Question 1

What does P0138 mean?

Accepted Answer

P0138 - O2 Sensor Circuit High Voltage (Bank 1 Sensor 2). Downstream O2 sensor on bank 1 reading consistently high voltage (rich).

Question 2

What are the symptoms of P0138?

Accepted Answer

Check engine light, May accompany P0420

Question 3

What causes P0138?

Accepted Answer

Faulty downstream O2 sensor, Rich running condition, Short in wiring

Question 4

How much does it cost to fix P0138?

Accepted Answer

Typical repair cost: $80-$250. A downstream sensor reading high can indicate catalyst efficiency issues or a sensor stuck rich.

P0138 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)

Don't guess — diagnose P0138 the right way