The oxygen sensor before the catalytic converter on bank 1 (sensor 1) is the main control sensor for the mixture. It is either a switching sensor (about 0.1 V lean to 0.9 V rich) or a wide-band sensor that works with a pump current evaluated by an interface chip. P0134 means the sensor delivers no moving signal, typically because the circuit is open or the cell is cold or dead. The control module feeds a bias voltage, and that is all it sees: GM fails a signal stuck at 350–550 mV (or above 1700 mV with a 1.9 V bias) after warm-up, within about 15 s, or a cell resistance above 20 kΩ in hot exhaust; two trips. Subaru's wide-band sensor fails above 500 Ω cell impedance with immediate MIL. Ford's Bosch wide-band systems have used P2237 for this since 2011. A stored code usually switches mixture control to open loop and suspends adaptation and converter monitoring.
Medium severity. Can I keep driving?You can reach a repair shop, but the engine will run without fine mixture control: it will use more fuel and can damage the catalytic converter over time. Do not take long trips, and stop driving if hard jerking or a strong exhaust smell appears.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank. Sensor 1 is the oxygen sensor before the catalytic converter.
Symptoms
- Check engine light on
- No mixture control (open loop), higher consumption
- Higher emissions, possible emissions test failure
Most likely causes
- Open or high-resistance signal or ground wire, connector loose or corroded
- Sensor faulty (cell high-resistance, worn out)
- Sensor heater faulty – sensor does not get hot enough
- Exhaust leak ahead of the sensor or cracked sensor
- Control module bias or measuring circuit faulty
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P0134 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 1: Air and fuel
- 34: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0134?
You can reach a repair shop, but the engine will run without fine mixture control: it will use more fuel and can damage the catalytic converter over time. Do not take long trips, and stop driving if hard jerking or a strong exhaust smell appears.
What causes code P0134?
The most common causes are: open or high-resistance signal or ground wire, connector loose or corroded; sensor faulty (cell high-resistance, worn out); sensor heater faulty – sensor does not get hot enough.
Related codes
- P0133O2 Sensor Circuit Slow Response Bank 1 Sensor 1
- P0135O2 Sensor Heater Circuit Bank 1 Sensor 1
- P0131O2 Sensor Circuit Low Voltage Bank 1 Sensor 1
- P0132O2 Sensor Circuit High Voltage Bank 1 Sensor 1
- P0154O2 Sensor Circuit No Activity Detected Bank 2 Sensor 1
- P2237O2 Sensor Positive Current Control Circuit/Open (Bank 1 Sensor 1)
Sources
- law.cornell.edu: 13 CCR 1968.2
- gsi.ext.gm.com: 18OBDG03A Engine Diagnostics
- saabwisonline.com: dtc p0134 p0140 p0154 or p0160 lf1 lfw
- saabwisonline.com: dtc p0134 o2 sensor circuit no activity detected b
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.