What it means
Catalyst temperature sensor at bank 1 sensor 2 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 2 catalyst temperature sensor reports temperature at the downstream sensor position on bank 1. The control module expects the reading to respond plausibly as exhaust conditions change; P042B sets when the signal remains electrically in 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
- Save freeze-frame data and compare the bank 1 sensor 2 reading with engine temperature and other available exhaust temperature data to spot a static or implausible value.
- Inspect the downstream bank 1 sensor mounting and connector for looseness, corrosion, contamination, or damage that could damp the signal.
- Check the sensor lead and harness for heat damage, rubbing, or strain, particularly along the route near the exhaust.
- Monitor the sensor on a scan tool during warm-up and changing engine load to see whether its reading responds as expected.
- If the wiring and mounting are sound, test the sensor response against the manufacturer's specification before considering a module fault.
Common fixes
- Secure the bank 1 sensor 2 mounting or connector if loose.
- Repair damaged or poorly connected wiring at the sensor.
- Replace the bank 1 sensor 2 temperature sensor if its response is out of specification.
- Repair or replace the control module only if circuit testing confirms an internal fault.
Can I keep driving?
A short trip is usually possible if the engine runs normally, but avoid heavy loads if you notice sulfur odor or worsening fuel use. The fault can interfere with emissions checks and may cause an inspection failure.
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.