P0426 Catalyst Temperature Sensor Range/Performance Bank 1 Sensor 1

P0426 points to a range or performance issue in Catalyst Temperature Sensor Bank 1 Sensor 1. The temperature signal exists but does not match expected catalyst behavior.

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 treat P0426 as catalyst failure until sensor response and circuit integrity are checked.

Symptoms of P0426

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 P0426

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

Compare Bank 1 Sensor 1 catalyst temperature to coolant temperature, exhaust temperature, engine load, heater command, and freeze-frame data.
Inspect sensor response speed, connector heat damage, wiring resistance, sensor placement, exhaust leaks, and catalyst heat-up behavior.
Check whether the signal is slow, biased, noisy, or inconsistent with actual exhaust temperature changes.

Related OBD-II codes

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