P0051: HO2S Heater Control Circuit Low (Bank 2 Sensor 1)
Quick Answer
Safe to drive (short-term)
P0051 means the engine computer sees too little current in the heater of the front oxygen sensor on bank 2, the side of a V or flat engine that does not hold cylinder 1. Only engines with two cylinder banks can set it. The heater brings the sensor to working temperature quickly after a cold start, and without it the mixture runs on fixed values for longer. The usual causes are a burned-out heater, an open wire, or a failed sensor relay or fuse. A new front sensor on this bank typically costs 130 to 400 EUR fitted.
- Severity
- Low · Emissions
- Estimated repair cost
- From €1 to €400+, varies by vehicle
€1 or €400, depending on your car.
- Replace sensor heater fuse€1–€3
- Replace front air-fuel or oxygen sensor (Bank 2)€130–€400
A scan shows whether P0051 is really stored on your car, which codes sit next to it and how urgent each one is.
A scan needs a Bluetooth OBD2 adapter (Bluetooth LE on iPhone), about €25-60; the built-in demo runs without one. See which adapter to buy
What does P0051 mean?
P0051 is a emissions-related diagnostic trouble code classified as low severity.
What are the symptoms of P0051?
- Check engine light on, usually with no change in how the car drives
- Bank 2 stays on fixed (open loop) mixture values for longer after a cold start
- Slightly higher fuel use on short trips and cold mornings
- Oxygen sensor heater readiness monitor stays not ready after the code is cleared
- Possible emissions test failure while the light is on
- Other sensor heater codes at the same time when a shared fuse or relay has failed
What causes P0051?
Open or burned-out heater element inside the bank 2 front sensor, from age, heat cycles and mileage
: high
Open circuit or chafed wire between the sensor connector and the engine computer, often where the harness runs near the hot exhaust
: medium
Blown fuse or failed relay in the supply to the front sensor heaters
: medium
Corroded, loose or heat-damaged connector at the sensor
: medium
Missing or poor ground at the engine computer for the heater driver circuit
: low
Faulty heater driver inside the engine computer (only after the sensor, wiring, relay and grounds have all tested good)
: low
Is it safe to drive with P0051?
Generally yes, for short-term driving. Safe to drive for now. The engine still runs, but the bank 2 side stays on fixed mixture values for longer after a cold start, so fuel use and exhaust emissions rise a little. The warning light also hides any new fault and can fail an emissions test, so have the circuit checked within a few weeks.
How do you diagnose P0051?
- Confirm which side is bank 2. It is the cylinder bank that does not contain cylinder 1, so the owner's manual or an engine diagram decides it, not left or right. Check that the code is not stored together with a bank 1 heater code, which would point to a shared fuse or relay
- Find the sensor heater fuse and relay in the fuse box diagram and test them. A fuse that keeps blowing means a short in the heater or its wire
- Unplug the bank 2 front sensor and measure the resistance across the two heater pins against the maker's value. One Toyota procedure for a V6 gives 1.8 to 3.4 ohms; other makes differ, so use your car's figure. An open circuit means the heater has failed
- With the key on, check for supply voltage on the heater power pin of the harness plug. No voltage points to the fuse, relay or supply wire
- Check continuity of the heater control wire from the sensor plug to the engine computer, and look for chafing, melted insulation or pins pushed back in the connector
- If sensor and wiring test good, check every ground that serves the engine computer before condemning it. In a published case on a Lexus ES 350 V6, P0051 survived two new sensors and three replacement computers until a missing ground at the engine computer was found
- After the repair, clear the code, do a cold start and a normal drive, and use a generic reader to confirm the heater monitor completes and the fuel system reaches closed loop
How much does P0051 cost to fix?
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Replace sensor heater fuse | €1–€3 | €0–€0 | €1–€3 | Easy |
| Replace sensor heater relay | €10–€40 | €20–€60 | €30–€100 | Easy |
| Repair wiring or connector | €5–€20 | €40–€120 | €45–€140 | Moderate |
| Replace front air-fuel or oxygen sensor (Bank 2) | €80–€300 | €50–€100 | €130–€400 | Moderate |
| Workshop circuit diagnosis (power, ground and heater current) | €0–€0 | €60–€120 | €60–€120 | Professional |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
P0051 on specific vehicles
P0051 on Lexus
Lexus ES 350 (3.5 V6)
P0051 on Nissan
Nissan 350Z (VQ35HR V6)
Related diagnostic codes
Common questions about P0051
- What does P0051 mean?
- P0051 is a heater control circuit fault on the front oxygen sensor (sensor 1) of bank 2. The engine computer expects a set amount of current through the heater and sees too little. Bank 2 is the cylinder bank without cylinder 1, so only V6, V8 and flat engines can show it.
- Is P0051 the same on every make?
- The wording is generic, but makers describe it differently. Nissan lists it as the air-fuel ratio sensor 1 heater control circuit low input on the 350Z, and Toyota sets it on its Lexus V6 when heater current drops under 0.8 A. The check is similar everywhere: fuse and relay, supply voltage, heater resistance, then the control wire and grounds.
- Can I drive with a P0051 code?
- Yes, for a short time. The engine is not at risk, but bank 2 spends longer on fixed mixture values after a cold start, which costs a little fuel and adds emissions. Repair it within a few weeks, because the light hides new faults and an emissions test will fail with it on.
- How do I know whether it is bank 1 or bank 2?
- Bank 1 is the side with cylinder 1, bank 2 the other side. On a transverse V6 the two banks can be front and back rather than left and right, so look up your engine instead of guessing. A generic reader shows the bank in the code itself: P0051 is always bank 2.
- Will a new sensor fix P0051?
- Often, because a burned-out heater is the most common cause, but not always. If the heater resistance and supply voltage test good, the fault is in the wire, a ground or the engine computer, and a new sensor will not clear the code.
- How much does it cost to fix P0051?
- A fuse costs 1 to 3 EUR and a relay about 30 to 100 EUR fitted. A wiring repair is roughly 45 to 140 EUR. A new front sensor on bank 2 costs about 130 to 400 EUR fitted, and a workshop diagnosis of the circuit about 60 to 120 EUR.
Read our detailed guides
Sources
- automotivetechinfo.com automotivetechinfo.com/2021/12/the-sad-saga-of-the-2007-lexus-es350-and-a-p0051-
- en.wikipedia.org en.wikipedia.org/wiki/Lexus_ES
- 350z.se 350z.se/fsm/coupe/2007/ec.pdf
- en.wikipedia.org en.wikipedia.org/wiki/Nissan_350Z