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.  
MIL comes on and stays on, or never comes on at all, no DTCs set Troubleshoot the MIL circuit.  
Engine will not start
(MIL works OK, no DTCs set, immobilizer indicator stays on or flashes) 		Check for symptoms for the immobilizer system.  
Engine starts but stalls immediately
(MIL works OK, no DTCs set, immobilizer indicator stays on or flashes) 		Check for symptoms for the immobilizer system.  
Hard starting
(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. 		Do the ECM/PCM idle learn procedure.
Check the idle speed. 		 
Cold fast idle too high
(MIL works OK, no DTCs set) 		1.

2.
3. 		Do the ECM/PCM idle learn procedure.
Check the idle speed.
Test the throttle body. 		 
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. 		Troubleshoot the alternator FR signal circuit.
Inspect the APP sensor. 		 
After warming up, idle speed drops when steering wheel is turning
(MIL works OK, no DTCs set) 		1.

2. 		Do the ECM/PCM idle learn procedure.
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.
6.
7. 		Do the ECM/PCM idle learn procedure.
Test the fuel pressure.
Except KQ model:
Test the injectors.
Troubleshoot the alternator FR signal circuit.
Inspect the PCV valve.
Test the throttle body.
Except KQ model:
Troubleshoot the VTEC system oil pressure. 		Contaminated fuel 
Misfire or rough running
(MIL works OK, no DTCs set)
- Except KQ 		1.
2.
3.
4.
5. 		Check the spark plugs.
Test the fuel pressure.
Test the injectors.
Troubleshoot the fuel pump circuit.
Except KQ model:
Troubleshoot the VTEC system oil pressure. 
  • Low compression
  • Valve clearance
  • Contaminated fuel
 
Fails emission test
(MIL works OK, no DTCs set)
- Except KQ 		1.

2.
3.
4.
5.
6. 		Inspect the three way catalytic converter (TWC).
Check the spark plugs.
Test the fuel pressure.
Test the injectors.
Check the EVAP system.
Except KQ model:
Troubleshoot the VTEC system oil pressure. 
  • Contaminated fuel
  • Low compression
  • Slipped/ broken timing belt
 
Low power
(MIL works OK, no DTCs set) 		1.
2.
3.
4.


5.

6. 		Test the fuel pressure.
Check the air cleaner element.
Test the throttle body.
Except KQ model:
Inspect the three way catalytic converter (TWC).
Except KQ model:
Test the injectors.
Except KQ model:
Troubleshoot the VTEC system oil pressure. 
  • Contaminated fuel
  • Low compression
  • Camshaft timing
  • Engine oil level
 
Engine stalls
(MIL works OK, no DTCs set) 		1.

2.
3.
4.

5.

6. 		Do the ECM/PCM idle learn procedure.
Test the fuel pressure.
Check the idle speed.
Troubleshoot the brake pedal position switch signal circuit.
Except KQ model:
Check the spark plugs.
Except KQ model:
Troubleshoot the VTEC system oil pressure. 
  • Intake air leaks
  • Faulty harness and sensor connections
 
HDS does not communicate with the ECM/PCM or the vehicle Troubleshoot the DLC circuit.