P0138 — O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
Category: Powertrain Severity: Low
Updated:
DTC code P0138 means: O2 Sensor Circuit High Voltage (Bank 1 Sensor 2). It falls under the "Powertrain" category, with an estimated severity of Low. Common causes include failed downstream O2 sensor, short between signal and heater and rich mixture; it's worth confirming the diagnosis before replacing parts.
Possible causes
- Failed downstream O2 sensor
- Short between signal and heater
- Rich mixture
- Sensor contamination
Symptoms
- Check engine light
- Usually no symptoms
How to diagnose it step by step
- Read sensor 2 voltage.
- Check fuel trims.
- Check the wiring.
- Replace the sensor.
How to fix it
If the downstream sensor reads above 1 V continuously, it is almost always failed or shorted to the heater. Replace it.
Estimated repair cost
$100–280.
Frequently asked questions
What does DTC code P0138 mean?
O2 Sensor Circuit High Voltage (Bank 1 Sensor 2).
Is code P0138 serious?
Severity Low. Usually a minor fault; check the causes listed.
Can I keep driving with code P0138?
Yes, it is safe to drive.
Related codes
P0137 P0139 P0136 P0135 P0134 P0133 P0132 P0131 P0130 P0140
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