Emissions

P0043 — HO2S Heater Control Circuit Low (Bank 1, Sensor 3)

Severity: low Safe to drive

What P0043 means

The engine computer switches a heater inside the oxygen sensor so it reaches operating temperature quickly and reads exhaust gas accurately. P0043 sets when the heater control circuit for Bank 1, Sensor 3 (usually located after the catalytic converter) shows lower voltage than expected. Typical causes are a wiring open or short to ground, a failed sensor heater, a blown fuse, or a faulty driver in the PCM.

Symptoms

  • Check engine light on
  • Increased exhaust emissions
  • Slightly higher fuel consumption possible
  • Rough running on cold start
  • Unstable idle (uncommon)
  • Failed emissions test

Possible causes

  1. Failed heater element in the Bank 1 Sensor 3 oxygen sensor
  2. Damaged wiring or connector in the heater circuit (open, chafing, corrosion)
  3. Heater control wire shorted to ground
  4. Blown fuse or faulty relay feeding the sensor heater
  5. Failed heater driver inside the PCM (rare)

How to diagnose

  1. Scan the codes, note freeze frame data, clear the code and see if it returns
  2. Inspect the wiring and connector at Bank 1 Sensor 3 for damage, heat marks and corrosion
  3. Check the fuse and relay that power the oxygen sensor heaters
  4. Measure the sensor heater resistance and compare it with the spec for your vehicle
  5. Check for power and the control signal at the connector with the ignition on and engine warm
  6. Test the control wire for opens and shorts to ground back to the PCM
  7. Look for exhaust leaks near the sensor
  8. If wiring and sensor are good, test the PCM

Common fixes

  • Replace the faulty oxygen sensor
  • Repair damaged wiring or replace the connector
  • Replace the fuse or relay (after finding why it failed)
  • Repair or replace the PCM if the heater driver is confirmed faulty

Questions and answers

What does P0043 mean?

It means low voltage in the heater control circuit of the Bank 1 Sensor 3 oxygen sensor. The heater helps the sensor start working sooner after a cold start.

Can I drive with code P0043?

Usually yes for a short time, as it won't harm the engine. Emissions may be higher and the light will stay on, so repair it soon.

How do I fix P0043?

Start with the fuse, wiring and sensor connector, then check the heater resistance. Most often the fix is a new sensor or a wiring repair.

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.