Test Hf: Catalyst Efficiency Monitor & Exhaust Systems: Testing

NOTE: For additional testing information, see DIAGNOSTIC AIDS .

NOTE: Ignition timing retarded below specification may increase exhaust gas temperature and decrease catalyst efficiency over time. Ensure customer has not refueled vehicle with leaded gasoline or experienced high vehicle oil consumption.

1) DTC P0420: Check For Misfire Monitor DTCs
DTC P0420 indicates HO2S-12 switching frequency increases to its specified limit value, or switching frequency ratio of HO2S-11 and HO2S-12 approach a specified limit value. Possible causes are as follows:
- Damaged pre-catalyst (California only).
- Damaged warm-up 3-way catalyst.
- Damaged exhaust pipe.
- Intake air leaks.
- Faulty fuel injectors.
- Fuel injector leaks.
- Fuel pressure too high.
- Cylinder misfiring.
- Damaged or faulty spark plug.
- Incorrect ignition timing.
- Oil contamination.
- Damaged HO2S.
- HO2S-12 wires improperly connected.
Ensure ignition timing is correct. Connect scan tool to DLC. Using scan tool, retrieve all DTCs. If misfire DTCs are not present, go to next step. If any misfire DTC(s) P0300-P0306 are present, isolate cylinder and repair as necessary. See TEST HD , step 1).

NOTE: ECT sensor DTCs can be an indication that thermostat is not operating correctly or that coolant level is not filled to specifications, producing above normal operating temperatures.

2) Check ECT Sensor DTCs
If DTC P0115 is present in step 1) , go to TEST DA , step 1). If DTC P0115 is not present in step 1) , go to next step.

3) Check For Any Other DTCs

If any DTCs other than P0420 were present in step 1) , service as necessary before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If P0420 was the only DTC present in step 1) , go to next step.

4) Check Fuel Delivery System

Perform fuel delivery system diagnostic procedure. See TEST HC , step 1). If fuel delivery is okay, go to next step. If fuel delivery is not okay, repair as necessary.

NOTE: If a catalyst is in series with a leaking exhaust system, it can fail Catalyst Efficiency Monitor test.

5) Check For Obvious Leaks In Exhaust System
Inspect entire exhaust system for cracks, leaks, loose connections or holes. Repair or replace as necessary. If exhaust system is okay, go to next step.

6) Check For Obvious Restrictions In Exhaust System

Inspect exhaust system for collapsed areas, dents, excessive bending or damaged muffler. Repair or replace as necessary. If exhaust system is okay, go to next step.

NOTE: Vacuum gauge reading may be normal when engine is first started. However, excessive restriction in exhaust system will cause vacuum gauge needle to drop to a low point when engine is left idling.

7) Check Manifold Vacuum For Indication Of Excessive Exhaust Restriction
Connect vacuum gauge to intake manifold vacuum source. Connect scan tool to DLC. Using scan tool, access RPM PID from PID/DATA MONITOR & RECORD menu. Observe vacuum gauge needle while starting engine and raising engine speed to 2000 RPM. Decrease engine speed to base idle RPM. Manifold vacuum should rise to more than 16 in. Hg at 2000 RPM. If manifold vacuum is okay, leave vacuum gauge and scan tool connected and go to next step. If manifold vacuum is low, an excessive restriction may be present. Go to step 9).

8) Check Manifold Vacuum For Indication Of Moderate Exhaust Restriction

Using scan tool, access RPM PID from PID/DATA MONITOR & RECORD menu. With transmission in Neutral, start engine and increase and maintain engine speed at 2000 RPM while monitoring engine vacuum. Allow engine to return to idle speed. On a non-restricted system, manifold vacuum should quickly increase to normal range (about 16 in. Hg) as high RPM is maintained. On a restricted system, manifold vacuum will slowly increase to normal range as high RPM is maintained. If manifold vacuum is low or slow to respond, go to next step. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If no restriction is found and you were directed here to diagnose DTC P0420, replace ineffective catalytic converter. Ensure proper routing of HO2S-12. If directed here to diagnose a symptom and symptom still exists, return to SYMPTOM DIAGNOSIS under SYMPTOMS in TROUBLE SHOOTING - NO CODES - VILLAGER article.

NOTE: An intake manifold gasket leak can also cause vacuum gauge needle to remain well below normal range.

9) Check Manifold Vacuum With Exhaust Manifold Disconnected For Indication Of Restriction
Remove exhaust pipe from exhaust manifold. Repeat step 8). If manifold vacuum is now 16 in. Hg, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST .

10) Check Manifold Vacuum With Muffler/Tailpipe Disconnected For Indication Of Restriction

Disconnect muffler/tailpipe assembly from rear of catalytic converter. Repeat step 8). If manifold vacuum is 16 in. Hg now, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom. Repeat QUICK TEST .