Fuel and Emissions Systems Symptom Troubleshooting

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. 
Test the battery.
Test the starter.
Check the fuel pressure.
Troubleshoot the fuel pump circuit. 
  • Low compression
  • No ignition spark
  • Intake air leaks
  • Locked up engine
  • Broken cam 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 stays on or flashes) 
Troubleshoot the immobilizer system.  
Engine is hard to start
(MIL works OK, no DTCs set) 
1.

2.
3. 
Test the battery.
Check the fuel pressure.
Test the throttle body. 
  • Low compression
  • Intake air leaks
  • Contaminated fuel
  • Weak spark
 
Cold fast idle too low
(MIL works OK, no DTCs set) 
1.

2.
3. 
Do the ECM/PCM idle learn procedure.
Check the idle speed.
Clean the throttle body. 
 
Cold fast idle too high
(MIL works OK, no DTCs set) 
1.

2.
3.
4. 
Do the ECM/PCM idle learn procedure.
Check the idle speed.
Inspect/adjust the throttle cable.
Do the throttle position learning check. 
 
Idle speed fluctuates
(MIL works OK, no DTCs set) 
1.

2.
3.
4. 
Do the ECM/PCM idle learn procedure.
Check the idle speed.
Inspect/adjust the throttle cable.
Do the carbon accumulation check. 
Intake vacuum leaks 
After warming up, idle speed is below specifications without load
(MIL works OK, no DTCs set) 
1.

2. 
Troubleshoot the alternator FR signal circuit.
Test the throttle body. 
 
After warming up, idle speed is above specifications without load
(MIL works OK, no DTCs set) 
1.
2. 
Inspect/adjust the throttle cable.
Troubleshoot the alternator FR signal circuit. 
 
After warming up, idle speed drops when steering wheel is turning
(MIL works OK, no DTCs set) 
1.

2.

3. 
Do the ECM/PCM idle learn procedure.
Troubleshoot the PSP switch signal circuit.
Test the throttle body. 
Power steering system 

Symptom Diagnostic procedure Also check for 
Idle speed fluctuates
(MIL works OK, no DTCs set) 
1.

2.
3.

4.
5. 
Do the ECM/PCM idle learn procedure.
Test the fuel pressure.
Troubleshoot the alternator FR signal circuit.
Inspect and test the PCV valve.
Test the throttle body. 
Contaminated fuel 
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.
Test the throttle body. 
  • Contaminated fuel
  • Low compression
  • Camshaft timing
  • Engine oil level
 
Engine stalls
(MIL works OK, no DTCs set) 
1.

2.
3.
4. 
Do the ECM/PCM idle learn procedure.
Test the fuel pressure.
Check the idle speed.
Troubleshoot the brake pedal position switch signal circuit. 
  • Intake air leaks
  • Faulty harness and sensor connections