P0427: Catalyst Temperature Sensor Circuit Low Bank 1 Sensor 1
What to do
Usually driveable with no symptom beyond the warning light.
What this code means
The bank 1 catalyst temperature sensor signal has fallen below its plausible range. As with most thermistor circuits, the reading direction and the wiring fault are related in a way worth knowing: a short to ground usually produces one extreme and an open circuit the other, and which is which depends on whether the sensor's resistance rises or falls with temperature.
Unplugging the sensor and observing which way the reported value jumps identifies the circuit's behaviour in seconds and tells you what an open looks like on this particular engine.
Likely causes
Start here
- Faulty catalyst temperature sensor · moderate
- Signal wire shorted to ground · moderate
- Corroded or loose connector · easy
Less common
- Damaged wiring harness near exhaust heat · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0427.