Code result
P0137
O2 Sensor Circuit Low Voltage
Moderate severity
What it means
The downstream oxygen sensor signal is fixed at a low voltage. Either the catalyst is letting unburned oxygen through (sensor sees lean), the sensor itself is shorted to ground, or the catalyst is so degraded that the downstream signal mirrors a lean upstream condition.
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 ground
mediumA plausible cause — test and verify before replacing parts.
Catalyst degraded (often appears before P0420)
mediumA plausible cause — test and verify before replacing parts.
Exhaust leak between catalyst and downstream sensor
lowLess common, but worth ruling out after the more likely causes.
Related help
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