P0427 Catalyst temperature sensor: signal or voltage too low (bank 1, sensor 1)

By: Diagno editorial team · Updated: 2026-10-15

P0427 means: Catalyst temperature sensor: signal or voltage too low (bank 1, sensor 1). The exhaust pressure or temperature sensor tells the computer the exhaust gas pressure or temperature. Drive gently and have the car checked soon. The repair usually costs about €60–300 in Estonia.

What it means

The exhaust pressure or temperature sensor tells the computer the exhaust gas pressure or temperature. The turbo, particulate filter and emission cleaning are controlled by it. The signal voltage is too low. Usually a wire is broken, a connector is loose or a wire is shorted to ground.

What you may notice

• Engine light on
• Particulate filter regeneration doesn't start
• The car may go into limp mode

What could be wrong

1. 1Connector loose, damp or corroded
2. 2Wire broken or shorted to ground
3. 3Faulty sensor
4. 4Engine computer fault (rare)

Repair difficulty: Easy

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Check that the sensor hoses are intact and fitted the right way round. You can do the simpler checks yourself.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the sensor

Standard SAE description: Catalyst Temperature Sensor Low (Bank 1, Sensor 1)