P0042

HO2S Heater Control Circuit Bank 1 Sensor 3

Q: 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.

Q: Can I just clear P0042?

It will reset once the ECM re-tests the heater unless the sensor or wiring problem is corrected.

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.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

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
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.

Read & clear P0042 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX