garajizOBD-II code · generic
P0421
Warm Up Catalyst Efficiency Below Threshold
- System
- P0 — Powertrain (generic)
- Severity
- Minor (2/5)
- Can I keep driving?
- Usually safe to drive
What does P0421 mean?
P0421 is defined as “Warm Up Catalyst Efficiency Below Threshold”.
You can usually keep driving, but have it checked soon so a small fault doesn’t become a bigger one.
Manufacturer-specific meanings
The same code can mean something different on some makes.
- Kia: Warm Up Catalyst Efficiency Below Threshold Bank 1
- Mitsubishi: Warm Up Catalytic Converter Bank 1 Efficiency Below Threshold
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This page is general information; an exact diagnosis needs measurements and a technician’s check.