Diagnostic Aids

Enter this test only when all steps under QUICK TEST have been successfully completed and engine still does not start or if directed here from another test or chart. This test is only intended to diagnose:

• Heated Oxygen Sensor (HO2S).
• HO2S and VPWR circuits and connections.
• Compuvalve.
• Vacuum systems.

HO2S-11 and HO2S-21 circuits are monitored by compuvalve. Information is used by compuvalve for fuel trim calculations. HO2S PID should vary between 0-0.3 and 0.6-1.0 volt while engine is operating at 2000 RPM. Also, a change from rich to lean should occur more than 5 times during a period of 10 seconds at 2000 RPM. DTCs P0132, P0134, P0152, P0154, P0171, P0172, P0174 and P0175 are unique to alternative fuel system and are set if compuvalve receives a continuously high or low input (more than or less than 0.55 volt for more than 120 seconds), or no activity from HO2S. Possible causes for these faults are:

• HO2S circuits are open or shorted to ground.
• Faulty HO2S sensor.
• Consistently lean or rich fuel system
• Faulty compuvalve.
• Faulty harness circuits (HO2S or VPWR).
• Intake air leaks.
• Plugged injectors.
• Pressure regulator inoperative.
• Exhaust leaks.
• PCV system.
• Ignition system faults.
• Low compression.