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Home / DTC / P1156 — O2 Sensor Heater Circuit Low Voltage Bank 2 Sensor 2

P1156 — O2 Sensor Heater Circuit Low Voltage Bank 2 Sensor 2

Detailed page for trouble code P1156.

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Code

P1156

BMW P — Powertrain

O2 Sensor Heater Circuit Low Voltage Bank 2 Sensor 2

Brand: BMW
Type: P — Powertrain
AI status
Completed
ready
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Page language: EN

Causes

  • Failed downstream O2 sensor heater element (open or high resistance)
  • Blown fuse or faulty heater relay/power supply
  • Open/short or high resistance in heater wiring or corroded connector pins
  • Poor or missing ground at sensor or PCM driver issues
  • Water intrusion or damage to sensor connector
  • PCM or heater driver circuit fault (less common)

Symptoms

  • MIL (Check Engine Light) on
  • Possible failed emissions test or catalytic efficiency monitor failure
  • Delayed catalyst light‑off and worse cold‑start emissions
  • Usually no immediate drivability loss, but can cause long‑term fuel trim/emissions issues
  • Occasional P0157/P0141 etc. stored alongside heater code

What to check

  • Retrieve freeze frame and live data for Bank 2 Sensor 2 heater status with a scan tool
  • Visual inspection of sensor, wiring harness, and connector for corrosion, damage, or water intrusion
  • Check relevant fuses and relays for the O2 heater circuit
  • Back‑probe sensor connector to confirm presence of heater supply voltage with key ON and when heater is commanded ON
  • Measure heater element resistance at the sensor (with sensor unplugged)
  • Perform wiggle test of harness while monitoring heater voltage/current or scan tool status

Signal parameters

  • Typical heater supply voltage (key ON, engine OFF): ~11–14 V (varies by model)
  • Heater resistance (typical range for many O2 sensors): ~2–20 ohms (model dependent)
  • Heater current when energized: ~0.5–3 A (depends on sensor design)
  • PCM may use ground‑side switching or PWM to control heater—observe supply vs. switched side when commanded ON
  • Values vary by sensor/manufacturer — compare to BMW service spec when available

Diagnostic algorithm

  1. Read and record freeze frame, all stored codes and live heater status for Bank 2 Sensor 2.
  2. Visually inspect sensor and connector for corrosion, melted insulation, or water entry. Repair/clean as required.
  3. With key ON (engine OFF), back‑probe the sensor connector: verify heater supply voltage on the feed pin (should be near battery voltage) and check the control/return pin while commanding heater ON with a scan tool.
  4. Unplug sensor and measure heater element resistance at sensor pins. Compare to expected range (consult service data). Very high/open indicates failed heater.
  5. If supply is missing, check fuses/relays and continuity of power feed to the sensor connector.
  6. If supply present but control/ground not switching, trace continuity to PCM and check for short to ground/power or open circuit. Wiggle harness while monitoring.
  7. If wiring and power/ground are good but heater open or out of spec, replace the Bank 2 Sensor 2. Recheck and clear codes.
  8. If replacement does not clear or heater circuit driver faults persist, test/replace PCM only after confirming wiring and grounds are good and performing manufacturer‑recommended PCM checks.
  9. After repair, confirm heater current/voltage and that the PCM no longer reports the code; verify via road test and monitor O2 sensor status.

Likely causes

  • Open or high‑resistance heater element in Bank 2 Sensor 2 (most common)
  • Damaged wiring or corroded connector at the sensor
  • Blown fuse or defective heater relay/power feed
  • PCM driver or ground fault (after wiring ruled out)

Fault status

⚠️ Status
O2 heater circuit low voltage detected for Bank 2 Sensor 2 — heater supply/driver or heater element has insufficient voltage/current.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2 hours

Similar codes

P0037 P0052 P0141 P0157 P1157
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