P042B
Catalyst Temperature Sensor Circuit Range/Performance Bank 1 Sensor 2
Catalyst monitoring (emissions)
Generic OBD-II
Medium
What it means
P042B means the catalyst temperature sensor on bank 1 (sensor 2) is reporting a value that's out of its expected range or doesn't track with actual exhaust conditions. This sensor monitors converter temperature for emissions control and doesn't affect how the engine runs, so the practical effects are a check-engine light and disrupted emissions monitoring.
Medium
Can I keep driving? The engine drives normally — this is a monitoring sensor, so the main consequences are a check-engine light and a possible emissions-test failure.
Common symptoms
What you'll notice
- Check-engine light on
- Possible failed or incomplete emissions readiness
- Usually no change in how the engine drives
Common causes
Most likely first
- Faulty catalyst temperature sensor (bank 1, sensor 2)Likely
- Sensor reading out of plausible range or driftingCommon
- Chafed, open, or shorted wiring in the sensor circuitCommon
- Poor or corroded connection at the sensorLess often
- Faulty ECM (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the fault is the bank 1 sensor 2 catalyst temperature sensor circuit.
- Inspect the sensor's connector and wiring for heat damage, chafing, or corrosion.
- Compare the sensor's temperature reading against actual exhaust temperature and the other sensors.
- Check the signal, reference, and ground at the sensor against specification.
- Replace the catalyst temperature sensor if it reads implausibly. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P042B?+
Yes — the catalyst temperature sensor monitors exhaust temperature and doesn't control how the engine runs. Repair it to clear the light and restore emissions monitoring.
Can I just clear P042B?+
It will return until the sensor or its circuit is repaired. Clearing only resets the light.
Related codes
Often seen with P042B
Read & clear P042B yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX