Code result
P0138
O2 Sensor Circuit High Voltage
Moderate severity
What it means
The downstream oxygen sensor signal is fixed at a high voltage, indicating either a continuously rich downstream reading (less common, since post-cat exhaust should be more stable) or a short to supply voltage in the signal circuit.
Is it safe to drive?
Use caution
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.
Most likely causes
Signal wire shorted to supply voltage
highOne of the most commonly reported causes for this code — check this first.
Downstream sensor failed
mediumA plausible cause — test and verify before replacing parts.
Connector pins corroded - high contact resistance
lowLess common, but worth ruling out after the more likely causes.
Related help
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