P0138

O2 Sensor Circuit High Voltage Bank 1 Sensor 2

Fuel & air metering (O2 sensor) Generic OBD-II Medium

What it means

P0138 means the downstream oxygen sensor on bank 1 (after the catalytic converter) is reporting an abnormally high voltage — a rich signal. Because this sensor checks the converter rather than controlling fuel, the engine drives normally. It usually points to a failed sensor, a wiring short to voltage, or a genuine rich condition.

Medium

Can I keep driving? Yes — this is the downstream (post-catalyst) oxygen sensor, so the car drives normally; it mainly affects emissions monitoring, but get it checked so a real fuel or exhaust problem isn't hidden.

Real-world scan data

Seen in

2,466

scans in the past year

Found in

0.4%

of scans

0.7%

of scans that found faults

Appears alongside · share of P0138 scans

P0141in 22.1% of scans

P0136in 20.2% of scans

P0300in 18.8% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on (often the only symptom)
Slightly worse fuel economy in some cases
Fails an emissions test

Common causes

Most likely first

Failed downstream oxygen sensorLikely
Wiring or connector shorted to voltage, or a poor connectionCommon
Exhaust leak near the sensorCommon
Engine actually running rich (fuel-trim or injector issue)Less often

How to diagnose & fix

Work through it in order

Read freeze-frame and live O2 data to see if the voltage is truly stuck high.
Inspect the sensor's wiring and connector for damage, corrosion, or a short to power.
Check for exhaust leaks near the sensor.
Rule out a rich-running condition before condemning the sensor.
Replace the downstream O2 sensor if it tests faulty. Clear and re-test.

FAQ

Quick answers

Is it safe to drive with P0138?+

Yes. Bank 1 Sensor 2 is after the catalytic converter and doesn't control fueling, so drivability is normal. Still, fix it so the emissions system can monitor properly.

Can I just clear P0138?+

It returns unless the sensor, wiring, or rich condition is fixed. Clearing only helps confirm whether the fault is current or was a one-time glitch.

Read & clear P0138 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX