P0134

O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)

Car Fault Codes Emissions & exhaust

Can you still drive? Yes, normally

Who can fix it? DIY with some experience

Typical repair time 30 minutes – 2 hours

Typical cost SAR 100 to 900

What it means

The engine computer has found that the upstream oxygen sensor signal on bank 1 stays flat after the engine warms up, as if no sensor were connected. This is usually caused by an open signal wire, a sensor that is not being heated, or a completely dead sensor, so the computer falls back to estimated fuel control.

Symptoms4

Check engine light on.
Higher fuel consumption.
A sensor heater code may appear with it.
Failed emissions test.

Possible causes5

Open signal wire or unplugged connector.
Faulty sensor heater or heater supply circuit, so the sensor never reaches working temperature.
Completely failed sensor.
Corroded terminals inside the connector.
Engine computer fault (rare).

How to diagnose5

First check for heater codes such as P0135 or P0030, and fix them before anything else.
Watch the signal after warm-up; if it stays fixed at the reference voltage the computer supplies, the sensor is dead or its circuit is open.
Check that the connector is fully seated and free of corrosion.
Check continuity of the signal and ground wires between the sensor and computer using the manufacturer wiring diagram.
If the circuit is sound, replace the sensor.

How to fix5

Reconnect or clean the connector.
Repair the broken wire and route it away from the exhaust.
Repair the heater circuit or its fuse if it is faulty.
Replace the upstream oxygen sensor if it is proven to give no signal.
Clear the codes and confirm the signal starts switching once the engine is warm.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

An unplugged connector or broken wire costs little, while replacing the sensor reaches the upper end of the range.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

Why does P0134 often appear with a heater code?

Because the sensor gives no useful signal while cold, so if its heater fails the signal can stay flat and the computer reports no activity.

How is this different from low voltage P0131?

In P0131 the signal is low; here it is flat and not moving, which points more to an open circuit or an unheated sensor.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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