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P0036 Generic (SAE)

HO2S Heater Control Circuit (Bank 1 Sensor 2)

Updated 2026-10-02 · Fuel, air metering & auxiliary emission controls

Severity
Low
Typical repair cost
20 – 250 EUR
System
Powertrain

What it means

Bank 1 sensor 2 is the downstream oxygen sensor after the catalytic converter on the cylinder-1 side; its only job is catalyst efficiency monitoring. The ECU checks the heater control circuit of this sensor and sets P0036 when the voltage or current feedback does not match the commanded state of the heater driver. The engine's fuel control is not affected, but the catalyst monitor cannot run, so the car will not pass an OBD readiness check.

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Symptoms

  • Check Engine light on with no drivability complaint
  • Catalyst monitor and O2 sensor monitor stay 'not ready'
  • Failed emissions / OBD inspection
  • Rear sensor voltage shown as fixed or slow to react in live data when cold
  • Sometimes accompanied by P0141 or P0420

Common causes

  1. Failed heater element in the bank 1 downstream sensor, commonly after many years of heat cycles
  2. Damaged harness along the underbody or near the catalyst heat shield (stone chips, rodents, rust abrasion)
  3. Blown heater fuse or faulty supply relay (shared with the other sensors)
  4. Corroded connector under the car exposed to road salt and water
  5. Exhaust leak or missing heat shield overheating the sensor and its wiring
  6. Faulty ECU heater driver (rare)

How to diagnose

  1. Check for other heater codes: if P0030/P0050/P0056 are present too, start with the shared heater fuse and relay in the engine bay fuse box.
  2. Locate bank 1 sensor 2 behind the first catalyst and inspect the harness and connector along the underbody for abrasion, corrosion and heat damage.
  3. Unplug the sensor and measure heater resistance: 2-15 ohm at 20 °C (most downstream thimble sensors 5-14 ohm). Open circuit means the sensor needs replacement.
  4. Key on, check supply at the harness connector: 12-14.5 V on the heater power pin. Check the control pin with a test lamp to supply: it should flicker when the engine runs as the ECU pulses the heater.
  5. Measure heater current at idle with a clamp meter: 0.8-2 A. Zero current with good voltage on both pins means the heater is open or the ECU is not switching.
  6. Confirm the control wire continuity to the ECU pin (under 1 ohm) and check for shorts to ground and to B+ with both connectors unplugged.

Frequently asked questions

Can I just ignore P0036 since the car drives fine?

Mechanically yes, but the catalyst monitor will never complete and the Check Engine light may hide a more serious code later. Downstream sensors are cheap and usually quick to replace.

Which sensor is bank 1 sensor 2?

The sensor after the catalytic converter on the side of the engine that contains cylinder 1. On inline engines it is the only rear sensor; on V engines check the manufacturer's bank definition.

Related codes

P0037P0038P0141P0030P0056

Nearby codes in this group