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EmissionsSeverity Medium: diagnose soon

P0138O2 Sensor Circuit High Voltage (bank 1 sensor 2)

What it means

The oxygen sensor bank 1 sensor 2 stays at a high voltage (rich reading) or above the possible range. The downstream sensor (after the catalyst) is mainly used to check how well the catalyst works.

Symptoms

  • Check engine light
  • Usually no change in how the car drives
  • Catalyst monitor may not complete

Common causes

  • Real rich condition (leaking injector, high fuel pressure, purge valve stuck open)
  • Signal wire shorted to the heater supply or to voltage
  • Contaminated sensor (coolant, oil or silicone)
  • Failed sensor

What to check first

  1. Check fuel trims and fuel pressure
  2. Create a vacuum leak: a good sensor drops below 0.2 V
  3. Check the signal wire for a short to the heater circuit
Can I drive with P0138? Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.

Generic OBD-II meaning. Manufacturer-specific meanings and checks can differ; always check the service information for the car.

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P0138: questions and answers

What does P0138 mean?

P0138: O2 Sensor Circuit High Voltage (bank 1 sensor 2). The oxygen sensor bank 1 sensor 2 stays at a high voltage (rich reading) or above the possible range. The downstream sensor (after the catalyst) is mainly used to check how well the catalyst works.

What are the symptoms of P0138?

Check engine light. Usually no change in how the car drives. Catalyst monitor may not complete.

What causes P0138?

Real rich condition (leaking injector, high fuel pressure, purge valve stuck open). Signal wire shorted to the heater supply or to voltage. Contaminated sensor (coolant, oil or silicone). Failed sensor.

How do you diagnose P0138?

1. Check fuel trims and fuel pressure 2. Create a vacuum leak: a good sensor drops below 0.2 V 3. Check the signal wire for a short to the heater circuit

Can I drive with P0138?

Usually yes for a short distance, but performance or economy may suffer and the fault can get worse. Diagnose it soon.