Open circuit inside the oxygen sensor's heater (OBD-Codes.com; RepairPal lists oxygen sensor failure). Open power or ground wire to the oxygen sensor (OBD-Codes.com; RepairPal lists wiring issue). Corroded or broken exhaust system ground strap, on sensors grounded through the exhaust (OBD-Codes.com). Engine computer (PCM/ECM) failure (both sources).

Replace the Bank 2 Sensor 2 oxygen sensor if its heater is open; RepairPal lists this as the common repair. Repair damaged, loose or open heater power or ground wiring. Clean or replace a corroded or broken exhaust ground strap. Diagnose the engine computer only after the sensor and wiring test good.

P0056🌫 Emissions / oxygen sensorsDrive with caution, fix soon

P0056: HO2S Heater Control Circuit (Bank 2, Sensor 2) (Meaning, Causes, Fixes)

Q: What does P0056 mean?

P0056 means the engine computer has found a fault in the heater circuit of the rear (downstream) oxygen sensor on Bank 2, the one after the catalytic converter on the side of the engine without cylinder #1. An open heater inside the sensor, an open power or ground wire, or a corroded exhaust ground strap are the usual causes; a failed engine computer is also possible. Bank 2 Sensor 2 is the oxygen sensor after the catalytic converter on the side of the engine that does not contain cylinder #1, so this code only appears on V-type and flat engines with two banks. Oxygen sensors read accurately only when hot, so they have a built-in electric heater that warms them faster after a cold start. OBD-Codes.com explains that these sensors use three or four wires: two for the signal and the rest for the heater. Three-wire sensors are usually grounded through the exhaust system, while four-wire sensors have a separate ground wire, and the engine computer (or something it controls) supplies the heater's power or ground. RepairPal says the PCM sets P0056 when it detects that the heater wire is not operating. OBD-Codes.com says P0056 is basically identical to P0036, which is the same sensor position on Bank 1. P0057 and P0058 are the circuit-low and circuit-high versions for the same sensor. Note that the OBD-Codes.com page heading also labels the code 'B1S2', which conflicts with its own title and text; both sources and the standard definition place P0056 on Bank 2 Sensor 2.

Q: Can I keep driving with P0056?

Drive with caution, fix soon. Usually drivable. RepairPal rates P0056 Moderate: not an immediate safety threat, but get it diagnosed within a reasonable time. OBD-Codes.com says you probably won't notice anything besides the check engine light, because this downstream sensor mainly checks the catalytic converter. A car with an active check engine light will likely fail an OBD2 emissions inspection.

Reviewed 2026-10-24 · Based on 2 cited source(s)

What P0056 means

Bank 2 Sensor 2 is the oxygen sensor after the catalytic converter on the side of the engine that does not contain cylinder #1, so this code only appears on V-type and flat engines with two banks. Oxygen sensors read accurately only when hot, so they have a built-in electric heater that warms them faster after a cold start. OBD-Codes.com explains that these sensors use three or four wires: two for the signal and the rest for the heater. Three-wire sensors are usually grounded through the exhaust system, while four-wire sensors have a separate ground wire, and the engine computer (or something it controls) supplies the heater's power or ground. RepairPal says the PCM sets P0056 when it detects that the heater wire is not operating. OBD-Codes.com says P0056 is basically identical to P0036, which is the same sensor position on Bank 1. P0057 and P0058 are the circuit-low and circuit-high versions for the same sensor. Note that the OBD-Codes.com page heading also labels the code 'B1S2', which conflicts with its own title and text; both sources and the standard definition place P0056 on Bank 2 Sensor 2.

Severity: can I keep driving?

Drive with caution, fix soon

Usually drivable. RepairPal rates P0056 Moderate: not an immediate safety threat, but get it diagnosed within a reasonable time. OBD-Codes.com says you probably won't notice anything besides the check engine light, because this downstream sensor mainly checks the catalytic converter. A car with an active check engine light will likely fail an OBD2 emissions inspection.

Common symptoms

Check engine light on (both sources)
Probably no other noticeable symptom, since the heater only runs briefly after a cold start and the rear sensor does not feed the air/fuel calculation (OBD-Codes.com)
Decreased engine performance and increased fuel consumption (RepairPal; OBD-Codes.com disagrees, see FAQ)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Open circuit inside the oxygen sensor's heater (OBD-Codes.com; RepairPal lists oxygen sensor failure)
Open power or ground wire to the oxygen sensor (OBD-Codes.com; RepairPal lists wiring issue)
Corroded or broken exhaust system ground strap, on sensors grounded through the exhaust (OBD-Codes.com)
Engine computer (PCM/ECM) failure (both sources)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Find the right sensor: Bank 2 is the side of the engine without cylinder #1, and Sensor 2 is the one after the catalytic converter. OBD-Codes.com warns that a recently run exhaust gets very hot, so let it cool first.
Visually inspect the sensor wiring and connector for damaged or loose wires.
Unplug the sensor and, using a wiring diagram for your vehicle, measure the heater's resistance with a digital multimeter on the ohms scale. OBD-Codes.com says the heater should show some resistance; an excessive or over-limit (open) reading means the sensor needs replacing.
Back-probe the ground wire and check resistance to a known good ground. On three-wire sensors, check the exhaust ground strap for corrosion or breaks.
Back-probe the power wire with the meter on DC volts and check for power during a cold start. OBD-Codes.com says no power points to the supply circuit or the engine computer.

Typical fixes

Replace the Bank 2 Sensor 2 oxygen sensor if its heater is open; RepairPal lists this as the common repair
Repair damaged, loose or open heater power or ground wiring
Clean or replace a corroded or broken exhaust ground strap
Diagnose the engine computer only after the sensor and wiring test good

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The code comes back after a new sensor and good wiring checks, which points to the power supply or the engine computer
You don't have a multimeter and a wiring diagram for your vehicle
The old sensor is seized or breaks off in the exhaust pipe

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Will P0056 hurt performance or fuel economy?

The sources disagree. OBD-Codes.com says you probably won't notice anything but the check engine light, because the heater only runs briefly after start-up and the rear sensor mainly verifies catalytic converter efficiency rather than setting the air/fuel ratio. RepairPal lists decreased engine performance and increased fuel consumption as symptoms.

What's the difference between P0036 and P0056?

They describe the same fault on different sides of the engine. OBD-Codes.com says P0056 is basically identical to P0036, which is the Bank 1 Sensor 2 heater circuit (the side with cylinder #1); P0056 is the Bank 2 Sensor 2 heater circuit.

How is P0056 different from P0057 and P0058?

P0056 is the general heater-circuit fault for Bank 2 Sensor 2. RepairPal lists P0057 as the circuit-low and P0058 as the circuit-high versions for the same heater.

How much does it cost to fix P0056?

Neither source gives a price for this code. The usual repair is replacing one downstream oxygen sensor, so get a quote for that sensor on your vehicle once the wiring and ground strap have been checked.

Sources

Last reviewed 2026-10-24. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.