Without LC8) Description and Operation
Electrical Schematics
Engine Controls Schematics [1][2]Electrical Diagrams
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
Special Tools
CH-50933 pressure gauge or equivalent
Circuit/System Verification
Note:
* Repair all fuel system related DTCs before performing this diagnostic, unless instructed here from a DTC diagnostic.
* Inspect the fuel system for damage or external leaks before proceeding.
* Verify that adequate fuel is in the fuel tanks before proceeding.
1. Ignition OFF, all vehicle systems OFF, install a 0-2069 kPa (0-300 psi) fuel pressure gauge at the fuel rail, refer to Fuel Pressure Gauge Installation and Removal Testing and Inspection. It may take up to 2 minutes for all vehicle systems to power down.
2. Record the pressure reading on the gauge.
3. Ignition ON.
4. Verify there is an audible click from the Q58 LPG cut-off solenoid valve and the G40 LPG fuel pump is ON for 30 seconds.
• If NO audible click from the LPG cut-off solenoid valve or the LPG fuel pump is OFF
Refer to the Circuit/System Testing
• If an audible click from the LPG cut-off solenoid valve and the LPG fuel pump is ON
5. Ignition OFF, all vehicle systems OFF. It may take up to 2 minutes for all vehicle systems to power down.
Note:
* The LPG control module must not receive a signal from the fuel pump relay for greater than 2 minutes before the purge cycle will be enabled. When the key is turned to the ON position the engine control module will enable the fuel pump relay for 30 seconds. The LPG control module may ground the control circuit of the LPG bypass relay for the first 2-5 seconds if the LPG temperature and pressure is within the calibrated range that requires the system to be purged. After 2-5 seconds the LPG control module disables the LPG bypass relay.
* Pressure differences may change slightly depending on altitude and ambient temperatures
* Verify all manual tank valves are open
6. Ignition ON.
7. Verify the fuel pressure increases 275- 414 kPa (40-60 psi).
• If the pressure does not increase 275- 414 kPa (40-60 psi)
Refer to the LPG Fuel Pump Testing
• If the pressure increased greater than 414 kPa (60 psi)
Verify the manual valves are OPEN, inspect for a kinked or restricted fuel return line. If no concern is present test or replace the Q71 LPG bypass solenoid assembly.
• If the pressure increased 275- 414 kPa (40-60 psi)
8. All OK
Circuit/System Testing
1. Ignition OFF.
2. Verify the LPG tank manual valves are OPEN
3. Disconnect the harness connector at the Q58 LPG cut-off solenoid valve
4. Test for 10 ohms or less between the Q58 LPG cut-off solenoid valve ground circuit terminal B and ground.
• If 10 ohms or greater
1. Ignition OFF
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
5. Connect a test lamp between the Q58 LPG cut-off solenoid valve voltage supply circuit terminal A and ground. Ignition ON.
6. Verify the test lamp illuminates when commanding the fuel pump ON and OFF with a scan tool.
• If the test lamp does not illuminate
Refer to Fuel Pump Electrical Circuit Diagnosis (FPCM) Fuel Pump Electrical Circuit DiagnosisFuel Pump Electrical Circuit Diagnosis (LC8\K07\UFP) Testing and InspectionFuel Pump Electrical Circuit Diagnosis (LC8\FHZ) Testing and InspectionFuel Pump Electrical Circuit Diagnosis (Without FPCM) Fuel Pump Electrical Circuit DiagnosisFuel Pump Electrical Circuit Diagnosis (LC8\K07\UFM) Testing and Inspection.
• If the test lamp illuminates
7. Connect the harness connector at the Q58 LPG cut-off solenoid valve. Ignition ON
8. Verify the Q58 LPG cut-off solenoid valve turns ON and OFF when commanding the Fuel Pump Relay ON and OFF with a scan tool.
• If the LPG cut-off solenoid valve does not turn ON and OFF
Test or replace the Q58 LPG cut-off solenoid valve.
• If the LPG cut-off solenoid valve turns ON and OFF
Refer to LPG Fuel Pump Testing
LPG Fuel Pump Testing
1. Ignition OFF.
2. Disconnect the fuel pump in-line harness connector at the LPG fuel tank pass through.
3. Test for 10 ohms or less between the G40 LPG fuel pump ground circuit terminal B and ground.
• If 10 ohms or greater
1. Ignition OFF
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
4. Connect a test lamp between the G40 LPG fuel pump voltage supply circuit terminal A and ground. Ignition ON.
5. Verify the test lamp illuminates when commanding the fuel pump ON and OFF with a scan tool.
• If the test lamp does not illuminate
Refer to Fuel Pump Electrical Circuit Diagnosis (FPCM) Fuel Pump Electrical Circuit DiagnosisFuel Pump Electrical Circuit Diagnosis (LC8\K07\UFP) Testing and InspectionFuel Pump Electrical Circuit Diagnosis (LC8\FHZ) Testing and InspectionFuel Pump Electrical Circuit Diagnosis (Without FPCM) Fuel Pump Electrical Circuit DiagnosisFuel Pump Electrical Circuit Diagnosis (LC8\K07\UFM) Testing and Inspection.
• If the test lamp illuminates
6. Connect the harness connector at the G40 LPG fuel pump. Ignition ON
7. Verify the G40 LPG fuel pump turns ON and OFF when commanding the Fuel Pump Relay ON and OFF with a scan tool.
• If the LPG fuel pump does not turn ON and OFF
Test or replace the G40 LPG fuel pump.
• If the LPG fuel pump turns ON and OFF
8. Ignition OFF.
9. Disconnect harness connector at the Q71 LPG bypass solenoid. Ignition ON.
10. Verify the fuel pressure increases 275- 414 kPa (40-60 psi) when commanding the fuel pump relay ON with a scan tool.
• If the fuel pressure does not increase 275- 414 kPa (40-60 psi)
Test or replace the G40 LPG fuel pump.
• If the fuel pressure increases 275- 414 kPa (40-60 psi)
Refer to LPG Bypass Solenoid Testing
LPG Bypass Solenoid Testing
1. Ignition OFF, disconnect the LPG bypass relay.
2. Verify a test lamp illuminates between the B+ circuit terminal 86 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance,
3. Test for greater than 15 ohms between the component control circuit terminal 87 and ground.
• If less than 15 ohms, repair the short to ground on the circuit.
• If greater than 15 ohms, test or replace the LPG bypass relay.
• If the test lamp illuminates
3. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
• If the test lamp does not illuminate
1. Ignition OFF.
2. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If the test lamp illuminates
4. Connect a test lamp between the B+ circuit terminal 86 and the component control circuit terminal 85.
5. Verify the test lamp does not illuminate.
• If the test lamp illuminates
1. Ignition OFF, disconnect the harness connector at the LPG control module.
2. Test for infinite resistance between the component control circuit terminal 22 and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the LPG control module.
• If the test lamp does not illuminate
6. Disconnect the harness connector at the LPG control module.
7. Connect a 3 A fused jumper between the component control circuit terminal 22 and ground.
8. Verify the test lamp illuminates.
• If the test lamp does not illuminate
1. Remove the test lamp.
2. Test for less than 1 V between the component control circuit and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, repair the open/high resistance in the circuit.
• If the test lamp illuminates
9. Disconnect the harness connector at the Q71 LPG bypass solenoid.
10. Test for less than 10 ohms between the Q71 LPG bypass solenoid ground circuit terminal B and ground.
• If 10 ohms or greater
1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.
• If less than 10 ohms
11. Connect the harness connector at the Q71 LPG bypass solenoid.
12. Connect a 20 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
13. Verify the Q71 LPG bypass solenoid is activated.
• If the LPG bypass solenoid does not activate
1. Test for less than 2 ohms in the control circuit terminal 87 end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, test or replace the LPG bypass solenoid.
• If the LPG bypass solenoid activates
14. Test or replace the LPG bypass relay.
Component Testing
Relay Test
1. Ignition OFF, disconnect the LPG bypass relay.
2. Test for 70-110 ohms between terminals 85 and 86.
• If less than 70 ohms or greater than 110 ohms
Replace the relay.
• If between 70-110 ohms
3. Test for infinite resistance between the terminals listed below:
* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87
• If less than infinite resistance
Replace the relay.
• If infinite resistance
4. Install a 20 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground.
5. Test for less than 2 ohms between terminals 30 and 87.
• If 2 ohms or greater
Replace the relay.
• If less than 2 ohms
6. All OK
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
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