Catalyst Temperature Sensor Circuit Bank 1 Sensor 2
What it means
P042A means the ECM sees a problem in the circuit for the bank 1, sensor 2 catalyst temperature sensor. This sensor monitors how hot the catalytic converter runs so the ECM can protect it and verify it's working. The fault is usually the sensor or its wiring, and it rarely affects how the car drives, but it keeps the emissions monitor from completing.
Can I keep driving? Safe to keep driving in the short term — this is an emissions monitor fault — but it will prevent emissions readiness and should be repaired.
Real-world scan data
Appears alongside · share of P042A scans
Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.
Common symptoms
What you'll notice
- Check-engine light on
- Usually no noticeable change in how the car drives
- Catalyst monitor may not complete (readiness not set)
- Fails an emissions/smog test
Common causes
Most likely first
- Faulty catalyst temperature sensor (bank 1, sensor 2)Likely
- Open or shorted wiring in the sensor circuitCommon
- Poor or corroded connection at the sensor connectorCommon
- Loss of reference voltage or ground to the sensorLess often
- ECM fault (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the fault is on bank 1, sensor 2.
- Inspect the sensor connector and wiring for damage, heat, or corrosion.
- Check the circuit for opens/shorts and confirm reference and ground.
- Measure the sensor's resistance/response against spec.
- Replace the catalyst temperature sensor if it tests faulty; clear and re-test.
FAQ
Quick answers
Is it safe to drive with P042A?+
Can I just clear P042A?+
Related codes
Read & clear P042A yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.