P0057
PowertrainHO2S Heater Control Circuit Low (Bank 2 Sensor 2)
Most of the time this is a small job, often just the rear oxygen sensor on bank 2 or a tired connector. The ECM runs a heater inside the sensor to bring it up to temperature quickly, and P0057 means it's seeing low voltage on that heater control circuit. It's the sensor sat after the cat on the side of the engine that doesn't have cylinder number one, so it monitors how well the cat is working rather than controlling fuel directly. Worth sorting because a dead heater means the sensor takes too long to start reading on a cold engine.
ⓘ Information only. This page provides general educational information about fault code P0057. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0057 mean?
P0057 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: HO2S Heater Control Circuit Low (Bank 2 Sensor 2).
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, frequently the only thing you'll actually notice
- • A small drop in fuel economy, usually a couple of mpg on shorter cold trips
- • Slightly rougher running from cold while the sensor warms up the slow way
- • Higher emissions readings if you happen to be near an MOT or emissions check
- • On some cars, no symptoms at all beyond the dash light
Possible causes
Causes commonly associated with P0057, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed heater element inside the bank 2 sensor 2 oxygen sensor, the usual offender as these wear out with age and heat cycling
- 2. Corroded or damaged connector at the sensor, water gets into the plug and the pins go green
- 3. Blown fuse feeding the sensor heaters, quick to check and cheap to put right
- 4. Chafed or broken wiring in the harness running back to the sensor, common where it's routed near the exhaust
- 5. High resistance on the control wire from the ECM, often a poor earth or a tired splice
- 6. ECM heater driver fault, rare and the last thing to suspect once everything else checks out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Check the oxygen sensor heater fuse first. It's the fastest win and a blown fuse can knock out more than one sensor at once
- 2. Read the codes properly and note anything alongside P0057. A pattern of heater faults across several sensors points at a fuse or relay rather than one duff sensor
- 3. Inspect the bank 2 sensor 2 connector for corrosion, melted plastic or a loose latch. Unplug it and look at the pins, water damage is obvious once it's open
- 4. With ignition on, back-probe the heater supply at the connector. You want to see around 12V on the feed side
- 5. Measure the heater element resistance across the two heater pins. Expect roughly 2 to 5 ohms cold. Infinite reading means the element is open and the sensor is done
- 6. If the sensor and supply both check out, test continuity on the control wire back to the ECM for an open or high resistance before condemning the module
Common questions about P0057
Do I have to buy a genuine sensor or will a cheaper one do? +
For a rear monitoring sensor like this, a quality branded aftermarket unit from Bosch, NTK or Denso is fine and costs a fair bit less than main dealer parts, somewhere around £30 to £80 depending on the car. What you want to avoid is the no-name eBay specials, the heater elements in those are hit and miss and you can end up with the same code a fortnight later. Match the part number to your exact engine, fitment varies even within the same model range.
Is it alright to keep driving like this? +
Yes, you can drive on it for now without any drama. The car won't go into limp mode and it'll start and run normally. You just lose a little efficiency from cold and your emissions will be slightly higher until the sensor heats up the slow way. Don't leave it for months though, get it looked at when it's convenient rather than ignoring the light forever.
Will this fail my MOT? +
The code on its own won't fail you, but the warning light will. MOT testers check that the engine management light goes out as it should, and a lit MIL is a fail under the current rules. If the underlying fault means your emissions are out, the gas test could fail too. Fix the cause, clear the light, then drive a few miles so the readiness monitors reset before you book the test.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →