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P0429 OBD-II Trouble Code: Catalyst Heater Control Circuit

Check Engine Light

P0429 code definition

The P0429 code pertains to improper operation of your heated oxygen sensors. It signifies that both sensors have malfunctioned in some way.

What the P0429 code means

Your vehicle’s ECM (Engine Control Module) tracks the switching frequency ratio of the dual heated oxygen sensors. There are oxygen sensors one, which are your front O2 sensors, and heated oxygen sensors 2, which are the O2 sensors to your rear. When your vehicle is operating correctly, these two sensors work in tandem.

A catalyst converter with a high capacity for oxygen storage will indicate when there is a low switching frequency of the rear O2 sensor (heated oxygen sensor 2). As the storage capacity for oxygen decreases, that rear sensor’s switching frequency will do the opposite (it goes up) As it increases in capacity, it and the other oxygen sensor may eventually reach a predetermined limit value. When that happens, a malfunction in the catalyst is diagnosed and the P0429 code is stored by your ECM.

What causes the P0429 code?

There are three main culprits that may be responsible for P0429:

  • The catalyst temperature sensor harness is either shorted or completely open
  • The catalyst temperature sensor circuit is suffering from a poor connection
  • The catalyst temperature sensor has become faulty

What are the symptoms of the P0429 code?

Usually, the Check Engine light should come on, letting you know something is wrong. Depending on the fallout from this problem, your ECM may actually detect the O2 sensor heater circuit is low and activate failsafe mode. If this happens, you’ll need to turn the ignition off. Failsafe mode won’t go away until the original problem is addressed.

You may also notice that your vehicle runs a bit rough or even has a hard time accelerating.

How does a mechanic diagnose the P0429 code?

To diagnose this problem, your mechanic will need to use an OBD-II scanner. Usually, they’ll initiate a reset and then take the vehicle out on a test drive to see if the code reappears. If that happens, the mechanic will proceed to checking the power and ground to the sensor. This will include a complete examination of the wiring and sensor. Due to the extreme heat of the catalytic converter and exhaust, it is very important to check all the wiring.

Common mistakes when diagnosing the P0429 code

As we just mentioned, the wiring often gets damaged because of how hot it is next to these components, so it’s very likely that a simple repair can clear P0429 for good. This makes it all the more unfortunate when mechanics don’t do a thorough inspection and simply move onto expensive/unnecessary repairs.

How serious is the P0429 code?

Though it’s not going to put your life at risk, this type of problem is extremely frustrating as it can greatly hinder the performance of your car and even force you to spend more at the pump.

What repairs can fix the P0429 code?

Your mechanic will most likely do one of the following to attack this problem.

Additional comments for consideration regarding the P0429 code

It’s not unheard of for code P0429 to be accompanied by a number of others. If that’s the case for your vehicle, it would be wise to address those other codes first and then deal with this one. That will often do the trick or at least make it much clearer what has to happen to repair code P0429.

Need help with a P0429 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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