Inspection Procedure 22
INSPECTION PROCEDURE 22: Too High CO and HC Concentration When IdlingCOMMENT
- Abnormal air/fuel ratio is suspected.
TROUBLESHOOTING HINTS (The most likely causes for this case:)
- Malfunction of air/fuel ratio control system.
- Deteriorated catalyst.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B
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 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 in Ignition Timing.
Q: Is the ignition timing normal?
YES: Go to Step 3.
NO: Check that the crankshaft position sensor and timing belt cover are in the correct position. Then confirm that the malfunction symptom is eliminated.
STEP 3. Using scan tool MB991958, check data list.
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. Check the following items in the data list. Refer to, Data List Reference Table. Data List Reference Table & Normal Scan Data Values
a. Item 21: Engine Coolant Temperature Sensor.
b. Item 13: Intake Air Temperature Sensor.
c. Item 25: Barometric pressure Sensor.
d. Item 59: Heated Oxygen Sensor (rear).
e. Item 11: Heated Oxygen Sensor (front).
4. 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. Using scan tool MB991958, check data list.
1. Turn the ignition switch to the "ON" position.
2. Check the following items of the data list. Refer to, Data List Reference Table. Data List Reference Table & Normal Scan Data Values
a. Item 11: Heated Oxygen Sensor (front).
- Voltage should fluctuate between 0 - 0.4 volt and 0.6 - 1.0 volt while idling after the engine has been warmed.
3. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: Replace the heated oxygen sensor (front). Then confirm that the malfunction symptom is eliminated. If not resolved, go to step 6.
NO: Go to Step 5.
STEP 5. Check the fuel pressure.
Refer to On-vehicle Service Fuel Pressure Test. Testing and Inspection
Q: Is the fuel pressure normal?
YES: Go to Step 6.
NO: Repair or replace it. Then confirm that the malfunction symptom is eliminated.
STEP 6. Check the following items.
1. Check the following items, and repair or replace the defective items.
a. Check the injectors for fuel leakage.
b. Check the ignition coil, spark plugs and spark plug cables.
c. Check compression pressure.
d. Check the positive crank case ventilation system.
e. Check the evaporative emission system.
f. Check the EGR system.
2. Then check the malfunction symptom.
Q: Is the malfunction symptom eliminated.
YES: The check is completed.
NO: Replace the catalytic converter. Then confirm that the malfunction symptom is eliminated.