Code
P1152
BMW
P — Powertrain
O2 Sensor Heater Circuit Low Voltage Bank 2 Sensor 1
Views:
UK: 18
EN: 40
RU: 29
AI status
Completed
Completed
100%
Causes
- Open or high-resistance wiring in heater supply or ground
- Blown fuse or faulty relay supplying heater circuit
- Corroded/bent/damaged sensor connector or pins
- Failed O2 sensor heater element
- Poor chassis or engine ground affecting heater return
- PCM/heater driver fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Longer catalyst warm-up time and higher cold emissions
- Reduced fuel economy or rough cold idle
- Possible failed emissions test
- Heater-related freeze-frame PIDs showing low voltage/current
What to check
- Retrieve freeze-frame and live data using a scan tool — monitor O2 heater status, supply voltage, and duty cycle
- Confirm code is current (not pending) and note freeze-frame conditions (battery voltage, engine temp)
- Visually inspect Bank 2 Sensor 1 connector and harness for damage, corrosion, pin push-out, or water intrusion
- Check relevant fuses and relays for continuity and proper operation
- Back-probe sensor connector with key ON (engine OFF) to check for battery feed on heater supply pin
- With engine running and heater active, measure voltage at heater supply and ground; observe changes as PCM applies power
Signal parameters
- Expected heater supply voltage (key ON) ≈ battery voltage: ~11–14 V
- Heater resistance (typical narrowband O2 heater): roughly 2–15 Ω (varies by sensor) — consult BMW spec for exact value
- Heater current when energized: up to several amps (0.5–5 A depending on sensor)
- PCM typically modulates heater duty cycle; during cold start duty cycle may be near 100% until warm
- If measured supply voltage is significantly below battery or not switching, suspect supply/fuse/relay or open
Diagnostic algorithm
- Connect a capable scan tool, read DTC(s), view freeze-frame and live PIDs for Bank 2 Sensor 1 heater voltage/current and related parameters.
- Visually inspect the Bank 2 Sensor 1 connector and wiring harness for corrosion, damage, pin corrosion, or water ingress; repair as needed.
- With ignition ON (engine OFF), back-probe the heater supply terminal at the sensor connector and verify battery voltage is present (or as specified). If missing, check relevant fuse/relay and trace supply back to source.
- Unplug sensor and measure heater resistance across heater pins with a DVOM. Compare to BMW spec. Open or excessively high resistance indicates a failed heater element — replace sensor.
- With sensor connected and engine running (or during cold start when heater is commanded), back-probe and measure voltage at the heater supply and ground while monitoring heater control duty cycle. If PCM is commanding but voltage is low, look for high-resistance connections or short to ground.
- Check ground continuity from sensor ground pin to chassis/engine ground; repair poor ground connections.
- Perform wiggle/operational checks of the harness while observing live data to identify intermittent faults.
- If wiring, connectors, fuses, and sensor check good, consider bench/loaded test of PCM driver or consult manufacturer technical service information before replacing control module.
- Clear codes and test drive to confirm repair; verify code does not return and heater parameters are within expected ranges.
Likely causes
- Failed heater element in Bank 2 Sensor 1 (most common)
- Open, short-to-ground, or high-resistance wiring at sensor connector
- Blown fuse or bad relay for oxygen sensor heater supply
- Corroded/loose connector or poor ground at sensor harness
- Faulty PCM heater driver (least common)
Fault status
Status
O2 sensor heater circuit low voltage — Bank 2 Sensor 1. Heater supply/current below expected range; inspect sensor, wiring, fuse/relay, grounds, and PCM heater driver.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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