P0050 Code: O2 Sensor Heater Control Circuit (Bank 2 Sensor 1)
The heater circuit of the upstream sensor on bank 2 – the side without cylinder 1 – is out of range.
At a glance
Severity: Low
- Meaning
- O2 Sensor Heater Control Circuit (Bank 2 Sensor 1)
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $0–$1,200
- DIY difficulty
- Moderate
Bank 2 only exists on engines whose exhaust is split into two sides: V6, V8 and flat engines, plus some inline sixes with two separate exhaust manifolds, such as several BMW six-cylinders. P0050 concerns the heater of the first sensor on that second side, the one ahead of its catalytic converter. The engine computer regulates this heater and cross-checks voltage or current, and P0050 is the general result when the feedback doesn't fit the command but is neither a clear open nor a clear short. The practical advantage on a two-bank engine is that bank 1 has a twin sensor to compare against: same part, same heater, same kind of circuit. Comparing the two quickly separates a failing sensor from a supply problem.
Can I keep driving? No harm in driving it. Bank 2 runs without mixture feedback for longer after each cold start, so fuel use rises a little; fix it before your next emissions test.
How to read P0050
- P Powertrain
- 0 Generic (SAE)
- 0 Fuel/air & emissions (aux.)
- 50 Specific fault
Symptoms
- Check engine light with only the bank 2 heater flagged, bank 1 normal
- Bank 2 fuel trims sit at 0 % while bank 1 trims are already moving after a cold start
- Bank 2 upstream sensor becomes active much later than its bank 1 twin
- Code sets on some cold starts but not others
- Engine drives normally
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Bank 2 upstream sensor heater aging or intermittently open
- Connector on the hard-to-reach side corroded or not fully seated
- Harness baked by heat soak from the rear exhaust manifold near the firewall
- Sensor for the other bank fitted, so the pigtail is stretched or the connector strained
- Poor contact at a separate bank 2 heater fuse or relay
- Heater driver in the engine computer
Diagnosis step by step
Work out which side is bank 2
Bank 1 is always the side with cylinder 1. On Toyota's transverse 3.5-liter V6, for example, bank 1 is the rear bank and bank 2 faces the radiator. On GM and Chrysler rear-drive V8s bank 2 is the passenger side, while Ford V8s put bank 2 on the driver's side. Confirm in service information before buying a sensor.
Tools: Flashlight
Compare both banks in live data
Start the engine fully cold and watch both upstream sensors and both sets of fuel trims. Bank 1 should go active and start trimming within a minute or so; if bank 2 lags far behind or never goes active, its heater really isn't doing its job.
Tools: OBD-II scanner
Measure both heaters and compare
With the engine cold, measure heater resistance at both upstream sensor connectors. Sensors with the same part number should read within about an ohm of each other. A bank 2 reading that is much higher, unstable or open confirms the sensor.
Tools: Multimeter
Check the bank 2 feed under load
If bank 1's heater works and both share a fuse, the fuse itself is fine and the problem is in the bank 2 branch. Back-probe the bank 2 feed with the sensor connected and engine idling cold; it should be within about half a volt of battery voltage.
Tools: Multimeter
Plan the access
A bank 2 sensor on the firewall side can mean removing the upper intake plenum or cowl panel, or working from underneath with a long extension and a slotted O2 sensor socket. Soaking the threads with penetrating oil ahead of time makes a big difference on a sensor that has seen many heat cycles.
Tools: O2 sensor socket, Torque wrench
Verify both banks match
After the repair, cold-start the engine and confirm both banks enter closed loop at about the same time and the heater monitor completes. A clean match between the banks is the best proof the fault is gone.
Tools: OBD-II scanner
Where the parts are
- 1Upstream O2 sensor
- 2Catalytic converter
- 3Downstream O2 sensor
- 4Diesel particulate filter
- 5Turbocharger
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean and reseat the bank 2 sensor connector | Yes | $0–$60 |
| Bank 2 upstream sensor, part only | Yes | $80–$270 |
| Bank 2 upstream sensor replaced at a shop, including access work | No | $250–$600 |
| Repair heat-damaged harness near the firewall | No | $120–$350 |
| Engine computer heater driver repair | No | $300–$1,200 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
A stored P0050 with the check engine light on fails an OBD-II emissions inspection. Bank 2's oxygen sensor monitors also have to complete, so plan for several cold starts and normal driving after the repair.
Frequently asked questions
Which side of my engine is bank 2?
The side that doesn't contain cylinder 1. That varies by manufacturer and even by engine family, so always check a diagram for your engine. Replacing the sensor on the wrong bank is one of the most common and expensive mistakes with this code.
Should I replace both upstream sensors while I'm at it?
It isn't required. If both are original on a high-mileage engine and the labor to reach them overlaps, doing both at once can save a second visit, but a healthy bank 1 sensor will keep working fine on its own.
Can a four-cylinder set P0050?
Normally no: inline four-cylinders have only bank 1. If a scan tool shows P0050 on a four-cylinder, confirm the engine variant and read the codes with a second tool before chasing a part that doesn't exist.
How does P0050 relate to P0155?
They describe the same heater on the same bank 2 upstream sensor. P0155 is the older definition; newer software uses P0050, P0051 and P0052 to separate a general fault from an open or a short.