This code indicates a fault in the circuit for the second coolant temperature sensor at the outlet of a fuel cell stack (or similar stack cooling system). The control module has detected that the signal from this sensor is out of expected range or is missing. This typically points to a sensor, wiring, or connector problem rather than a control module failure.
The sensor itself has failed internally or its thermistor element has degraded, producing an out-of-range or open signal. This is the most common cause for this code.
Chafed, corroded, or broken wires between the sensor and the control module can interrupt the signal or reference voltage. Heat and vibration near the stack outlet make harness degradation fairly common.
Corroded, bent, or loose terminals at the sensor or control module connector can cause intermittent or permanent signal loss. Moisture intrusion is a frequent contributor.
Degraded or contaminated coolant can coat or foul the sensor element, causing skewed readings. This is less common but worth verifying if coolant condition is poor.
The control module's internal signal circuit has failed. This is rare and should only be considered after all sensor, wiring, and connector checks are completed.
It depends on the system. Many vehicles will enter a limited-power or failsafe mode to protect the stack. Have it diagnosed promptly rather than ignoring it.
No. This sensor monitors coolant at the outlet of a fuel cell or similar stack, not a conventional engine. Diagnosis is similar in principle but the location and system context differ.
Usually no. The control module is the least likely cause. This code is almost always caused by the sensor, wiring, or connector. Replacing the module without thorough testing is a common and costly mistake.
It is possible but uncommon. Severely degraded coolant can foul the sensor element and skew readings, so verifying coolant condition is a reasonable step if no other faults are found.