P0150 Code: O2 Sensor Circuit Malfunction (Bank 2 Sensor 1)
The upstream O2 sensor circuit on bank 2 is sending readings the ECU can't use, usually wiring or the sensor.
At a glance
Severity: Low
- Meaning
- O2 Sensor Circuit Malfunction (Bank 2 Sensor 1)
- System
- Fuel & Air Metering · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $60–$450
- DIY difficulty
- Moderate
P0150 is the general electrical fault code for the front oxygen sensor on bank 2, the cylinder bank that does not contain cylinder 1. The engine computer stores it when the signal from that sensor behaves in a way no working sensor could produce: voltage that drops out or spikes, an open circuit that comes and goes, or a reading that contradicts the internal reference the ECU applies to the wire. Unlike P0151 or P0152, which describe a signal that is stuck in one direction, P0150 almost always points to the wiring, the connector or the sensor body rather than to the fuel mixture. Only engines with two banks can set it: V6, V8 and V10 engines, boxer engines and a few straight-sixes with a split exhaust. The identical sensor on bank 1 gives you a built-in reference and, on many engines, a swap partner for testing.
Can I keep driving? You can keep driving. The ECU usually drops bank 2 into open-loop fueling, so mileage suffers a little, but nothing is being damaged. Don't leave it for months: a chafed harness that caused P0150 can short into neighbouring circuits later.
How to read P0150
- P Powertrain
- 0 Generic (SAE)
- 1 Fuel & air metering
- 50 Specific fault
Symptoms
- Check engine light on, sometimes only after the engine is fully warm
- Code sets and clears intermittently, often on rough roads
- Slightly higher fuel consumption, mostly noticeable on short trips
- Mildly uneven idle because bank 2 runs on default fueling
- O2 sensor monitor stays incomplete for the emissions test
- Occasional exhaust smell after a cold start
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Chafed, melted or broken wiring where the bank 2 sensor harness passes the exhaust manifold or heat shield
- Corroded, loose or water-filled connector at the bank 2 sensor 1 plug
- Internal failure of the sensor element (cracked ceramic, contaminated tip)
- Bank 1 and bank 2 sensor connectors swapped after intake or exhaust work
- Shorted heater wire bleeding voltage into the signal wire
- Universal replacement sensor spliced in wrong or with a poor joint
- Bad sensor ground or a fault on the ECU input
Diagnosis step by step
Locate bank 2 sensor 1 on your engine
Bank 2 is the side without cylinder 1: the driver side on Ford V8s, the passenger side on GM and Chrysler V8s, the driver side on Subaru boxers, and usually the front (radiator-side) bank on transverse V6 engines, though not on every make. Sensor 1 is the one screwed into the manifold or downpipe ahead of the converter.
Tools: Flashlight
Watch the signal pattern in live data
Graph bank 2 sensor 1 next to bank 1 sensor 1 on a warm engine at idle. A healthy narrowband sensor sweeps between roughly 0.1 and 0.9 V; sudden drops to 0 V, jumps to 5 V or a signal that freezes and resumes are electrical faults, not mixture problems. If the trace sits flat at about 0.45 V the whole time, the sensor never connected and P0154 describes the fault better.
Tools: OBD-II scanner
Wiggle-test the harness
With the engine idling and the graph running, flex the sensor pigtail, the harness section along the manifold and the connector itself. A flicker or dropout while you move a specific spot pinpoints the damage. Pay attention to where the harness crosses the heat shield and to any spot where it was tucked away during earlier repairs.
Tools: OBD-II scanner, Flashlight
Check the bias voltage at the harness connector
Unplug the sensor and, with the key on, measure the signal pin on the harness side against battery negative. Most manufacturers apply a bias of around 0.4 to 0.5 V; some use close to 0 V, so check the spec. A correct bias proves the wire back to the ECU is intact, then verify the sensor ground pin has good continuity to the engine block.
Tools: Multimeter
Inspect the connector halves
Look for green corrosion, pins pushed back into the housing and oil that has wicked up through the sensor's own wires. On front-bank sensors on transverse engines the plug sits in the splash from the fan and the wheel well; on rear-bank sensors it bakes near the firewall.
Tools: Flashlight
Swap the sensors between banks
If bank 1 and bank 2 use the same part, move the bank 2 sensor to bank 1 and vice versa, plugging each into its correct bank connector. If the code moves to P0130, the sensor is at fault; if P0150 stays, the problem is in the bank 2 wiring or the ECU input. Torque the sensors to spec, typically around 30 lb-ft.
Tools: O2 sensor socket, Torque wrench, OBD-II scanner
Repair properly and re-route
Repair damaged wires with heat-resistant wire and sealed joints, then secure the harness so it cannot touch the manifold again. A new sensor connected to a burnt harness will set P0150 again within days.
Tools: Pliers, Flashlight
Where the parts are
- 1Upstream O2 sensor
- 2Catalytic converter
- 3Downstream O2 sensor
- 4Diesel particulate filter
- 5Turbocharger
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Repair chafed or melted sensor wiring | No | $80–$250 |
| Replace bank 2 upstream O2 sensor yourself (part only) | Yes | $60–$250 |
| Replace bank 2 upstream O2 sensor at a shop | No | $180–$450 |
| Diagnostic time for an intermittent wiring fault | No | $100–$200 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Notes by brand
Ford
On Ford's modular and Coyote V8s bank 2 is the driver side. The bank 2 sensor 1 harness runs close to the steering shaft and the driver-side manifold heat shield, which is where chafing usually shows up.
Chevrolet
On GM small-block V8s cylinder 1 is on the driver side, so bank 2 is the passenger side. That harness passes the starter and the passenger-side manifold and is a common spot for heat damage.
Emissions / smog test impact
Will fail
A stored P0150 with the check engine light on fails an OBD-II smog or emissions inspection. After the repair, drive several warm-up cycles so the oxygen sensor monitor for bank 2 reports complete before you go to the test station.
Frequently asked questions
Which sensor is bank 2 sensor 1?
It's the oxygen sensor ahead of the catalytic converter on the cylinder bank that does not contain cylinder 1. A four-cylinder engine has no bank 2, so this code should only appear on V-type, boxer and some split-exhaust six-cylinder engines.
What's the difference between P0150 and P0130?
They describe the same fault on opposite sides of the engine: P0130 is the bank 1 upstream sensor, P0150 the bank 2 upstream sensor. If both are stored at the same time, look for something shared, such as a common ground, a fuse or an ECU problem, before replacing two sensors.
Does P0150 mean the sensor itself is bad?
Not necessarily. On bank 2 the wiring runs past a hot manifold and often through areas disturbed during other repairs, and a damaged harness or corroded connector sets exactly this code. Check the wiring and connector before you spend money on a sensor.
P0150 appeared right after intake manifold gasket work. Coincidence?
Probably not. On V6 and V8 engines the sensor connectors are unplugged or moved during that job, and the bank 1 and bank 2 plugs are often identical. A swapped or half-seated connector on the bank 2 side is the first thing to check.
Can I swap the bank 1 and bank 2 sensors to test?
Yes, if they are the same part number. Swap the sensors themselves, not just the plugs, and clear the code. If the fault follows the sensor to bank 1 as P0130, you've confirmed the sensor; if P0150 stays, the problem is on the bank 2 harness or ECU side.