Inspection Procedure 17
Inspection procedure 17: Too high CO and HC concentration when idlingCOMMENT
- Abnormal air/fuel ratio is suspected.
TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Fuel pump system failed.
- Heated oxygen sensor failed.
- Ignition system failed.
- Poor compression.
- Improper operation of the PCV valve.
- Evaporative emission control system failed.
- ECM failed.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A
STEP 1. Using scan tool MB991958, read the diagnostic trouble code (DTC).
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Read the DTC.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is any DTC set?
YES : Refer to, Diagnostic Trouble Code Chart. Diagnostic Trouble Code Descriptions
NO : Go to Step 2.
STEP 2. Check the ignition timing.
Refer to On-vehicle Service - Ignition Timing Check. Testing and Inspection
Q: Is the ignition timing normal?
YES : Go to Step 3.
NO : Check for installed conditions of the timing chain. Then confirm that the malfunction symptom is eliminated.
STEP 3. Using scan tool MB991958, check data list.
1. Turn the ignition switch to the "ON" position
2. Check the following items in the data list. Refer to Data List Reference Table Datal List Reference Table.
a. Item 5: Intake Air Temperature Sensor
b. Item 6: Engine Coolant Temperature Sensor
c. Item AC: Heated Oxygen Sensor (front)
d. Item AD: Heated Oxygen Sensor (rear)
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Are they operating properly?
YES : Go to Step 4.
NO : Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 4. Check the fuel pressure.
Refer to Fuel Pressure Test Testing and Inspection.
Q: Is the fuel pressure normal?
YES : Go to Step 5.
NO : Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 5. Check the spark plugs.
Refer to On-vehicle Service - Spark Plug Check and Cleaning. Testing and Inspection
Q: Are there any abnormalities?
YES : Replace the spark plug. Then confirm that the malfunction symptom is eliminated.
NO : Go to Step 6.
STEP 6. Check the ignition coil.
Refer to On-vehicle Service - Ignition Coil Check. Ignition Coil Check
Q: Are there any abnormalities?
YES : Replace the ignition coil. Then confirm that the malfunction symptom is eliminated.
NO : Go to Step 7.
STEP 7. Check the compression pressure.
Refer to On-vehicle Service - Compression Pressure Check. Compression Check
Q: Is the compression pressure normal?
YES : Go to Step 8.
NO : Repair it. Then confirm that the malfunction symptom is eliminated.
STEP 8. Check the positive crankcase ventilation system.
Refer to Positive Crankcase Ventilation System Check. System Check
Q: Is the positive crankcase ventilation system normal?
YES : Go to Step 9.
NO : Repair it. Then confirm that the malfunction symptom is eliminated.
STEP 9. Check the evaporative emission control system.
Refer to Purge Control System Check (Purge Flow Check) Purge Flow Check.
Q: Is the evaporative emission control system normal?
YES : Check the following item, and repair or replace the defective item.
a. Check if the injectors are clogged.
Then confirm that the malfunction symptom is eliminated.
NO : Repair it. Then confirm that the malfunction symptom is eliminated.