Emissions

P0056 — Downstream O2 Sensor Heater Control Circuit, Bank 2 Sensor 2

Severity: low Safe to drive

What P0056 means

The engine control module powers a heater inside the Bank 2 downstream oxygen sensor so it reaches operating temperature quickly and reads accurately. P0056 sets when the heater circuit current, voltage or resistance is outside the expected range, such as an open, a short or a bad heater. The sensor or its wiring is the most common culprit.

Symptoms

  • Check engine light on
  • Slightly worse fuel economy
  • Possible rough running on a cold start
  • Higher exhaust emissions
  • Failed emissions inspection

Possible causes

  1. Failed heater element in the Bank 2 downstream oxygen sensor
  2. Open or shorted heater wiring, or a poor connector contact
  3. Blown fuse or missing power supply to the heater circuit
  4. Corroded terminals or a damaged harness near the exhaust
  5. Faulty heater driver in the ECM (rare)

How to diagnose

  1. Scan for codes and freeze frame data, and note any other oxygen sensor codes
  2. Check the fuse for the oxygen sensor heater circuit
  3. Inspect the Bank 2 Sensor 2 harness and connector for melting, chafing and corrosion
  4. Measure the sensor heater resistance and compare it to the factory spec
  5. Check for power and the control signal at the connector with the ignition on
  6. Test the wiring to the ECM for opens and shorts to ground or voltage
  7. Confirm you are on the correct sensor: Bank 2, downstream

Common fixes

  • Replace the Bank 2 downstream oxygen sensor
  • Repair or replace damaged wiring or the connector
  • Replace a blown fuse after finding why it failed
  • Repair or replace the ECM only after everything else is ruled out

P0056 on different brands

Ford · manuals
Ford may report an extended code P0056:1E tied to heater resistance monitoring; it describes the monitor condition detected, not a confirmed failed part.

Questions and answers

What does P0056 mean?

The ECM detected a fault in the heater circuit of the Bank 2 downstream oxygen sensor. The heater lets the sensor warm up fast and read correctly.

Can I drive with code P0056?

Yes, usually. It is not a safety issue, but fix it soon because emissions and catalyst monitoring are affected.

How do I fix P0056?

Start with the fuse, wiring and connector at the sensor. If those are fine and the heater resistance is out of spec, replace the sensor.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.