2008 Jeep P0420: What It Means & Is It Safe to Drive?
P0420 on the 2008 Jeep: Catalyst System Efficiency Below Threshold (Bank 1). Here's what it means, what usually causes it, what repairs typically cost, and whether it's safe to keep driving.
What this code means
The downstream oxygen sensor detects that the catalytic converter is not storing or converting exhaust properly. This is one of the most common check engine codes.
Common causes on the 2008 Jeep
- Failed or aging catalytic converter
- Faulty downstream oxygen sensor
- Exhaust leak before or after the catalyst
- Engine misfire or rich/lean condition damaging the catalyst
Symptoms
- Check Engine Light on
- Often no drivability issues
- Possible failed emissions test
- Rotten egg smell in some cases
Typical fixes
- Replace catalytic converter
- Replace oxygen sensor(s)
- Repair exhaust leaks
- Fix underlying fuel/ignition issues first
Repair cost range
For a 2008 Jeep, repairs for P0420 typically fall between $400 and $2400, depending on the root cause and labor rates in your area.
Known issues on Jeep
Jeep P0420 on the 3.6L Pentastar V6 is one of the most common catalytic converter failures in its segment—cats typically fail between 100k–150k miles. Jeep and RAM share this engine; the cat heat shield rattles before the converter fully fails, which is an early warning sign. Grand Cherokee and Cherokee use dual converters (P0420 = bank 1, P0430 = bank 2); budget for replacing both simultaneously since the second cat usually follows within 20k miles. Always verify the downstream O2 sensor connector is intact—they corrode from road salt exposure.
Most commonly affected models