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DTC codes / BMW codes / P1133

P1133 · BMWO2 Sensor Heater Control Circuit Bank 2 Sensor 1

P1133 on a BMW indicates that the engine control module (DME) has detected a fault in the heater circuit for the pre-catalytic oxygen sensor on bank 2, sensor 1. The DME monitors the heater element's current draw and response time, and sets this code when the circuit is open, shorted, or drawing current outside the expected range.

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.
  • Rough idle or hesitation during cold starts, as the sensor takes longer to reach operating temperature.
  • Slightly increased fuel consumption because the DME may default to open-loop fueling longer than normal.
  • Intermittent misfire or poor driveability when the engine is cold, especially in damp conditions.
  • A stored pending code or freeze-frame data showing the fault occurred during warm-up.
  • In rare cases, a sulfur or rotten-egg smell from the exhaust if the sensor heater fails and the sensor remains cold.

Common causes, most likely first

  1. Failed oxygen sensor heater element (open circuit or shorted internally).
  2. Damaged or corroded wiring harness between the DME and the oxygen sensor heater circuit.
  3. Blown fuse or faulty relay supplying power to the oxygen sensor heater circuit.
  4. Loose or contaminated connector pins at the oxygen sensor or DME.
  5. Water intrusion into the sensor connector or harness, causing corrosion and high resistance.
  6. Aftermarket oxygen sensor with incorrect heater resistance or poor quality control.
  7. DME internal driver failure for the heater circuit (rare but possible).

How to diagnose and fix it

  1. Clear the code and perform a road test to see if it returns; note any freeze-frame data.
  2. Visually inspect the oxygen sensor connector and wiring for damage, corrosion, or water intrusion.
  3. Check the heater circuit fuse and relay, and verify power and ground at the sensor connector with a multimeter.
  4. Measure the resistance of the oxygen sensor heater element and compare to BMW specifications.
  5. Check for continuity and resistance in the wiring between the sensor and DME; repair any opens or shorts.
  6. If the heater circuit tests good, substitute a known-good oxygen sensor and recheck.
  7. After repair, clear codes and verify the heater circuit monitor completes with a scan tool.

Heater Circuit Faults Often Misdiagnosed

  • A P1133 can be set by a heater circuit that is electrically intact but slow to respond, so resistance testing alone may not reveal the fault.
  • Corrosion inside the oxygen sensor connector is a common cause on BMWs, especially in regions with road salt, and is often overlooked during diagnosis.
  • The DME may set this code only during cold-start conditions, so a test drive after clearing codes must include a cold soak to reproduce the fault.
  • Replacing the oxygen sensor without checking the heater circuit fuse and relay can lead to a repeat failure if the root cause is upstream.
  • Some aftermarket oxygen sensors have heater resistances that fall outside BMW's narrow specification, triggering P1133 even when the sensor appears to function.

Can I keep driving with P1133?

You can usually drive the vehicle with P1133, but avoid prolonged cold-start idling and heavy acceleration until the fault is repaired, as the engine may run richer and fuel economy will suffer. Have the circuit diagnosed soon to prevent catalytic converter damage from unburned fuel.

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.

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