What it means
Catalyst temperature sensor at bank 1 sensor 1 reads in range but plausibility check fails — slow response or stuck reading.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The bank 1 sensor 1 catalyst temperature sensor reports temperature near the upstream side of the catalytic converter. The control module checks whether its reading changes plausibly as the exhaust warms and operating conditions change; P0426 sets when the signal stays within the expected electrical range but responds too slowly or appears stuck.
Common causes
Most likely first.
- Sensor drift
- Sensor element aged beyond calibration window
- Sensor mounting loose - signal damping
Symptoms
- Check engine light on
- Failed emissions inspection
- Possibly slightly increased fuel consumption
- Sulfur (rotten egg) smell from exhaust under load
How to diagnose it
- Record freeze-frame data and compare bank 1 sensor 1 temperature readings with engine temperature and other available exhaust temperature data to see whether the signal is implausible or static.
- With the engine cold, inspect the bank 1 sensor 1 mounting and connector for looseness, damage, corrosion, or contamination that could damp the response.
- Inspect the sensor lead and nearby harness for heat damage, rubbing, or strain, then check whether the sensor reading changes smoothly as the exhaust warms.
- Use a scan tool to monitor the sensor during a controlled warm-up and compare its response with the manufacturer's expected behavior.
- If the mounting and wiring are sound, test the sensor and its circuit against the manufacturer's specification before considering a control-module fault.
Common fixes
- Secure a loose bank 1 sensor 1 mounting or connector.
- Repair damaged or poorly connected wiring at the sensor.
- Replace the bank 1 sensor 1 catalyst temperature sensor if its response is out of specification.
- Repair or replace the control module only if its circuit checks confirm an internal fault.
Can I keep driving?
Usually, a short trip is possible if the engine runs normally, but avoid heavy loads if you notice a sulfur smell or worsening fuel use. The fault can affect emissions monitoring and may cause an inspection failure; stop if the exhaust smell becomes strong or the vehicle loses power.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.