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Cherokee Trailhawk
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Repair and Diagnosis
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Engine Performance
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System
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3.2L - DTCS P0300 To P054A
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DTC Troubleshooting
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P0420-Catalyst System Efficiency Below Threshold Bank 1
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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.