P0420 on Ford: Catalyst System Efficiency Below Threshold (Bank 1)
Severity: 2 of 4
Usually safe to drive for a short time if the light is steady and the car runs normally. Fix the cause before it gets worse, because a converter that is overheating from misfires can become a fire risk and will fail completely. If the light flashes, or you smell strong sulfur or see a glowing red converter, park it.
Estimate range covers the repairs listed below; see the cost breakdown. A flashing check engine light, a hot temperature gauge, or brakes that feel different mean stop driving and get help.
What P0420 usually means on a Ford
P0420 on Ford vehicles commonly appears at high mileage on trucks and SUVs. Exhaust manifold leaks can cause both a ticking noise and a false catalyst reading.
Most likely causes on Ford vehicles
- Exhaust manifold leak or broken studs
- Rear oxygen sensor
- Misfire history
- Worn converter
Order reflects cost and likelihood in general; your vehicle may differ. Confirm with testing before buying parts.
Ford specific tips
- A ticking noise on cold start that fades as the engine warms suggests a manifold leak.
- Fix misfires first.
Estimated repair cost
This is an estimate, built from typical parts price ranges plus labor hours times an assumed shop rate of $110 to $190 per hour. Actual prices vary by vehicle, region, and shop. Diagnosis fees are often extra.
| Repair | Parts | Labor | Estimate (low / high) |
|---|---|---|---|
| Rear oxygen sensor | $30 to $120 | 0.3 to 1.0 h | $30 + 0.3 × $110 = $63 $120 + 1.0 × $190 = $310 |
| Exhaust gasket or flex pipe repair | $15 to $150 | 0.5 to 1.5 h | $15 + 0.5 × $110 = $70 $150 + 1.5 × $190 = $435 |
| Catalytic converter (aftermarket, direct fit) | $250 to $1,400 | 1.0 to 2.5 h | $250 + 1.0 × $110 = $360 $1,400 + 2.5 × $190 = $1,875 |
Costs are generic for this code; parts and labor on some Ford models may run higher.
Watch a repair video
P0420 How To Diagnose A Bad Catalytic Converter (EricTheCarGuy). Third-party video, loads from YouTube (privacy-enhanced mode) only when you press play. Procedures vary by vehicle. Search YouTube for “P0420 Ford fix” videos.
Repair manuals
Step-by-step service manuals for Ford with torque specs and wiring diagrams:
Haynes manuals for Ford Chilton manuals
Affiliate disclosure: links in this box may earn FixOrPark a commission at no extra cost to you.
Check Ford recalls
Enter your VIN at the NHTSA recall lookup before paying for repairs.
FAQ
Can a manifold leak cause P0420 on my Ford?
Yes. Air drawn in near the sensors confuses the reading.
Read the full P0420 guide or more Ford check engine notes.