P0425 Catalyst Temperature Sensor Bank 1 Sensor 1

P0425 indicates an issue with Catalyst Temperature Sensor Bank 1 Sensor 1. The controller is not receiving a believable temperature signal for the Bank 1 catalyst monitor.

Code details

Generic OBD-II · P0

System: Emissions
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the catalyst for P0425 until the temperature sensor circuit and plausibility have been verified.

Symptoms of P0425

Check-engine light, often with no obvious change in how the car drives.
A failed emissions test or incomplete readiness monitors.
Sometimes a faint fuel-vapour smell (on EVAP codes).

Common causes of P0425

A worn catalytic converter or an oxygen/air-fuel sensor reading out of range.
EVAP leaks — a loose or failed gas cap, cracked hose, or purge/vent valve.
Exhaust leaks, fuel-trim problems, or a fault in a related monitor.

Useful checks before replacing parts

Check catalyst temperature sensor Bank 1 Sensor 1 data, reference voltage, ground, signal wiring, freeze-frame temperature, and related circuit codes.
Inspect connector heat damage, exhaust routing, sensor placement, wiring insulation, corrosion, and signs of impact or contamination.
Compare sensor readings during cold start and warm operation to expected ambient and exhaust temperature behavior.

Related OBD-II codes

These nearby emissions entries can help compare wording and pin down the fault area.