P0438 indicates the powertrain control module (PCM) has detected a voltage signal from the bank 2 catalyst temperature sensor (sensor 1) that exceeds the expected maximum threshold. This sensor monitors catalytic converter efficiency by measuring exhaust temperature upstream of the converter on the bank 2 cylinder bank.
The sensor element itself has degraded or shorted internally, sending an erroneously high voltage signal to the PCM.
A short to voltage in the sensor signal circuit, damaged insulation, or corroded connector pins can pull the signal voltage high.
An upstream exhaust leak allows outside air to contact the sensor, causing abnormal temperature readings that the PCM interprets as a high circuit voltage.
Misfire, rich fuel condition, or other issues causing excessive exhaust temperatures can drive the sensor reading legitimately high.
Internal PCM driver or processing error for the sensor circuit is possible but rare; verify all wiring and sensor function before considering module replacement.
Almost never. The PCM is the last item to fail; the code is almost always caused by the sensor itself, wiring, or an exhaust leak. Replace the PCM only after every other cause has been ruled out with thorough testing.
No. These sensors are sealed units; contamination or internal failure cannot be fixed by cleaning. If the sensor is faulty, it must be replaced.
Not directly. The code points to a sensor circuit voltage problem. However, an overheating converter (from misfire or rich condition) can cause the sensor to read high, so converter health should be evaluated if no sensor or wiring fault is found.
The MIL may turn off after several drive cycles with no fault detected, but the code will remain in history. Intermittent wiring or connector issues often return unless the root cause is repaired.