What does P0422 mean?
The main catalytic converter on Bank 1 is reading below its efficiency threshold — but, like P0420, this often points to upstream causes (O2 sensors, exhaust leaks, misfires) before the converter itself.
Quick Decision Guide
- Aging upstream or downstream O2 sensor
- Exhaust leak between converter and downstream sensor
- Unresolved misfires damaging catalyst
When to stop driving
P0422 alone is not a stop-driving code. If accompanied by a flashing check-engine light or severe misfire, stop driving — misfires accelerate catalyst damage.
Reviewed by ratchit Automotive Solutions for clarity and inspection-first safety framing. Not a substitute for professional diagnosis.
Repair Decision & Cost Guide
Use this guide to decide what to inspect first, what it may cost, and when to move from DIY checks to professional diagnosis.
P0422 does not automatically mean the catalytic converter has failed. It may involve O2 sensor behavior, exhaust leaks, fuel trim, or unresolved misfires — inspect upstream causes before replacing the converter.
DIY vs. Shop
Can you keep driving?
Best first DIY check
Don't replace this first
When to seek a shop
Recommended next action
Estimated Repair Cost
Inspection cost
$0–$25 DIY scanner
Shop diagnostic cost
$80–$150 (typical shop diagnostic fee)
Shop repair cost
$100–$2,500
Diagnostic uncertainty: This code points to a system or condition, not a guaranteed failed part. Inspect before replacing.
Cost variation: Costs vary by vehicle, location, part quality, labor rate, and the confirmed root cause.
Inspect Before Replacing
These checks are cheap, fast, and rule out the most common causes before spending money on parts.
- 1Scan for any companion misfire, O2, or fuel-trim codes — address those first.
- 2Inspect exhaust integrity between the converter and the downstream O2 sensor.
Track this emissions issue
Save this issue to My Garage, track what you inspect, and build service history for this vehicle.
V-IQ readiness preview: Medium impact — resolving and tracking this issue may improve your V-IQ readiness. Tracking active codes and resolutions builds a service history we use to estimate V-IQ readiness over time.
Understanding P0422 in detail
P0422 is closely related to P0420 and is used by some manufacturers to specifically flag the main (rear) catalyst on Bank 1 when a vehicle has both a warm-up catalyst and a main catalyst. The diagnostic logic is the same: the ECM compares upstream and downstream O2 sensor signals and decides catalyst efficiency is below its threshold. Just like P0420, P0422 should never be treated as an automatic catalytic converter replacement. Inspect O2 sensor behavior, exhaust leaks, fuel trim, and unresolved misfires before assuming the converter is the failed part.
Symptoms of P0422
- Check engine light on
- Vehicle fails emissions inspection
- Slightly reduced fuel economy
- Possible faint sulfur smell
Common causes
- Aging upstream or downstream O2 sensor
- Exhaust leak between converter and downstream sensor
- Unresolved misfires damaging catalyst
- Engine running rich or burning oil
- Genuine catalyst degradation (last on the list)
How to diagnose P0422
Steps ordered by urgency — tackle Now items first.
- NowScan for any companion misfire, O2, or fuel-trim codes — address those first.
- NowInspect exhaust integrity between the converter and the downstream O2 sensor.
- SoonView live upstream and downstream O2 sensor data — a healthy catalyst keeps the downstream signal flat.
- LaterReplace the main Bank 1 catalytic converter only after upstream causes have been ruled out.
How to fix P0422
Fixes listed in order of likelihood and cost-efficiency.
- 1Repair exhaust leaks
- 2Replace aging O2 sensors
- 3Address misfires or rich-running condition
- 4Replace main Bank 1 catalytic converter
Want to check your full vehicle?
Run a free maintenance scan to see what else needs attention based on your year, make, model, mileage, and climate.
Recommended tools & parts
These recommendations appear because this issue commonly requires inspection in this system area. ratchit does not recommend replacing parts until the likely cause is confirmed.
O2 Sensor & Catalyst Inspection Kit
Confirm O2 sensor behavior and exhaust integrity before replacing the catalytic converter
Check O2 sensor behavior before replacing the catalytic converter Verify fitment for your year/make/model.
Sensor & Diagnostic Kit
Test and replace common engine sensors — O2, MAF, cam/crank
Check sensor behavior before replacing parts Verify fitment for your year/make/model.
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Estimated Repair Cost — P0422
Ranges vary by vehicle, region, and shop. Use as a ballpark — always get a quote.
DIY estimate
$25 – $100
Shop estimate
$150 – $400
DIY estimate
$20 – $80
Shop estimate
$100 – $400
DIY estimate
$200 – $600
Shop estimate
$800 – $2,500
Cost data is estimated and may not reflect your specific vehicle or location.
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Frequently Asked Questions
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