P0439 Catalyst Heater Control Circuit (Bank 2) Trouble Code

P0439 Catalyst Heater Control Circuit (Bank 2)

OBD-II Trouble Code Technical Description

Catalyst Heater Control Circuit (Bank 2)

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles (BMW, Honda, Mitsubishi, Toyota, Ford, Jeep, Hyundai, etc.). Although generic, the specific repair steps may vary depending on make/model.

If you are faced with diagnosing a stored a code P0439, you need to know it means that the powertrain control module (PCM) has detected a problem with the catalyst heater control circuit for engine bank two. Bank 2 specifies that the malfunction has occurred in the catalytic converter for the bank of the engine that does not contain the number one cylinder. Conditions which may cause this code to be stored may be electrical or mechanical.

 

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 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 flowing through the heated catalytic converter. This is accomplished 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 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, variations in oxygen concentration between inlet exhaust and outlet exhaust will not be significant. If 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 be illuminated.

Other bank 2 catalyst efficiency trouble codes include:

P0430 Catalyst System Efficiency Below Threshold (Bank 2) P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2) P0432 Main Catalyst Efficiency Below Threshold (Bank 2) P0433 Heated Catalyst Efficiency Below Threshold (Bank 2) P0434 Heated Catalyst Temperature Below Threshold (Bank 2) P0435, P0436, P0437, P0438 Catalyst Temperature Sensor Circuit Codes

Code Severity & Symptoms

Since the catalyst heater is crucial for exhaust emission reduction, a code P0439 should be considered severe.

Symptoms of this code may include:

Decreased fuel efficiency A lack of general engine performance Excessive black smoke from exhaust Other related diagnostic trouble codes MIL (malfunction indicator lamp) illumination

Causes

Potential causes for this code to set are:

Defective exhaust temperature sensor Improper or insufficient diesel exhaust fluid Malfunctioning diesel exhaust fluid injection system Burnt, chafed, broken, or disconnected wiring and/or connectors Faulty O2 sensor/s Bad catalytic converter Engine exhaust leak

Diagnostic and Repair Procedures

For me, 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) will be required when diagnosing a code P0439.

Any diesel exhaust fluid injection codes, ignition misfire codes, throttle position sensor codes, manifold air pressure codes, and mass air flow sensor codes should be addressed before attempting to diagnose a stored code P0439. T

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