What does it mean?
SPECIAL NOTES: There is a lot of ambiguous, conflicting, and downright incorrect information about catalytic converter temperature sensors available online. One example will suffice: many sources state that oxygen sensors act as temperature sensors. This is not the case- oxygen sensors measure the level of oxygen in exhaust gas, which is a function that is largely independent of the temperature of the exhaust gas after the fuel delivery system enters closed-loop operation.
However, most professional mechanics refer to catalytic converter temperature sensors as “exhaust gas temperature sensors”, which is perhaps a more appropriate name. Nonetheless, exhaust gas temperature sensors can be located in several locations in the exhaust system, with the most common locations being after the turbocharger, upstream of the #1 oxygen sensor, and upstream of the diesel particulate filter on diesel vehicles. END OF SPECIAL NOTES.
OBD II fault code is a generic trouble code that is defined as, P0426 – “Catalytic converter temperature sensor, Bank 1 range/performance”, and is set when the PCM (Powertrain Control Module) detects an incorrect or implausible temperature reading from the sensor that monitors the temperature of the catalytic converter on Bank 1. Note that “Bank 1” refers to the bank of cylinders on V-type engines that contains cylinder #1.
NOTE: On vehicles that do not use catalytic converter temperature sensors, the PCM infers the condition and efficiency of the catalytic converter by comparing the output signals of the upstream and downstream oxygen sensors. As its name suggests, the catalytic converter temperature sensor measures or monitors the temperature of the catalytic materials in the converter.
As such, this measurement plays a critical role in the larger emission control system on vehicles fitted with catalytic converter temperature sensors.
Here is why- Although modern three-way catalytic converters are very efficient at converting harmful exhaust emissions into harmless water and carbon dioxide, the process of converting exhaust gas into innocuous substances only begins to occur when the catalytic materials in the converter are at a temperature of between 500 degrees F and 800 degrees F. Below this temperature range, the exhaust gas passes through the catalytic converter unchanged, which is undesirable.
So, as a practical matter, the catalytic converter has to reach its optimal operating temperature in the shortest possible time to limit the volume of unconverted exhaust gas that the engine emits. In some cases, the PCM uses injection and ignition timing strategies to allow some fuel to ignite in the exhaust manifold, which blows very hot exhaust gas into the catalytic converter.
In other implementations, the catalytic converter uses a dedicated built-in heater element to help heat the catalytic materials to their optimal operating temperature. It is worth noting that on vehicles with fully functional emission control systems, the catalytic converter(s) reach their optimal operating temperature in less than 30 seconds.
At this point, the PCM will recognize that the fuel delivery system has entered closed-loop operation, which means that the PCM uses input data from both the upstream and downstream oxygen sensors to manage the volume of fuel the injectors inject into the cylinders. Put differently, the PCM uses input data from the oxygen sensors to maintain the air/fuel mixture at, or near a stoichiometric ratio, which translates into 14.7 parts of air to one part of fuel in the mixture.
In this ratio, all of the fuel is combusted using all of the available air. However, air/fuel mixtures that contain more (or less) than 14.7 parts of air for each part of fuel will burn hotter or colder than a stoichiometric mixture, but since the PCM cannot monitor the changes in combustion temperatures directly, it uses input data from a dedicated temperature sensor to monitor changes in the temperature of the catalytic converter th