P0424 — Heated Catalyst Efficiency Below Threshold (Bank 1)
Drive with caution — fix soon.
What P0424 means
This code means the heated catalytic converter on bank 1 isn't reaching the efficiency the computer expects, so your exhaust isn't being cleaned properly. It often points to an aging or failing catalytic converter, but can also be caused by a faulty oxygen sensor or an exhaust leak fooling the readings. A proper diagnosis usually checks the sensors and exhaust first, since replacing the converter is the most expensive fix.
Common symptoms
- Check engine light is on
- Reduced fuel economy
- Failed emissions or smog test
- Slight loss of power or sluggish acceleration
- Faint sulfur or rotten-egg smell from the exhaust
Common causes
- Worn or failing catalytic converter
- Faulty downstream oxygen (O2) sensor
- Exhaust leak near the catalyst or sensors
- Engine misfire or rich fuel mixture damaging the catalyst
- Faulty catalyst heater circuit or wiring
Typical repair cost
$200 – $2200
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0424 code?
Usually yes, for normal short-term driving the car will run fine. But the converter isn't doing its job, so you'll pollute more and likely fail an emissions test. Get it diagnosed within a week or two to avoid bigger problems.
How much does it cost to fix a P0424?
If it's just an oxygen sensor or an exhaust leak, repairs often run $200 to $500. If the catalytic converter itself needs replacing, expect anywhere from $900 to $2,200 depending on the vehicle.
Is a P0424 code serious?
It's not an emergency and won't usually leave you stranded, but it shouldn't be ignored. A weak catalyst means more emissions and can slowly worsen, so it's best to address it before it leads to a costly converter replacement.
Does P0424 always mean I need a new catalytic converter?
No. Sometimes the real culprit is a bad oxygen sensor, an exhaust leak, or an unaddressed misfire. A good shop will rule those out first, since they're far cheaper to fix than the converter.