Smog & Emissions
P0420 Catalyst Efficiency Code Repair
P0420 doesn't always mean converter. We test before we quote.
P0420 (and P0430 on the other bank) means the computer no longer sees enough difference between the upstream and downstream oxygen sensor signals. A tired converter is one cause — so are a lazy rear O2 sensor, an exhaust leak ahead of the sensor, or a misfire.
We compare sensor waveforms, check for leaks, and confirm catalyst efficiency before recommending anything. That's the difference between a $180 repair and a $1,400 one.
What's included
P0420 Repair at our Murrieta shop
- Upstream and downstream O2 waveform comparison
- Exhaust leak and back-pressure testing
- Misfire and fuel trim analysis
- CARB-compliant converter replacement when justified
- Drive cycle and retest to confirm the code stays gone
Where to find us
Murrieta Smog Star — 26500 Jefferson Ave, Unit D, Murrieta, CA 92562. Serving Murrieta, Temecula, Wildomar, Menifee and Lake Elsinore.
Questions
Straight answers
Can I just clear the code?
It will return, and clearing it also resets the monitors, which fails the smog test.
Will P0420 fail a smog check?
Yes — the check engine light being on is an automatic failure.
How much is the diagnosis?
Call for our current diagnostic rate; it applies toward the repair.
Related services
Smog Check Murrieta
Walk-in smog checks at a licensed STAR station on Jefferson Ave.
ViewSTAR Certified Smog Station
A licensed STAR station — we can certify the cars test-only shops cannot.
ViewSTAR Smog Test Murrieta
State-directed STAR testing done right the first time.
ViewSmog Check Near Me
Minutes from I-15 on Jefferson Ave, serving Murrieta, Temecula, Wildomar and Menifee.
ViewFailed Smog Repair
We read your failure report, find the real cause, and retest free.
ViewGross Polluter Repair
STAR station certified to test and repair gross polluter vehicles.
ViewFree estimates · Free retest after qualifying smog repairs
Get a straight answer on your vehicle.
Tell us what it's doing. We'll tell you what it takes — in writing, before any work starts.