P0134 — O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 1)
Low severityWhat it means
P0134 is stored when the engine control unit sees a fault involving the upstream oxygen sensor on bank 1 (sensor 1). The bank 1 upstream oxygen sensor measures exhaust oxygen before the catalytic converter and is the main input the control unit uses to trim fuel. “No activity” means the oxygen-sensor signal is flatlined, so the control unit cannot use it for fuel control at all.
Common symptoms
- A signal that stays flat instead of switching
- Rough running or higher fuel use
- Check engine light
- Failed emissions test
Likely causes
- Dead sensor or failed heater element
- Open wiring or lost power/ground to the sensor
- Aged or contaminated oxygen sensor
- An exhaust leak near the sensor
What to check first
- Check sensor heater power and ground, then the signal wiring
- Watch the upstream sensor switch between rich and lean in live data
- Inspect for exhaust leaks and check the sensor wiring
Can you keep driving?
Drivable short-term; a fuel-control sensor fault wastes fuel and can affect the catalytic converter, so repair soon.
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