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Home › Jeep › 2021 › Cherokee Trailhawk › Repair and Diagnosis › Engine Performance › System › 3.2L - DTCS P0300 To P054A › DTC Troubleshooting › P0420-Catalyst System Efficiency Below Threshold Bank 1 › Set Condition

Set Condition

If the ratio between the Downstream O2 Sensor and the Upstream O2 Sensor signals is more than approximately 0.6/1 (or 60%), the catalyst is determined to be failing.