Mazda CX-9 P0134: O2 Sensor → No Activity Detected B1S1

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P0134 Mazda CX-9

P0134 is a relatively common OBDII trouble code. It’s generic, which means that it has the same meaning for any vehicle with OBDII.

It means that the PCM/ECM is not detecting any activity from the sensor.

 

P0134 Definition

P0134: O2 Sensor → No Activity Detected →Bank 1 Sensor 1

The CX-9’s computer uses the oxygen sensor to measure the amount of O2 gases in the exhaust. It uses this data to tune the engine on the fly.

When there is no signal from this oxygen sensor, the engine will not be able to run at optimal efficiency, and you’ll get that annoying check engine light.

Mazda CX-9 P0134 Diagnose

P0134 affects Bank 1 Sensor 1. Bank 1 is the side of the engine that has the first piston in the firing order. That means that different model years and engine can have Bank 1on a different side.

Look up which side of the engine bank 1 is on

If it’s an inline engine (almost all 4 cylinder motors), you don’t need to worry about which side it’s on, since there’s only one exhaust manifold. Sensor 1 will be the first sensor in the line.

The PCM supplies a voltage or roughly 450mv to the O2 sensor. As the engine warms up, this voltage is supposed to change. If it doesn’t (or does so too slowly) the P0134 code will be thrown.

This video is extremely helpful in going about how to test P0134:

 

P0134 Symptoms Mazda CX-9

Most of the time, the only symptom of P0134 is going to be the service engine soon light. But, there can be other symptoms. These include:

  • Decreased fuel mileage
  • Stalling engine
  • Increased exhaust smell, black color from tail pipe
  • Misfire

 

Mazda CX-9 P0134 Causes

There are a lot of different things that can cause P0134 to be thrown in the CX-9. Here is a list of common potential causes for P0134 in general:

  • Wiring– Most of the time, Bank 1 Sensor 1 is not going to be very difficult to get to. You’ll want to visually inspect the harness where it plugs into the O2 sensor. Make sure that the pins look good and that the harness is seating well and not cracked. Also check to make sure that the wiring is not frayed or shorted. How to check for a short (YouTube).
  • Bad O2 Sensor– The oxygen sensor itself can go bad. This is often the cause of P0134. Replacing it without testing the wiring going to/from it first is a gamble that will often pay off, but it’s still a good idea to check your harness connections and inspect it first.
  • Exhaust Leak– An exhaust will can cause P0134. You should be able to listen and find it.
  • Intake Leak– If there is a leak in the intake manifold, it can cause the P0134. Often, when an intake leaks, it’ll affect the vehicles ability to idle properly. How to test an intake manifold (knowyourparts.com)
  • Coolant Temp Sensor– A bad coolant temperature sensor will cause P0134. By giving the engine’s computer the wrong info about how warm it is, it can throw the feedback loop of between the it and the sensor.
  • Bad Heater Circuit Fuse

 

Conclusion

There are a lot of issues that can cause P0134 in the Mazda CX-9. Most of the time, it’ll be the O2 sensor or the wiring to it. If you feel there is anything that you could do to improve or add to this article, please leave a comment below.