What does it mean?
This diagnostic trouble code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles (Toyota, Jeep, Honda, Nissan, Subaru, GM, Ford, etc.). Although generic, specific repair steps may vary by make/model.
If you’re facing diagnosis of a stored P0429 code, you should know this means the powertrain control module (PCM) has detected a problem with the catalytic converter heater control circuit for engine bank 1. The first bank indicates the malfunction occurred in the catalytic converter for the engine bank containing cylinder #1. Conditions that can cause this code to be stored may be electrical or mechanical.
The main function of the heated catalytic converter is to reduce exhaust emissions from diesel and gasoline engines. It’s a dense filtration element made of ceramic fibers and precious metals enclosed in a steel housing and positioned in the exhaust pipe. Harmful nitrogen oxides (N2O), carbon monoxide, and unburned hydrocarbons are all converted into harmless nitrogen, oxygen, carbon dioxide, and water ions after passing through the heated catalytic converter. This is accomplished using the filtration element and the extreme heat from the engine exhaust.
In the case of the heated catalytic converter, the filtration element is further heated with a PCM-controlled injection of a certain type of flammable diesel exhaust fluid. Catalytic converter temperatures must reach at least 800 degrees Fahrenheit, and heated catalyst units can reach 1,200 degrees Fahrenheit.
The catalytic converter’s efficiency is monitored using upstream and downstream oxygen sensors (O2) and exhaust temperature sensors.
If the heated catalyst isn’t functioning properly, the oxygen concentration variations between input and output exhaust won’t be significant. If the upstream and downstream O2 sensors reflect similar exhaust oxygen concentration, or if an electrical malfunction is detected in the heated catalyst control circuit, a P0429 code will be stored and a malfunction indicator light may illuminate.
Other bank 1 catalyst efficiency trouble codes include:
P0420 Catalyst System Efficiency Below Threshold (Bank 1)
P0421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)
P0422 Main Catalyst Efficiency Below Threshold (Bank 1)
P0423 Heated Catalyst Efficiency Below Threshold (Bank 1)
P0424 Heated Catalyst Temperature Below Threshold (Bank 1)
P0425, P0426, P0427, P0428 Catalyst Temperature Sensor Circuit Codes
Code Severity and Symptoms
Since the catalytic converter heater is crucial for exhaust emission reduction, a P0429 code should be considered severe.
Symptoms of this code may include:
Decreased fuel efficiency
Lack of overall engine performance
Excessive black smoke from exhaust
Other associated diagnostic codes
MIL (Malfunction Indicator Lamp) illumination
Causes
Possible causes for setting this code are as follows:
Faulty exhaust temperature sensor
Incorrect or insufficient diesel exhaust fluid
Faulty diesel exhaust fluid injection system
Burned, rubbed, broken, or disconnected wiring and/or connectors
Faulty O2 sensor(s)
Bad catalytic converter
Engine exhaust leak
Diagnostic and Repair Procedures
A diagnostic scanner, digital volt ohmmeter (DVOM), infrared thermometer (with laser pointer), and a reliable vehicle information source (like All Data DIY) will be needed when diagnosing a P0429 code.
All diesel exhaust fluid injection codes, misfire codes, throttle position sensor codes, manifold air pressure codes, and mass airflow sensor codes should be addressed before attempting to diagnose a stored P0429 code. The engine must be in good working condition before diagnosing this code.
I typically begin my diagnosis with a visual inspection of the system’s wiring harnesses and connectors. I would focus attention on harnesses routed near hot exhaust pipes and manifolds, as well as those routed near sharp edges like those found on exhaust shields.
Next, I would connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes and freeze frame data. I write down this information as it may prove helpful if this turns out to be an intermittent code. Clear the codes and test drive the vehicle to see if P0429 resets.
If applicable, ensure the diesel exhaust fluid tank is filled with the correct fluid and the injection system is functioning properly. If the diesel exhaust fluid injection system fails, the heated catalyst won’t function efficiently and a P0429 code will be stored. If the diesel exhaust fluid injection system isn’t working properly, check the system fuses and relays to ensure the controller is functioning.
If the diesel fluid injection system is working as expected, use the infrared thermometer to test the catalytic converter’s input and output temperatures. Use the vehicle information source and compare actual temperature data with manufacturer specifications. If the output temperature doesn’t meet specifications, suspect a faulty catalytic converter.
If the heated catalyst output temperature meets specifications, use the DVOM to test the exhaust temperature sensor using specifications found in the vehicle information source. Replace the exhaust temperature sensor if it doesn’t meet manufacturer specifications.
Test the O2 sensors following manufacturer recommendations.
Additional diagnostic notes:
P0429 code is frequently stored due to incorrect or insufficient diesel exhaust fluid
Disconnect associated controllers before probing circuits with the DVOM