Fuel and Emissions Systems Symptom Troubleshooting (With ETCS)

Fuel and Emissions Systems Symptom Troubleshooting

When the vehicle has one of these symptoms, check the diagnostic trouble code (DTC) with the scan tool. If there is no DTC, do the diagnostic procedure for the symptom, in the sequence listed, until you find the cause.

Symptom	Diagnostic procedure		Also check for
Engine will not start (MIL works OK, no DTCs set)	1. 2. 3.	Test the battery. Test the starter. Troubleshoot the fuel pump circuit.	Low compression No ignition spark Intake air leaks Locked up engine Broken timing chain Contaminated fuel
Engine will not start (MIL comes on and stays on, or never comes on at all, no DTCs set)	Troubleshoot the MIL circuit.
Engine will not start (immobilizer indicator light stays on or flashes)	Troubleshoot the immobilizer system.
Hard starting (MIL works OK, no DTCs set)	1. 2.	Test the battery. Check the fuel pressure.	Low compression Intake air leaks Contaminated fuel
Cold fast idle too low (MIL works OK, no DTCs set)	1. 2.	Do the ETCS learn procedure. Check the idle speed.
Cold fast idle too high (MIL works OK, no DTCs set)	1. 2. 3.	Do the ETCS learn procedure. Check the idle speed. Inspect/adjust the throttle cable.
Idle speed fluctuates (MIL works OK, no DTCs set)	1. 2. 3.	Do the ETCS learn procedure. Check the idle speed. Inspect/adjust the throttle cable.	Intake air leaks
After warming up idle speed is below specifications without load (MIL works OK, no DTCs set)	1. 2.	Do the ETCS learn procedure. Troubleshoot the alternator FR signal circuit.	Vacuum hose clogged/cracked/poor connection
After warming up idle speed is above specifications without load (MIL works OK, no DTCs set)	1. 2.	Do the ETCS learn procedure. Troubleshoot the alternator FR signal circuit.
Idle speed fluctuates (MIL works OK, no DTCs set)	1. 2. 3. 4.	Do the ETCS learn procedure. Test the fuel pressure. Troubleshoot the alternator FR signal circuit. Inspect and test the PCV valve.	Contaminated fuel

Symptom	Diagnostic procedure		Also check for
Misfire or rough running (MIL works OK, no DTCs set)	1. 2.	Test the fuel pressure. Troubleshoot the fuel pump circuit.	Low compression Valve clearance Contaminated fuel
Fails emission test (MIL works OK, no DTCs set)	1. 2. 3.	Inspect the three way catalytic converter (TWC). Test the fuel pressure. Check the EVAP emission control system.	Contaminated fuel Low compression Broken timing chain
Low power (MIL works OK, no DTCs set)	1. 2. 3. 4.	Test the fuel pressure. Check the air cleaner element. Inspect/adjust the throttle cable. Inspect the three way catalytic converter (TWC).	Contaminated fuel Low compression Camshaft timing Engine oil level
Engine stalls (MIL works OK, no DTCs set)	1. 2. 3.	Do the ETCS learn procedure. Test the fuel pressure. Check the idle speed.	Intake air leaks Faulty harness and sensor connections
Difficult to refuel	Inspect the breather line and the suction line.