Code result
P0140
O2 Sensor Circuit No Activity Detected
Moderate severity
What it means
The ECU detects no switching or excessively slow response from the downstream oxygen sensor on bank 1. Typical for an aged or poisoned sensor; downstream sensors should show a relatively flat signal but must respond to fueling changes during diagnostic monitor runs.
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
Sensor aged or poisoned
highOne of the most commonly reported causes for this code — check this first.
Sensor heater circuit weak
mediumA plausible cause — test and verify before replacing parts.
Catalytic converter so degraded that downstream signal mirrors upstream
lowLess common, but worth ruling out after the more likely causes.
Related help
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