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P0158 Generic (SAE)

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

Updated 2026-10-02 · Fuel & air metering

Severity
Low
Typical repair cost
40 – 300 EUR
System
Powertrain

What it means

The downstream oxygen sensor on bank 2 (the bank without cylinder 1) is reporting a voltage above about 0.9-1.0 V, or a value a zirconia cell cannot generate on its own (above 1.1 V). A reading near 0.9 V can be a genuinely rich bank 2; anything higher means the signal wire is picking up voltage from the heater supply or another source, usually through melted insulation or a water-filled connector.

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Symptoms

  • Check engine light with normal or near-normal driveability
  • Strong fuel or sulphur smell from the bank 2 side of the exhaust if the bank is really rich
  • Companion rich codes P0152 or P0175 when the cause is fuelling
  • Catalyst monitor incomplete for bank 2
  • Occasionally a slightly rough idle on vehicles that trim fuel from the rear sensor

Common causes

  1. Signal wire shorted to the 12 V heater wire inside a heat-damaged pigtail
  2. Water or coolant in the connector bridging signal to heater supply
  3. Genuinely rich bank 2 from a leaking injector or faulty upstream sensor
  4. Misfire on bank 2 sending unburned fuel through the catalyst
  5. Sensor contaminated with coolant or oil ash, biasing it rich
  6. Wrong sensor or incorrect wiring after a previous repair

How to diagnose

  1. Read live B2S2 voltage: anything above 1.1 V cannot come from the sensor and proves an external voltage source – inspect the pigtail for melted insulation and open the connector for water
  2. Compare with B2S1 and the bank 2 fuel trims: if the upstream sensor is also high and long-term trim is below -10%, bank 2 is genuinely rich and the rear sensor is simply telling the truth
  3. Unplug the sensor: the scan tool should fall back to the 0.45 V bias; if it stays high, the harness or ECU side carries the short
  4. Measure resistance between each heater pin and the signal pin on the sensor side (should be infinite) and on the harness side (should be infinite with the key off); any continuity locates the short
  5. Measure heater resistance (2-15 ohm) and heater supply voltage (12-14 V with the key on) to confirm the heater is not the component that failed
  6. If the fault is intermittent, wiggle the harness under the car with the engine running while watching the voltage trace

Frequently asked questions

The reading is 1.2 V – can the sensor do that?

No. A zirconia sensor tops out around 1.0 V. A higher value means the signal wire is touching a voltage source, almost always the heater wire in a damaged pigtail.

Why does a rich bank matter if the engine runs fine?

Sustained rich exhaust overheats the catalyst and can melt its substrate; a 300-900 EUR catalyst is a much bigger bill than the 60-120 EUR sensor.

Could the fault be in the bank 1 sensor instead?

Not for this code. P0158 is specific to bank 2 sensor 2; bank 1 downstream faults are P0136-P0141.

Related codes

P0156P0157P0161P0152P0138P0175

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