P0056: HO2S Heater Control Circuit (Bank 2 Sensor 2)

P0056 means HO2S Heater Control Circuit (Bank 2 Sensor 2). Oxygen sensors only produce a useful signal when they are hot, so they contain an electric heater. This code points to a problem in the heater circuit of the oxygen sensor on bank 2 (the side opposite cylinder 1), sensor 2 (downstream, after the catalytic converter). The control module has detected a fault in the circuit itself, such as an open circuit, a short, or a signal outside the electrical limits it expects.

CodeP0056
SystemOxygen sensor heater
SeverityLow
TypeGeneric powertrain

Can I keep driving? Safe to drive short-term, but have it checked to avoid failed emissions or worse fuel economy.

Common symptoms

  • Check engine light on
  • Usually no noticeable drivability change
  • Engine may take longer to enter closed-loop fuel control after a cold start
  • Can cause a failed emissions inspection

Possible causes

  • Burned-out heater element inside the oxygen sensor
  • Blown fuse for the heater circuit
  • Damaged wiring or connector (often near the exhaust)
  • Engine computer heater driver fault (rare)

How to diagnose P0056

  1. Check the fuse that supplies the oxygen sensor heaters.
  2. Unplug the sensor and measure heater resistance; compare with the service specification.
  3. Check for battery voltage on the heater supply wire with the engine running.
  4. Inspect the harness for melted or chafed sections near the exhaust.

What the code means, digit by digit

PPowertrain0Generic (SAE) code0Sub-system56Specific fault

Generic codes have the same definition on every OBD-II vehicle (petrol cars from model year 1996 in the US, 2001 in the EU; diesels later). Manufacturers can add their own enhanced codes; those are not listed here.

Related codes

General guidance only. Fault codes describe what the engine computer saw, not which part failed: confirm with testing before replacing parts, and follow the vehicle's service information.