P0138
O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
The computer is seeing too much voltage from the downstream oxygen sensor on bank 1. This usually means the sensor is faulty, the wiring is damaged, or the exhaust has an issue affecting the reading.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20–$120
- SHOP
- $150–$450
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Faulty downstream oxygen sensor (Bank 1 Sensor 2)
- Damaged, corroded, or contaminated wiring or connector for the sensor
- Exhaust leak near the sensor or damaged exhaust components
Typical repair cost
DIY usually runs $20–$120. Typical shop repair lands around $150–$450, depending on the root cause.
01 / Definition
P0138 means the powertrain control module has detected a high-voltage condition in the Bank 1 Sensor 2 oxygen sensor circuit. Bank 1 Sensor 2 is the downstream O2 sensor, located after the catalytic converter on the side of the engine with cylinder 1. The code can be set by a failed sensor, wiring short to voltage, connector problems, or a catalytic converter or exhaust condition that affects sensor readings.
02 / Drive status
With caution. The vehicle will often still run, but fuel economy and emissions can be affected. If the check engine light is flashing, the car runs poorly, or you smell fuel, stop driving and diagnose it right away.
03 / Symptoms
- Check engine light on
- Poor fuel economy
- Failed emissions test
- Rough running in some cases
- Fuel smell in some cases
- Other oxygen sensor or catalyst codes may appear
04 / Causes
| 1 | Faulty downstream oxygen sensor (Bank 1 Sensor 2) | high |
|---|---|---|
| 2 | Damaged, corroded, or contaminated wiring or connector for the sensor | high |
| 3 | Exhaust leak near the sensor or damaged exhaust components | medium |
| 4 | Short to voltage in the O2 sensor signal circuit | medium |
| 5 | Rich-running engine condition causing abnormal sensor readings | medium |
| 6 | Failed catalytic converter affecting downstream sensor behavior | low |
| 7 | PCM issue or software problem | low |
05 / Diagnostic sequence
- 01Scan for all stored and pending codes and freeze-frame data.
- 02Inspect Bank 1 Sensor 2 wiring, connector, and harness for heat damage, corrosion, looseness, or broken wires.
- 03Check for exhaust leaks near the rear oxygen sensor and catalytic converter.
- 04Look at live data from Bank 1 Sensor 2 and compare it to Bank 1 Sensor 1 and fuel trim data.
- 05Test the sensor circuit for proper voltage, ground, and signal response according to the vehicle service information.
- 06Check for rich engine conditions or related codes such as misfire, fuel trim, or catalyst codes.
- 07Replace the sensor if wiring and exhaust are okay and the sensor signal is clearly incorrect.
- 08Clear codes and road test to confirm the repair.
06 / Repairs
| 1 | Repair damaged wiring, connectors, or terminals in the Bank 1 Sensor 2 circuit | $20–$150 |
|---|---|---|
| 2 | Replace the downstream oxygen sensor on Bank 1 | $50–$250 |
| 3 | Repair exhaust leaks or damaged exhaust components near the sensor | $50–$400 |
| 4 | Fix engine rich-running issues, misfires, or fuel system problems if present | $100–$600 |
| 5 | Replace the catalytic converter if testing confirms it is causing the fault | $500–$2,000+ |
MFG / Manufacturer notes
These supplements add make-specific diagnostic framing. Pages without full matrix backing or lane approval stay guarded and canonicalize back here until they are explicitly approved for indexing.
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Dodge P0138
Expansion-candidate noindex child page
07 / Related codes
08 / FAQ
Is P0138 an upstream or downstream oxygen sensor code?
It is a downstream code. Bank 1 Sensor 2 is the oxygen sensor after the catalytic converter.
Can a bad catalytic converter cause P0138?
Yes, but it is less common than a bad sensor or wiring problem. The converter should be tested before replacement.
Will replacing the oxygen sensor always fix P0138?
No. Wiring damage, connector problems, exhaust leaks, and engine running issues can also cause the code.
Can I drive with P0138?
Usually yes for short trips, but it should be diagnosed soon because fuel economy and emissions can be affected.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.