Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the exhaust system and downstream HO2S.

Internal damage of a catalytic converter is usually caused by abnormal engine operation upstream of catalyst. Conditions that produce higher than normal temperatures in the catalytic converter, such as cylinder misfire, are likely suspects.

1. 1) DTC P0420 Or P0430: Check Possible Cause Of Misfire
   
   DTC P0420 indicates bank one catalyst system efficiency is below minimum requirement. DTC P0430 indicates bank 2 catalyst system efficiency is below minimum requirement. Possible causes are:
   • Use of leaded fuel.
   • Oil contamination.
   • Cylinder misfire.
   • Fuel pressure too high.
   • HO2S sensor improperly connected.
   • Damaged exhaust system component.
   • Faulty ECT sensor.
   • Faulty HO2S.

   Retrieve all Continuous Memory DTCs. If misfire codes are not present, go to next step. See MISFIRE DIAGNOSTIC TROUBLE CODES (DTC)  table. If any misfire codes are present, isolate cylinder and repair as necessary.

   NOTE: Non-California applications do not have an HO2S monitor. A Catalyst Efficiency Monitor DTC can be generated for a rear HO2S concern. To check for a rear HO2S concern, go to CIRCUIT TEST H , step 81). If any repairs are made, perform KOER ON-DEMAND SELF-TEST . If no repairs were necessary, go to step 3).
2. 2) Check HO2S Monitor DTCs
   
   If DTCs P0136, P0138, P0141, P0156, P0158 or P0161 were present in step 1), perform appropriate circuit test. See DIAGNOSTIC TROUBLE CODE (DTC) REFERENCE CHART . If none of these DTCs are present in step 1), go to next step.
3. 3) Check ECT Sensor DTCs
   
   If DTCs P0117, P0118, P0125 or P1117 were present in step 1), perform appropriate circuit test. If none of these codes are present in step 1), go to next step.
4. 4) Check For Other DTCs
   
   If any DTCs except P0420 and P0430 are present in step 1), perform appropriate circuit test. If no DTCs except P0420 and/or P0430 are present in step 1), go to next step.
5. 5) Check Rear HO2S Wiring Harness
   
   Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair as necessary. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Also check PCM pins. If PCM pins are damaged, replace PCM. If wiring harness and connectors are okay, go to next step.
6. 6) Check Fuel Pressure
   
   Turn ignition off. Release fuel pressure. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. Turn ignition off. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC .
7. 7) Check For Exhaust System Leaks
   
   If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair as necessary. If exhaust system is okay, go to next step.
8. 8) Check For Exhaust System Restrictions
   
   Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step.
9. 9) Check Manifold Vacuum
   
   Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11).
10. 10) Check Manifold Vacuum For Exhaust Restriction
    
    Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non-restricted system, manifold vacuum increases quickly to normal range as increased RPM is maintained. On a restricted system, manifold vacuum increases slowly to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step.
11. 11) Check Manifold Vacuum
    
    Leave tachometer and vacuum gauge connected. Disconnect exhaust pipe from exhaust manifold. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, 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 as necessary.
12. 12) Check Manifold Vacuum
    
    Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair as necessary. If manifold vacuum is still not okay, fault is in catalytic converter. Repair as necessary. Check tailpipe/muffler assembly for debris from catalytic converter.