Technical Description of OBD-II Trouble Code
Circuit for Controlling Catalyst Heater (Bank 2)
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles (BMW, Honda, Mitsubishi, Toyota, Ford, Jeep, Hyundai, etc.). Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
If you encounter a stored code P0439, it means that the powertrain control module (PCM) has detected an issue with the circuit for controlling the catalyst heater in engine bank two. Bank 2 indicates that the malfunction has occurred in the catalytic converter for the bank of the engine that does not contain the number one cylinder. The conditions that may cause this code to be stored can be either electrical or mechanical in nature.
The primary function of the heated catalytic converter is to reduce exhaust emissions from diesel and gasoline fueled engines. It is 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 to harmless ions of nitrogen, oxygen, carbon dioxide, and water after passing through the heated catalytic converter. This conversion is achieved using the filtration element and the extreme heat of the engine exhaust.
In the case of the heated catalytic converter, the filtration element is further heated with a PCM controlled injection of some type of flammable diesel exhaust fluid. Catalytic converter temperatures must reach at least 800-degrees Fahrenheit, and heated catalyst units can reach as high as 1,200-degrees Fahrenheit.
Catalytic converter efficiency is monitored using upstream and downstream oxygen (O2) sensors and exhaust temperature sensors.
If the heated catalyst is not functioning properly, there will not be significant variations in oxygen concentration between the inlet exhaust and outlet exhaust. If the upstream and downstream O2 sensors reflect a similar exhaust oxygen concentration, or if an electrical malfunction is detected in the heated catalyst control circuit, a code P0439 will be stored and a malfunction indicator lamp may illuminate.
Other trouble codes related to catalyst efficiency in bank 2 include:
Code Severity & Symptoms
Since the catalyst heater is crucial for reducing exhaust emissions, a code P0439 should be considered severe.
Symptoms of this code may include:
Causes
Potential causes for this code to be set are:
Diagnostic and Repair Procedures
To diagnose a code P0439, you will need a diagnostic scanner, a digital volt ohmmeter (DVOM), an infrared thermometer (with a laser pointer), and a reliable vehicle information source (such as All Data DIY).
Before attempting to diagnose a stored code P0439, address any diesel exhaust fluid injection codes, ignition misfire codes, throttle position sensor codes, manifold air pressure codes, and mass air flow sensor codes. The engine must be in good running order before diagnosing this code.
Begin the diagnosis with a visual inspection of the system’s wiring harnesses and connectors. Pay close attention to harnesses that are routed near hot exhaust pipes and manifolds, as well as those that are routed near sharp edges like the ones found on exhaust shields.
Next, connect the scanner to the vehicle’s diagnostic port and retrieve all trouble codes and freeze frame data. Write down this information as it may be useful if the code proves to be intermittent. Clear the codes and test drive the vehicle to see if the P0439 code is reset.
If applicable, ensure that the diesel exhaust fluid reservoir is filled with the correct fluid and that the injection system is functioning properly. If the diesel exhaust fluid injection system fails, the heated catalyst will not function efficiently and a code P0439 will be stored. If the diesel exhaust fluid injection system is not working properly, check the system’s fuses and relays to ensure that the controller is operable.
If the diesel fluid injection system is functioning as designed, use the infrared thermometer to test the input and output temperatures of the catalytic converter. Consult the vehicle information source and compare the actual temperature data with the manufacturer’s specifications. If the output temperature is not within specifications, suspect a defective catalytic converter.
If the output temperature of the heated catalyst meets specifications, use the DVOM to test the exhaust temperature sensor using the specifications found in the vehicle information source. Replace the exhaust temperature sensor if it fails to comply with the manufacturer’s specifications.
Test the O2 sensors following the manufacturer’s recommendations.
Additional diagnostic notes:
