Fault code P0429 – catalyst heater control circuit malfunction (Bank 1)

Fault code P0429 is called “Catalyst Heater Control Circuit Malfunction (Bank 1)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0429

This Diagnostic Trouble Code (DTC) is a generic code. Error P0429 is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

The catalytic converter is a part of the exhaust system that looks like a muffler. But its operation is very different from that of a muffler. The catalytic converter works by reducing exhaust emissions.

There is an oxygen sensor on the neutralizer in the front and rear. When the vehicle is warmed up and operating in closed circuit mode. The oxygen sensor O₂ reading in front of it should fluctuate. The reading of the oxygen sensor O₂ behind it should be fairly stable.

Normally, code P0429 is set and the check engine light (Check Engine) is illuminated if the readings of the two sensors reflect the same concentration of oxygen in the exhaust gases. This occurs when an electrical fault is detected in the heated catalytic converter control circuit. The error indicates that there has been a malfunction in the catalyst reading and it is not operating as efficiently as it should (according to specifications).

Nowadays, vehicles with emission control systems use heated oxygen sensors. The purpose of the heating element built into the oxygen sensor is to bring the sensor up to operating temperature faster.

Once this is done, the emission control will begin to work. The engine control module (ECM) monitors the temperature of the heated sensors. And if there is a malfunction, this code is set.

Symptoms of vehicle malfunctions

The main signal that an error P0429 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

1. The “Check engine” control lamp on the control panel will light up (the code will be stored as a fault).
2. Other related fault codes may also be present.
3. The engine stalls or starts poorly.
4. Floating revolutions, as well as attempts to stall at idle.
5. Decreased engine power.
6. Poor acceleration.
7. Increased fuel consumption.
8. Sometimes symptoms may be absent, despite the stored fault code.

This error is considered moderate if there are no symptoms. But if symptoms are present, the cause of the P0429 error should be corrected as soon as possible. Ignoring it may cause serious damage to the catalytic converter.

Factors that can cause this error code

The error code P0429 can mean that one or more of the following problems have occurred:

• Damaged or faulty oxygen sensor (O₂).
• Damaged or incorrectly connected oxygen sensor wiring (HO₂S).
• Damaged or leaking exhaust manifold, catalytic converter, muffler, exhaust pipe.
• Delayed ignition timing.
• Defective exhaust temperature sensor.
• Oxygen sensors on front and rear of catalytic converter are reporting too similar readings.
• Catalytic converter has failed.
• Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P0429

Some suggested steps for troubleshooting and fix the error code P0429:

1. Read all the error codes stored in the vehicle’s PCM memory with an OBD-II scan tool.
2. Check the operation of the oxygen sensor O₂ located behind the catalytic converter (at the exhaust outlet). Voltage reading of this sensor should be stable.
3. Diagnose other error codes that may have caused code P0429.
4. Troubleshoot the engine cylinder ignition timing and fuel system malfunctions.
5. Inspect the oxygen sensor installed behind the catalytic converter (at the exhaust outlet) for wear and damage.
6. Test-drive the vehicle to check the oxygen sensor.
7. Replace or reprogram faulty PCM if necessary.

Diagnose and repair of problems

If there are no additional errors, clear fault code P0429 and perform a short test drive. To allow the PCM to go into closed loop mode, then scan the system again and see if the code comes back.

Check the catalytic converter and leaks

Check for exhaust leaks, repair them if necessary. Inspect any electrical connections that are connected to the oxygen sensor. Sometimes the electrical connector may disconnect due to heat and vibration, and the engine error light will come on.

If a code is found, check the operation of the oxygen sensors to make sure they are working properly. Compare the displayed output signals with the values indicated in the manual.

Read the inlet temperature reading of the transducer and then the outlet temperature reading. The difference between the input and output temperatures should be about 100°F. If the temperature difference approaches 200°F or reaches 500°F. Most likely the catalytic converter is damaged.

Test the oxygen sensor, inspect the wires

Check the wiring harness that goes to the oxygen sensor. It’s important to make sure there are no burned out, torn or severely loose spots. Which could hit any moving component while the car is in motion.

Check the operation of the O₂ sensor by thoroughly warming up the engine. Remember that the sensor will work only after it has reached its operating temperature.

Connect the sensor output to a multimeter and start the engine at about 2000-2500 rpm. The output should show a voltage fluctuating between 0.1 and 0.9 V. If the sensor output does not change or the response time is too long. This means that you have a bad oxygen sensor, you should replace it.

Oxygen sensor O₂ replacement will most likely correct the error. But sometimes, you need to replace the catalytic converter to fix the problem. If code P0429 is combined with other codes, try to fix the other codes first.

On which vehicles does this problem occur most frequently

Fault code P0429 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

• Audi
• Ford
• Honda
• Hyundai (Elantra)
• Jeep
• Nissan
• Peugeot
• Saab
• Subaru
• Suzuki (Grand Vitara)
• Toyota
• GAZelle (Next)
• MAZ

Fault code P0429 can sometimes be found with other errors. The most common are the following: P0420, P0421, P0422, P0423, P0424, P0425, P0426, P0427, P0428.

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