P0050
PowertrainHO2S Heater Control Circuit (Bank 2 Sensor 1)
For most people the first sign is just the engine light coming on, maybe with a slight dip in fuel economy that you'd struggle to spot unless you watch the gauge. Underneath that, the ECU has found a fault in the heater circuit of the front oxygen sensor on bank 2, which is the cylinder bank on the opposite side from cylinder number 1. That little heater is there to bring the sensor up to working temperature fast on a cold start so the engine can run closed-loop sooner. When the heater stops drawing the right current, or the circuit feeding it goes open or short, P0050 lands.
ⓘ Information only. This page provides general educational information about fault code P0050. 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 P0050 mean?
P0050 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: HO2S Heater Control Circuit (Bank 2 Sensor 1).
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, usually with nothing else obvious to feel
- • Slightly worse fuel economy, most noticeable on short cold-start trips around town
- • A bit of a rough or hunting idle on some cars while the engine is still cold
- • Higher tailpipe emissions, which can show up at the MOT smoke test
- • Engine takes longer than normal to settle into smooth running from cold
Possible causes
Causes commonly associated with P0050, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. The heater element inside the sensor has failed, by far the most common cause on higher-mileage cars as the element simply burns out over time
- 2. Corroded or damaged wiring at the connector plug near the sensor, often from heat and road salt down by the exhaust
- 3. A blown fuse feeding the heater circuit, sometimes shared with the other sensor so check what else dropped out
- 4. Poor earth or a loose pin in the connector giving an intermittent fault that comes and goes with temperature
- 5. A chafed or shorted wire in the loom where it runs close to hot exhaust or a moving part
- 6. A failed ECM, but this is rare and you'd only suspect it after 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. Pull the codes and look at live data first. If bank 1 sensor 1 (often paired with P0030) is fine and only bank 2 is faulting, you've already narrowed it to one sensor and its wiring
- 2. With the ignition on, back-probe the connector at the bank 2 front sensor and check you've got around 12V on the heater supply wire. No voltage points at the fuse or wiring rather than the sensor
- 3. Check the relevant fuse. On a lot of cars one fuse feeds both front sensor heaters, so a blown fuse will usually throw P0030 as well as P0050
- 4. Unplug the sensor and measure the resistance across the two heater pins with a multimeter. A healthy heater is typically a few ohms, often around 4 to 10 depending on the sensor. Open circuit or wildly high means the element is dead
- 5. Inspect the connector and the loom back from the sensor for green corrosion, melted insulation, or a wire that's been resting on the exhaust
- 6. Clear the code and drive a few cold-start cycles to see if it returns, which helps catch the intermittent wiring faults
Common questions about P0050
Will this stop my car passing its MOT? +
The code on its own isn't a tick-box failure, but if the engine warning light is glowing when the tester looks at the dash, that's an automatic fail under the current MOT rules. On top of that, a dead sensor heater can knock the emissions readings out enough to fail the gas test on a petrol car, because the engine stays in open-loop and runs richer than it should from cold. Sort the fault and drive enough cycles to clear the light before you book the test.
What am I likely to pay to get it sorted? +
If it turns out to be a blown fuse or a tidy wiring repair, you might be looking at £40 to £90 at an independent garage. A new front oxygen sensor for bank 2 is commonly £40 to £150 for the part, and fitted at a good independent you'd usually be in the £100 to £250 range all in depending on how buried the sensor is. A main dealer using a genuine sensor can push that towards £300 or more, mostly on the part price and their labour rate. Get the access checked first, because a sensor tucked up behind the manifold takes a lot longer than one hanging in clear air.
How do I know if it's the sensor or just the wiring? +
Two quick checks split it. First, measure the heater resistance across the sensor's two heater pins with the plug off. If it reads open circuit or way too high, the element inside is gone and the sensor is your fix. If it reads a few ohms like it should, the sensor heater is fine and the fault is upstream. Second, check for 12V on the supply side of the connector with the ignition on. No voltage there with a healthy fuse means a broken or corroded wire or earth between the relay and the plug. Combining those two tells you which way to spend your money before you buy anything.
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 →