Technical Description of OBD-II Trouble Code
Correlation between Catalyst Temperature Sensor 1/2 (Bank 2)
What does that signify?
This is a generic diagnostic trouble code (DTC) for transmission and is applicable to OBD-II vehicles equipped with a catalyst temperature sensor. This may include vehicles from Dodge, Ford, Chevrolet, Dodge, Ram, etc. Although it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
When a vehicle equipped with OBD-II has stored a code P046B, it means that the powertrain control module (PCM) has detected a discrepancy between the temperature signals from the catalytic converter of engine bank two. (Bank 2) refers to the bank of the engine that does not contain the number one cylinder. As far as I know, only diesel applications use catalyst temperature sensors.
Clean burning diesel vehicles require different types of diesel exhaust injections to clear the catalytic converter of harmful emissions. Diesel exhaust fluid (DEF) is injected into the catalytic converter to increase the temperature of the catalyst and burn the nitrogen oxide particles trapped within. These vehicles use catalyst temperature sensors (instead of oxygen sensors) to monitor the efficiency of the catalytic converter. Using temperature to monitor catalyst efficiency is the most accurate and practical method.
Sensor 1 and Sensor 2 may also be referred to as the upstream and downstream catalyst temperature sensors, respectively. These sensors are typically positioned just before and immediately after the catalytic converter in the exhaust system. When the engine is running and sufficiently warmed up, the exhaust entering the catalytic converter should be noticeably cooler than the exhaust exiting the converter. This holds true regardless of the state of the DEF system. The PCM constantly monitors the catalyst temperature sensors and compares the signals from the two sensors. If the degree of variation between the two is not within a programmed range, a code P046B will be stored and a malfunction indicator lamp (MIL) may also illuminate.
What is the severity of this DTC?
Catalyst temperature variation is crucial for reducing exhaust emissions in diesel engines. While this code may not be accompanied by any drivability symptoms, from an environmental perspective, it should be considered severe.
What are some of the symptoms of the code?
Symptoms of a P046B trouble code may include:
What are some of the common causes of the code?
Possible causes for this P046B transmission code may include:
What are some P046B troubleshooting steps?
If I were diagnosing a code P046B, I would recommend having a diagnostic scanner, a digital volt/ohmmeter (DVOM), an infrared thermometer (preferably with a laser pointer), and a reliable vehicle information source (such as AllData DIY).
Ensure that the DEF system is filled with the correct fluid and functioning properly. If there are any DEF-related codes present, I would address and resolve them before attempting to diagnose a P046B. Inspect all wiring and connectors related to the system, with a focus on harnesses located near hot exhaust pipes and manifolds.
Connect the scanner to the vehicle’s diagnostic port and retrieve all stored codes and freeze frame data. Make a note of this information for future reference. Clear the codes and check if the P046D code is reset.
If the code is reset, connect the scanner and observe the data stream while the engine is running at normal operating temperature. It may be helpful to narrow down the data stream to display only relevant data, as this will expedite data delivery and provide a more accurate data signal from the exhaust temperature sensor/s in question.
Refer to your vehicle information source to obtain temperature variance recommendations for the specific vehicle and compare them with the actual data displayed on the scanner data stream.
If the scanner data indicates that the difference between the two sensors is not within specifications, use the infrared thermometer to measure the physical temperature. Compare your findings with the temperature readings on the scanner data display and test the exhaust temperature sensors that do not align.
Use the DVOM to test individual sensors according to the manufacturer’s recommendations. Replace sensors that do not test within specifications.
If all sensors are within specifications, disconnect all related controllers and test individual system circuits. Repair or replace circuits that do not comply with the manufacturer’s specifications.
If all sensors and circuits are within specifications, suspect a defective PCM or a PCM programming error.
