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P0152 Generic (SAE)

O2 Sensor Circuit High Voltage (Bank 2, Sensor 1)

Updated 2026-10-02 · Fuel & air metering

Severity
Medium
Typical repair cost
40 – 450 EUR
System
Powertrain

What it means

The bank 2 upstream oxygen sensor signal is stuck above roughly 0.9-1.0 V, or sits at a voltage a zirconia sensor cannot physically produce (over 1.1 V). Either bank 2 is running very rich, or the signal wire has shorted to the heater supply or another 12 V source. Bank 2 is the cylinder bank that does not contain cylinder 1.

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Symptoms

  • Check engine light, often with P0172/P0175 rich codes
  • Black smoke and strong petrol smell from the exhaust
  • Fouled spark plugs on bank 2 cylinders and rough idle
  • Poor fuel economy
  • Catalyst overheating or sulphur smell if driven long with a rich bank

Common causes

  1. Signal wire shorted to the 12 V heater wire inside the sensor pigtail (common after heat damage)
  2. Leaking or stuck-open injector on a bank 2 cylinder
  3. Excessive fuel pressure from a faulty regulator
  4. Sensor contaminated with coolant (head gasket) or oil additives, giving a false high reading
  5. Misfire on bank 2 dumping unburned fuel past the sensor (the sensor still reads rich)
  6. Damaged sensor element or ECU input fault

How to diagnose

  1. Read the live B2S1 voltage: a reading above 1.1 V is impossible for the sensor itself and proves a short to a voltage source – inspect the pigtail where it passes the exhaust for melted insulation
  2. Check long-term fuel trim on bank 2: a value below -10% confirms a genuine rich condition; near 0% means the sensor or wiring is lying
  3. Unplug the sensor: the scan tool should drop to the 0.45 V bias; if it stays high, the harness or ECU side is at fault
  4. Measure heater resistance between the heater pins (2-15 ohm normal) and check for continuity between a heater pin and the signal pin – any continuity means an internal short
  5. Pull the bank 2 spark plugs: a single black, wet plug points to a leaking injector on that cylinder; measure injector coil resistance (11-16 ohm for a saturated-type injector) and compare across the bank
  6. Verify fuel pressure with the regulator vacuum line connected and disconnected; pressure must drop about 0.5 bar with vacuum applied

Frequently asked questions

Can a rich condition damage anything?

Yes. Prolonged rich running on one bank washes oil off the cylinder walls and can overheat and melt the bank 2 catalyst, which costs far more than the sensor.

The voltage reads 1.3 V – what does that mean?

A zirconia sensor cannot generate more than about 1.0 V, so 1.3 V proves the signal wire is picking up voltage from elsewhere, almost always the heater wire in a melted pigtail.

Should I replace both upstream sensors?

Not necessarily. If bank 1 switches normally and the car has under 150,000 km, replacing only bank 2 is reasonable.

Related codes

P0150P0151P0155P0175P0132

Nearby codes in this group