Open or damaged heater element inside the Bank 1 Sensor 2 oxygen sensor itself, which is the most common cause on higher-mileage BMW engines; Corroded, backed-out, or damaged pins in the oxygen sensor connector or the corresponding DME harness connector; Broken or chafed heater circuit wiring between the sensor and the DME, often near the exhaust manifold heat shield or along the transmission tunnel; Blown fuse that supplies the oxygen sensor heater circuit, sometimes shared with other emissions-related components; Failed DME heater driver circuit, which is rare but possible after a short circuit or water intrusion into the electronics box; High resistance in the heater circuit ground path, typically at a chassis ground point near the engine or transmission

DTC codes / BMW codes / P1139

P1139 · BMWO2 Sensor Heater Circuit High Voltage Bank 1 Sensor 2

Q: What does code P1139 mean?

O2 Sensor Heater Circuit High Voltage Bank 1 Sensor 2. P1139 on a BMW means the engine computer (DME) has detected an abnormally high voltage on the heater circuit for the post-catalyst oxygen sensor on Bank 1, which is Sensor 2. The heater is designed to bring the sensor up to operating temperature quickly, and a high-voltage reading tells the DME that the circuit is drawing too little current or is open, so the sensor will not heat properly and closed-loop fuel control may be affected.

P1139 on a BMW means the engine computer (DME) has detected an abnormally high voltage on the heater circuit for the post-catalyst oxygen sensor on Bank 1, which is Sensor 2. The heater is designed to bring the sensor up to operating temperature quickly, and a high-voltage reading tells the DME that the circuit is drawing too little current or is open, so the sensor will not heat properly and closed-loop fuel control may be affected.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
A slight increase in fuel consumption because the post-catalyst sensor stays cold and the DME may run a richer default mixture
Occasional rough idle or hesitation when the engine is cold, as the sensor does not reach operating temperature quickly
A stored pending or confirmed fault code that returns shortly after being cleared
In some cases, a noticeable delay in the oxygen sensor readiness monitor completing during an emissions test
No drivability complaints at all when the heater circuit fails open but the sensor signal itself remains intact

Common causes, most likely first

Open or damaged heater element inside the Bank 1 Sensor 2 oxygen sensor itself, which is the most common cause on higher-mileage BMW engines
Corroded, backed-out, or damaged pins in the oxygen sensor connector or the corresponding DME harness connector
Broken or chafed heater circuit wiring between the sensor and the DME, often near the exhaust manifold heat shield or along the transmission tunnel
Blown fuse that supplies the oxygen sensor heater circuit, sometimes shared with other emissions-related components
Failed DME heater driver circuit, which is rare but possible after a short circuit or water intrusion into the electronics box
High resistance in the heater circuit ground path, typically at a chassis ground point near the engine or transmission

How to diagnose and fix it

Clear the fault code and verify with a scan tool that P1139 returns, then check the freeze-frame data to confirm the engine was cold when the fault set
Inspect the Bank 1 Sensor 2 oxygen sensor connector and the DME harness connector for corrosion, loose pins, or pushed-out terminals, and repair as needed
Measure the resistance of the oxygen sensor heater element across the two heater pins with a multimeter and compare to BMW specifications; an open circuit confirms a failed sensor
Check the heater circuit fuse and verify battery voltage is present at the sensor connector with the key on and engine off
Perform a voltage drop test on the heater ground circuit and the power feed to rule out high-resistance wiring before condemning the sensor
If wiring and fuses are good but the heater resistance is out of spec, replace the Bank 1 Sensor 2 oxygen sensor with a quality OEM or equivalent part
After repair, clear the codes, run the engine through a complete drive cycle, and confirm the oxygen sensor heater monitor and the post-catalyst monitor both pass

What a high-voltage heater code really means

A high-voltage code on a heater circuit almost always means the circuit is open or has excessive resistance, not that the sensor is receiving too much voltage, so technicians who chase a short to power waste time.
The post-catalyst sensor on BMW engines often fails its heater element long before the sensing element degrades, so a P1139 does not automatically mean the sensor's signal is inaccurate.
A corroded connector pin at the sensor can mimic a failed heater element, and replacing the sensor without inspecting the plug often leads to the same code returning within a few days.
On some BMW models the oxygen sensor heater fuse is shared with the secondary air pump or another emissions component, so a blown fuse may set additional codes that point away from the real problem.
The DME may set P1139 only during a cold-start heater test, so a sensor that works fine when warm can still be the cause and should be tested when the engine is at ambient temperature.

Can I keep driving with P1139?

You can usually continue driving with P1139 because the engine will still run, but the post-catalyst sensor will not heat properly and fuel economy or emissions may suffer. Avoid long periods of idling and have the fault diagnosed soon, especially if you need to pass an emissions inspection.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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