Emissions

P0038 — O2 Sensor Heater Control Circuit High (Bank 1, Sensor 2)

Severity: low Safe to drive

What P0038 means

The PCM switches the heater in the downstream (post-catalyst) Bank 1 oxygen sensor on and off by grounding it through an internal driver, so the sensor reaches operating temperature quickly. P0038 sets when the control circuit voltage stays higher than expected. Common reasons are a short to power in the wiring, a failed heater element, or a faulty driver inside the PCM.

Symptoms

  • Check Engine light on
  • Possible failed emissions test
  • Slightly higher fuel consumption in some cases
  • Rarely, an unstable idle
  • Often no other noticeable symptoms

Possible causes

  1. Failed heater element in the Bank 1 Sensor 2 oxygen sensor
  2. Damaged wiring or connector in the heater circuit
  3. Heater control wire shorted to battery voltage
  4. Open circuit in the heater wiring
  5. Faulty heater driver in the PCM (uncommon)

How to diagnose

  1. Read freeze frame data, clear the code and see if it returns
  2. Inspect the wiring and connector at the downstream sensor for melting, chafing, corrosion, oil or water
  3. Look for exhaust leaks near the sensor and wiring damaged by contact with the exhaust
  4. Measure the heater resistance and compare it with the factory spec
  5. Check the control wire for a short to power and for opens with the connector unplugged
  6. Confirm heater power supply, including the fuse and relay if the circuit has them
  7. Watch heater status and sensor voltage with a scan tool
  8. If the wiring and sensor are good, check the control signal at the PCM connector

Common fixes

  • Replace the Bank 1 downstream oxygen sensor
  • Repair the wiring or connector
  • Replace a blown fuse or faulty relay in the heater circuit
  • Repair or replace the PCM if the driver is faulty

Questions and answers

What does P0038 mean?

The PCM sees too high a voltage in the heater control circuit of the downstream oxygen sensor on Bank 1. The sensor itself or damaged wiring is the most common culprit.

Can I drive with code P0038?

Yes, for a short time it is normally safe. Still, fix it to avoid an emissions test failure and to keep other problems from being masked.

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.