What does code P1138 mean?

Q: What does code P1138 mean?

O2 Sensor Heater Circuit Low Voltage Bank 1 Sensor 2. P1138 on a BMW indicates that the engine control module (DME) has detected a low voltage condition on the heater circuit for the downstream oxygen sensor on bank 1, which is sensor 2 after the catalytic converter. The DME monitors the heater current and expects a specific voltage drop; when the voltage stays below the threshold, it flags the circuit as faulty, often due to a failed heater element or wiring issue.

DTC codes / BMW codes / P1138

P1138 · BMWO2 Sensor Heater Circuit Low Voltage Bank 1 Sensor 2

P1138 on a BMW indicates that the engine control module (DME) has detected a low voltage condition on the heater circuit for the downstream oxygen sensor on bank 1, which is sensor 2 after the catalytic converter. The DME monitors the heater current and expects a specific voltage drop; when the voltage stays below the threshold, it flags the circuit as faulty, often due to a failed heater element or wiring issue.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.