P0042 HO2S Heater Control Circuit Bank 1 Sensor 3

P0042 indicates a heater control circuit fault for bank 1 sensor 3 heated oxygen sensor. The downstream heater control path is not behaving correctly.

Code details

Generic OBD-II · P0

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace the oxygen sensor before checking heater power, ground, and exhaust-side harness damage.

Symptoms of P0042

Check-engine light on, sometimes with rough or uneven running.
Hesitation, surging, or a noticeable change in fuel economy.
Occasionally hard starting or a smell of unburnt fuel.

Common causes of P0042

A failing or contaminated sensor (MAF, MAP, oxygen or air-fuel sensor).
Intake or vacuum leaks, or an exhaust leak near an upstream sensor.
Wiring, connector, or fuel-delivery problems that skew the reading.

Useful checks before replacing parts

Check heater feed voltage, ground or driver control, resistance, fuse supply, connector condition, and loaded circuit voltage.
Inspect wiring near exhaust heat, sensor connector pins, harness clips, and shared heater circuits for other oxygen sensor codes.
Compare heater command with sensor warm-up time and verify the fault occurs on bank 1 sensor 3, not another sensor position.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.