P0422 — Warm Up Catalyst Efficiency Below Threshold (Bank 1)
Drive with caution — fix soon.
What P0422 means
This code means the warm-up catalytic converter on bank 1 has fallen below its required efficiency, judged by the oxygen sensors monitoring it. The cause can be a degraded catalyst, a failing oxygen sensor, an exhaust leak, or an engine running problem feeding it too much fuel. Repairs range from a simple sensor replacement to replacing the catalytic converter.
Common symptoms
- Check engine light is on
- Failed emissions or smog test
- Slight decrease in fuel economy
- Sulfur or rotten-egg smell from exhaust
- Occasional mild loss of power
Common causes
- Degraded or failing warm-up catalytic converter
- Faulty downstream oxygen sensor
- Exhaust leak near the catalyst
- Engine misfire or overly rich fuel mixture
- Catalyst contaminated by oil or coolant
Typical repair cost
$200 – $1500
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0422 code?
Usually yes, for the short term. The car typically drives normally, but emissions are elevated and you'll fail a smog test. Diagnose it soon so the underlying cause doesn't lead to bigger repairs.
How much does it cost to fix a P0422 code?
Anywhere from about $200 for a sensor or exhaust-leak repair to $1,500 or more if the warm-up catalytic converter must be replaced.
Is a P0422 code serious?
It's moderate. You won't be stranded immediately, but it indicates an emissions fault, and an unresolved root cause like a misfire can continue degrading the catalyst.
What's the difference between P0422 and a regular catalyst code?
P0422 specifically flags the warm-up (close-coupled) catalyst on bank 1, which sits closer to the engine to light off quickly. The diagnosis approach is similar to other catalyst efficiency codes.