Note. For connector terminal identification, see CONNECTOR IDENTIFICATION . For circuit identification and wiring diagram, see CHEROKEE wiring diagram in WIRING DIAGRAMS article.
Note. DTC P0420: 1/1 CATALYTIC CONVERTER EFFICIENCY is monitored after engine warms up to 147°F (63.8°C), throttle has been open for 180 seconds at vehicle speed more than 20 MPH, with engine speed 1200-1700 RPM and MAP vacuum 15-20 in. Hg. DTC may be stored in Powertrain Control Module (PCM) when PCM senses catalyst efficiency deteriorated to a predetermined value. Possible causes are: exhaust leak, engine mechanical problem, defective catalytic converter or upstream Heated Oxygen Sensor (HO2S) older than downstream HO2S.
Note. 1/1 HO2S is located in upstream position.
- Turn ignition on, with engine off. Using scan tool, read DTCs. If DTC SPECIFIC GOOD TRIP COUNTER is displayed and displayed count is "0", go to step 3). If DTC SPECIFIC GOOD TRIP COUNTER is not displayed or displayed count is not "0", go to next step.
- At this time, DTC P0420: 1/1 CATALYTIC CONVERTER EFFICIENCY does not exist or is an intermittent problem. Using scan tool, read and record FREEZE FRAME data. Road test vehicle under conditions in FREEZE FRAME data, paying particular attention to fault setting conditions such as speed, temperature, load and MAP vacuum. Using scan tool, read DTCs. If DTC P0420: 1/1 CATALYTIC CONVERTER EFFICIENCY returns, go to next step. If DTC P0420: 1/1 CATALYTIC CONVERTER EFFICIENCY does not return, see INACTIVE DTC CONDITION. Test is complete.
- Start engine and allow it to idle. Check for exhaust leaks between engine and downstream HO2S. Repair exhaust system as necessary. Perform TEST VER-5A3. If exhaust system is okay, go to next step.
- Check exhaust system for excessive smoke caused by oil or coolant consumption. Repair engine mechanical condition as necessary and replace catalytic converter. Perform TEST VER-5A3. If engine mechanical condition is okay, go to next step. NOTE: A new downstream HO2S along with an aging upstream HO2S may cause DTC P0420: 1/1 CATALYTIC CONVERTER EFFICIENCY to set.
- If downstream HO2S has been replaced without replacing upstream HO2S, replace upstream HO2S. Perform TEST VER-5A3. If downstream HO2S has been replaced along with upstream HO2S, replace catalytic converter. Perform TEST VER-5A3.