Diagnostic Overview - AWD System: Notes
A malfunction can cause an immediate fault to set and then eventually set other faults if the malfunction persists. Therefore it may be common to have multiple DTCs with a malfunction. Understanding how the system operates and is monitored can help in determining the likely failure.
The DTCM monitors the bidirectional actuator motor control circuits, internal position sensors and temperature sensors for the PTU and RDM. The DTCM monitors each actuator motors control circuitry for circuit faults (open or shorted) as well as performance faults (free spinning or unable to reach commanded position). The DTCM compares the signal from the position sensors to the commanded position of the actuator motor for determining performance faults.
The sensor supply voltage for both the PTU and RDM hall effect sensors is powered by a common voltage source inside the DTCM. Since both position sensors share a common internal voltage source, a short to ground or battery on either circuit will affect the supply voltage to both sensors. A wiring issue may cause a fault to set against the position sensor for both assemblies, as well as the fault associated with the sensor supply circuit. There is only one fault associated with a failure against either internal position sensor or related circuits for the PTU actuator motor. The same is true for the RDM actuator motor. Each temperature sensor also has only one circuit fault associated to it. This means that if a circuit fault is present for the position or temperature sensor on either assembly, each circuit for that sensor should be checked for opens and shorts.
The position sensors cannot be checked by measuring the voltage on the supply circuit or position sensor circuits. When the connector is unplugged the internal voltage sources are disabled and do not read voltage. The best way to check the circuits is to use a DVOM to check the circuits for opens or shorts.
Overtemp diagnostics: There are different levels of overtemp failures ranging from less severe (overtemp warning) to most severe (permanent actuator shutdown) for each actuator. If only the least severe overtemp fault is set as stored, it may not require a repair action since it is most likely present due to extreme use. If the condition persisted long enough to cause the most severe fault to set, it would indicate that there may be a failure with the actuator or system assembly. Further diagnosis of the system is likely required.