P0430: Catalyst System Efficiency Below Threshold (Bank 2)
TL;DR
P0430 = catalytic converter efficiency low on Bank 2 (only on engines with two banks). Severity: medium. Drivable short-term; fails emissions. Top causes: worn converter (55%), bad rear O2 sensor Bank 2 (30%), exhaust leak (10%). Cost: $150 DIY (sensor) to $1,400 (converter).
Can I keep driving with P0430?
IF the check engine light is steady → you can drive short-term; you will fail emissions and may lose a little fuel economy. IF the light flashes or you also have misfire codes → stop and fix the misfire first, since raw fuel can destroy the converter.
Symptoms
- Check engine light on (steady)
- Failed emissions test
- Slightly reduced fuel economy
- Occasional sulfur smell
- Usually no change in how the car drives
Top causes (ranked by probability)
| Likely cause | Probability | Notes |
|---|---|---|
| Worn or failing catalytic converter (Bank 2) | 55% | Common at high mileage |
| Faulty downstream (rear) O2 sensor on Bank 2 | 30% | Check first — cheaper |
| Exhaust leak near the Bank 2 sensors | 10% | |
| Unresolved misfire / fuel-trim issue | 5% |
What does P0430 mean?
Technical explanation
On a two-bank engine the ECM evaluates the oxygen-storage capacity of each bank’s catalytic converter by comparing upstream and downstream oxygen-sensor signals. When the Bank 2 downstream sensor begins to mirror the upstream signal, the converter on that bank has dropped below the efficiency threshold and P0430 is set (Bank 2 = the bank not containing cylinder 1).
In simple terms
Your engine has two sides, each with its own exhaust scrubber (catalytic converter). P0430 means the scrubber on the second side (Bank 2) isn’t working well. It’s the same problem as P0420, just the other side of the engine.
How to diagnose P0430 (step by step)
- Scan and record all codes. Fix any misfire (P030x) or fuel-trim codes first — they cause P0430.
- Identify Bank 2. Confirm which side is Bank 2 for your engine before replacing parts.
- Check for exhaust leaks. Inspect the Bank 2 manifold and pipes near the sensors.
- Compare O2 sensor data. A Bank 2 downstream sensor switching like the upstream one points to a dead converter.
- Test the rear O2 sensor. Replace a sluggish sensor before condemning the converter.
Repair options & cost
- Replace the Bank 2 downstream oxygen sensor (try first)
- Repair exhaust leaks near the sensors
- Replace the Bank 2 catalytic converter (CARB-compliant)
- Fix the root cause (misfire / fuel trim) first
| DIY cost | $40–$250 |
|---|---|
| Workshop cost | $200–$1,400 |
| Repair time | 30 min (O2 sensor) to 2 hours (converter) |
Costs are local ballpark ranges and vary by region and vehicle.
Tools you’ll need
- OBD-II scanner (BlueDriver / ANCEL)
- O2 sensor socket set
- Penetrating oil
Vehicle-specific notes
- Only V6/V8/“V” engines (and some boxer engines) have a Bank 2 — inline-4s do not.
- Often appears together with P0420 if both converters are aging.
- Use a CARB-compliant direct-fit converter to avoid a quick re-trigger.
Common mistakes to avoid
- Replacing the converter before testing the cheaper rear O2 sensor
- Confusing Bank 1 and Bank 2 and working on the wrong side
- Ignoring an underlying misfire that will ruin the new converter
- Fitting a cheap non-compliant converter
Frequently asked questions
What is the difference between P0420 and P0430?
They are the same low-catalyst-efficiency fault on different cylinder banks: P0420 is Bank 1, P0430 is Bank 2. P0430 only appears on engines that have two banks.
Can I drive with P0430?
Yes, short-term, with a steady light and no misfires. You will fail an emissions test until it is repaired.
Will a new O2 sensor fix P0430?
Sometimes — about 30% of the time the Bank 2 rear sensor is the cause. Test it before replacing the costly converter.
P0430 summary
| Meaning | Catalytic converter efficiency low (Bank 2) |
|---|---|
| Severity | Medium |
| Safe to drive? | Yes, short-term (unless misfiring) |
| Top cause | Worn converter (55%) |
| DIY cost | $40–$250 |
| Shop cost | $200–$1,400 |