Inspection Procedure 23
COMMENT- The test is failed when the air/fuel ratio is not controlled to the ideal air/fuel ratio. This occurs due to the feedback control by heated oxygen sensor signals, insufficient EGR flow rate, or deteriorated catalyst.
NOTE: If the three-way catalyst temperature is low when checking the exhaust gas, the three-way catalyst cannot sufficiently clean the emissions. Warm up the engine sufficiently before checking the exhaust, and check immediately
TROUBLESHOOTING HINTS
The most likely causes for this case:
- Malfunction of air/fuel ratio control system.
- Malfunction of the EGR system.
- Deteriorated catalyst.
DIAGNOSIS
Required Special Tool:
MB991502: Scan Tool (MUT-II)
STEP 1. Check the exhaust gas with the engine at normal operating temperature.
1. Check that the engine is at normal operating temperature.
If warmed up, go to Step 2.
If not warmed up, warm up the engine completely before checking the exhaust gas.
STEP 2. Check the following items.
1. Check the following items.
a. Check all vacuum hoses and connectors.
b. Check electrical wires and connectors for obvious problems.
c. Check the exhaust system for missing or damaged parts.
If not malfunctioning, go to Step 3.
If malfunctioning, repair or replace. Then confirm that the malfunction symptom is eliminated.
STEP 3. Check the drive-ability.
Carry out a test drive.
If normal, go to Step 4.
If not normal, Symptom Chart
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
STEP 4. Using scan tool MB991502, read the diagnostic trouble code (DTC).
If DTC is not output, go to Step 5.
If DTC is output, go to Trouble Code Diagnostic Procedures.
STEP 5. Check the ignition timing.
Refer to On-vehicle Service.
If within specifications, go to Step 6.
If not within the specifications, check that the crankshaft position sensor and timing belt cover are in the correct position.
Then confirm that the malfunction symptom is eliminated.
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
STEP 6. Using scan tool MB991502, check data list.
1. Check the following items in the data list.
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).
If the checks above meet the specifications, go to Step 7. If the checks above do not meet the specifications, repair or replace. Then confirm that the malfunction symptom is eliminated.
CAUTION: To prevent damage to the scan tool, turn the ignition switch "OFF" before connecting or disconnecting the scan tool.
STEP 7. Using scan tool MB991502, check data list item 11: Heated Oxygen Sensor (front).
- Voltage should fluctuate between 0 - 0.4 volts and 0.6- 1.0 volts while idling after the engine has been warmed.
If the voltage fluctuates correct, go to Step 8. If the voltage does not fluctuate, go to Step 10.
STEP 8. Check the EGR system.
Refer to Emission Control System.
If correct, go to Step 9.
If incorrect, repair or replace. Then confirm that the malfunction symptom is eliminated.
STEP 9. Check the idle mixture.
Refer to On-Vehicle Service.
Standard value: CO contents 0.5% or less.
If within specifications, go to Step 11.
If not within specifications, replace the heated oxygen sensor (front). Then confirm that the malfunction symptom is eliminated.
STEP 10. Check the fuel pressure.
If correct, go to Step 11.
If incorrect, repair or replace. Then confirm that the malfunction symptom is eliminated.
STEP 11. Check the following items.
1. Check the following items, and repair or replace the defective items.
a. Check the injectors for operation sound.
b. Check the injectors for fuel leakage.
c. Check the ignition coils, spark plugs, spark plug cables.
d. Check compression.
e. Check the positive crankcase ventilation system.
f. Check the evaporative emission control system.
2. Then check the malfunction symptom.
If the malfunction symptom is eliminated, the check is completed.
If the malfunction symptom has not been resolved, replace the catalytic converter. Then confirm that the malfunction symptom is eliminated.