P0042
HO2S Heater Control Circuit Bank 1 Sensor 3
Oxygen sensor (heater)
Generic OBD-II
Medium
What it means
P0042 indicates a fault in the heater control circuit of the bank 1, sensor 3 oxygen sensor — the third, rearmost sensor found on some exhaust layouts. The heater warms the sensor for accurate readings; a circuit fault leaves the car driving normally but turns on the check-engine light and can stop emissions monitors from completing.
Medium
Can I keep driving? Yes — the engine runs normally; this is a heater-circuit fault on the third (rearmost) O2 sensor, so the impact is the warning light and possible emissions-test failure.
Common symptoms
What you'll notice
- Check-engine light on
- Fails or can't complete an emissions/readiness test
- No noticeable change in drivability in most cases
Common causes
Most likely first
- Failed heater element in the bank 1, sensor 3 oxygen sensorLikely
- Open, short, or high-resistance in the heater control circuitCommon
- Corroded or loose sensor connectorCommon
- Damaged wiring or a blown heater fuseLess often
- Faulty ECM (rare)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and confirm the code points to bank 1, sensor 3.
- Locate the rearmost bank 1 O2 sensor and inspect its connector and wiring for damage or corrosion.
- Check the heater fuse and verify power at the sensor connector.
- Measure the sensor's heater resistance against spec.
- Replace the oxygen sensor if the heater element is faulty.
- Clear the code and complete a drive cycle to confirm the repair.
FAQ
Quick answers
Is it safe to drive with P0042?+
Yes, short-term — it doesn't affect running. It keeps the check-engine light on and can block emissions readiness, so schedule the fix.
Can I just clear P0042?+
It will reset once the ECM re-tests the heater unless the sensor or wiring problem is corrected.
Related codes
Often seen with P0042
Read & clear P0042 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