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Fuel and Emissions Systems Symptom Troubleshooting Index

When the vehicle has one of these symptoms, check for a diagnostic trouble code (DTC) with the HDS. 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.
4.
  • Low compression
  • No ignition spark
  • Intake vacuum leaks
  • Locked up engine
  • Broken cam chain
  • Fuel contamination
Engine will not start (MIL comes on and stays on, no DTCs set)
  • Low compression
  • No ignition spark
  • Intake vacuum leaks
  • Locked up engine
  • Broken cam chain
  • Fuel contamination
  • No power to ECM/PCM
  • No ground to ECM/PCM
  • Shorted reference voltage
MIL comes on and stays on, or never comes on at all, no DTCs set
Engine will not start (MIL works OK, no DTCs set, immobilizer indicator stays on or flashes)
Engine starts but stalls immediately (MIL works OK, no DTCs set, immobilizer indicator stays on or flashes)
Engine is hard starting (MIL works OK, no DTCs set)
1.
2.
3.
  • Low compression
  • Intake air leaks
  • Fuel contamination
  • Weak spark
Cold fast idle too low (MIL works OK, no DTCs set)
1.
2.
3.
Incorrect valve adjustment
Cold fast idle too high (MIL works OK, no DTCs set)
1.
2.
3.
Incorrect valve adjustment
After warming up, idle speed is below specifications without load (MIL works OK, no DTCs set)
1.
2.
  • Intake vacuum leaks
  • Incorrect valve adjustment
After warming up, idle speed is above specifications without load (MIL works OK, no DTCs set)
1.
2.
Intake vacuum leaks
Idle speed fluctuates (MIL works OK, no DTCs set)
1.
2.
3.
4.
5.
6.
7.
8.
Except KQ model: Test the injectors.
  • Fuel contamination
  • Intake vacuum leaks
Misfire or rough running (MIL works OK, no DTCs set)
1.
2.
3.
4.
5.
  • Low compression
  • Valve clearance
  • Fuel contamination
Fails emission test (MIL works OK, no DTCs set)
1.
2.
3.
4.
5.
6.
Except KQ model: Check the spark plugs.
Except KQ model: Test the injectors.
  • Fuel contamination
  • Low compression
  • Broken cam chain
Low power (MIL works OK, no DTCs set)
1.
2.
3.
4.
5.
6.
  • Fuel contamination
  • Low compression
  • Camshaft timing
  • Engine oil level
Engine stalls (MIL works OK, no DTCs set)
1.
2.
3.
4.
5.
6.
Except KQ model: Check the spark plugs.
  • Intake vacuum leaks
  • Faulty harness and sensor connections
  • Fuel contamination
Difficult to refuel
HDS does not communicate with the ECM/PCM or the vehicle