|Trouble Code||Fault Location||Probable Cause|
|P2031||Exhaust gas temperature (EGT) sensor 2, bank 1 - circuit malfunction||Wiring, EGT sensor|
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What Does Code P2031 Mean?
OBD II fault code P2031 is a generic code that is defined as ““Exhaust gas temperature (EGT) sensor 2, bank 1 – circuit malfunction”, and is set when the PCM (Powertrain Control Module) detects a general malfunction in the control circuit of the #2 EGT (Exhaust Gas Temperature) sensor (or in the sensor itself) fitted to the exhaust system of bank 1. “Bank 1” refers to the bank of cylinders that does contains cylinder #1, while sensor #2 most commonly refers to the exhaust gas temperature sensor that is fitted downstream of the catalytic converter.
On all applications that are fitted with exhaust gas temperature sensors, the PCM uses input data from EGT sensors located on either side of the catalytic converter both to monitor the efficiency of the converter, and to calculate appropriate strategies to bring about a either reduction or an increase in the exhaust gas temperature.
If the exhaust has is too hot, the PCM can initiate a strategy such as disabling some fuel injectors and spark plugs (or injecting additional ambient air into the exhaust system via the secondary air injection system) to allow relatively cool air to pass through the converter as a means to protect the catalytic converter against the effects of overheating. If on the other hand, the exhaust gas is too cool, the PCM can alter the ignition timing and/or fuel delivery to increase the exhaust gas temperature as a means to increase the efficiency of the catalytic converter.
Note however that while there are many possible reasons why the temperature of the exhaust gas could exceed or fall below predefined maximum/minimum allowable thresholds, the function of the exhaust gas temperature sensor(s) is limited to indicating that the exhaust gas is either above, or below acceptable/desired thresholds.
NOTE: The root causes of the excessively hot (or cold) exhaust gas will almost certainly be indicated by other, dedicated codes that could include fuel/air metering related codes, and/or by codes relating to malfunctions of other exhaust sensors, which malfunctions can sometimes contribute to the setting of code P2031.
In terms of operation, exhaust gas temperature sensors are most commonly simple temperature sensors, or thermocouples, of the temperature reactive resistor variety that use a 5-volt reference voltage to generate a signal voltage. On most applications, the sensor’s resistance decreases as it heats up, thus allowing more current to be passed back to the PCM via a dedicated signal circuit. Conversely, the sensor’s resistance increases as it cools down, thereby allowing less current to be passed back to the PCM.
In practice, the PCM interprets the changing signal current as changing degrees of temperature, and by comparing the input data it receives from both the upstream and downstream exhaust gas temperature sensors in near-real time, it can calculate an efficiency factor for the catalytic converter. However, should a failure occur in the #2 (downstream) EGT sensor and/or its control/signal circuit(s),the PCM can no longer effectively monitor the operation of the catalytic converter, (or initiate corrective measures if required), and it well set code P2031 as a result.
Note that on some applications, the PCM will also illuminate a warning light immediately when the failure is detected, while on others, the fault needs to be registered several times before a warning light will be illuminated. In these cases, code P2031 will be stored as a “pending” code.
Where is the P2031 sensor located?
The image above shows the typical location of exhaust gas temperature sensors on either side of a catalytic converter. Note the presence of other, unrelated sensors that must not be confused with the exhaust temperature sensors.
NOTE: Diesel exhaust systems are fitted with DPF’s (Diesel Particulate Filters, but not shown here) whose operation and regeneration largely depend on exhaust gas temperature sensors, one of which is fitted upstream and downstream of the DPF. Moreover, advanced exhaust systems are also fitted with several other sensors, such as NOx -, oxygen -, pressure sensors, and sometimes pressure differential sensors, whose labelling or numbering in the system may vary between manufacturers.
Therefore, it is important always to refer to the manual for the affected application to locate and identify exhaust gas temperature sensors correctly. Failure to do this will almost certainly result in wasted time, misdiagnoses, and the distinct possibility that expensive exhaust components may be replaced in error.
What are the common causes of code P2031?
Some common causes of code P2031 could include the following-
- Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
- Poor electrical connections
- Defective exhaust gas temperature sensor
- Making unauthorized modifications to the exhaust system. These could include fitting a “cat back” system in which the catalytic converter(s) and associated sensors are removed from the exhaust system, or by bypassing these components in various ways to improve engine performance. Note that this practice is a federal offence.
- Failed or failing PCM. Note that his is a rare event, and the fault must therefore be sought elsewhere before any control module is replaced