Inspection Procedure 21

INSPECTION PROCEDURE 21: Too high CO and HC concentration when idling

COMMENT

- 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
- 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 the DTC set?

YES Refer to Diagnostic Trouble Code Chart Multiport Fuel Injection (MFI).

NO Go to Step 2.

STEP 2. Check the ignition timing.

Testing and Inspection.

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.
1. Item 6: Engine Coolant Temperature Sensor.

2. Item 5: Intake Air Temperature Sensor.

3. Item AC: Cylinder 1, 4 Heated Oxygen Sensor (front)

4. Item AD: Cylinder 1, 4 Heated Oxygen Sensor (rear)

5. Item AE: Cylinder 2, 3 Heated Oxygen Sensor (front)

6. Item AF: Cylinder 2, 3 Heated Oxygen Sensor (rear)

7. Item BB: Barometric Pressure Sensor
(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.
8. Item AC: Cylinder 1, 4 Heated Oxygen Sensor (front).

9. Item AE: Cylinder 2, 3 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. Are they 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.
10. Check the injectors for fuel leakage.

11. Check the ignition coil and spark plugs.

12. Check compression pressure.

13. Check the positive crank case ventilation system.

14. Check the evaporative emission system.

15. 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.