Emissions

P0142 — O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 3)

Severity: low Safe to drive

What P0142 means

An oxygen sensor needs to be hot to work, so it has a built-in electric heater that the ECU switches on. P0142 means the ECU detected a problem in the heater circuit of the Bank 1 Sensor 3 oxygen sensor, which sits downstream of the main catalytic converter (on some makes it is the second sensor after the catalyst). The usual causes are a burnt-out heater element, open or shorted wiring, or a poor connector contact.

Symptoms

  • Check Engine light on
  • Slightly higher fuel consumption possible
  • Increased exhaust emissions
  • Uneven idle (uncommon)
  • Failed emissions test

Possible causes

  1. Burnt-out oxygen sensor heater element
  2. Open, shorted or corroded wiring and connector pins
  3. Damaged or melted harness near the exhaust
  4. Blown fuse or faulty relay in the heater power supply
  5. Exhaust leak near the sensor (contributing factor)
  6. ECU fault (unlikely)

How to diagnose

  1. Scan for codes and freeze frame data and look for other oxygen sensor codes
  2. Inspect the sensor harness and connector for melting, chafing, corrosion or broken wires
  3. Check the heater fuse and power supply using the vehicle wiring diagram
  4. Measure the sensor heater resistance with a multimeter and compare it to specification
  5. Check for power and the ECU control signal (ground side) at the connector with ignition on
  6. Test the wires back to the ECU for opens and shorts
  7. Look for exhaust leaks near the sensor
  8. Review live sensor data and fuel trims to rule out related mixture problems

Common fixes

  • Replace the Bank 1 Sensor 3 oxygen sensor
  • Repair or replace the damaged wiring or connector
  • Replace the blown fuse or faulty relay
  • Fix the exhaust leak near the sensor
  • ECU diagnosis, reprogramming or replacement (last resort)

Questions and answers

What does P0142 mean?

It indicates a fault in the heater circuit of the Bank 1 Sensor 3 oxygen sensor. The ECU does not see the expected response from the heater, so the sensor may warm up slowly or not work correctly.

Can I drive with a P0142 code?

Usually yes, because it is not an emergency fault. Still, repair it soon because of emissions, possible higher fuel use and the risk of failing an inspection.

Do I always need to replace the sensor for P0142?

No. Check the fuse, wiring and connector first. If power and ground are present but the heater resistance is out of spec, the sensor needs replacing.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.