Diagnostic Test

TECH TIPS: 

• Note that the RDM will only have a smart actuator on the two speed systems.
• It is important to remember that the Rear Drive Module (RDM) clutch must engage and bring the propeller shaft up to speed to match the front axle speed for the PTU to engage smoothly and properly when the vehicle is moving. Issues with the hydraulic pump or worn clutches in the RDM can cause poor PTU engagement causing grinding or delayed engagement causing performance faults in the PTU. Any RDM faults or issues should be diagnosed before diagnosing any PTU faults. RDM overtemp faults can be an indicator of a slipping torque transfer clutch assembly.
• If the DTCM is replaced, the Restore Vehicle Configuration procedure must be performed  for the system to operate correctly and not set a configuration mismatch DTC. A configuration mismatch can also set if an incorrect smart actuator is installed.

OVERTEMP DIAGNOSTICS FOR THE RDM SMART ACTUATOR (C140B-4B, C149B-98) AND RDM CLUTCHES (C1472-92, C1477-4B):  If there are any other system faults in the PTU or RDM systems, diagnose the other faults with the PTU or RDM systems. Typically, an issue with one of the assemblies that is causing improper shifting and overworking the system will set other system performance DTCs. If the system only has an overtemp fault, this condition may not require a repair action to correct since the system can set an overtemp fault during extreme use. For the RDM clutch overtemp faults, if the C1477-4B fault is set alone, it is typically caused by overworking the system. If the C1472-92 fault sets along with the C1477-4B fault, it would indicate that there is most likely a system failure with the assembly. Verify the following items before clearing an overtemp fault and returning to the customer.

1. Verify the fluid level and type are correct. For the RDM, also check the differential fluid.
   1. If the fluid is low or appears to be incorrect, top off or change the fluid and retest the system for proper operation. If the fluid is low, perform a visual inspection and repair any leaks found.
   2. If the fluid is full and appears ok, continue testing is step 2.
2. Test drive the vehicle in Auto mode and listen for any grinding or clashing when the PTU is switching modes. This could occur if the propeller shaft is not coming up to speed due to an issue with the RDM clutch, or mechanical issues in the PTU (worn or damaged collar or shaft splines).
   1. If the system appears to be operating and shifting normally, no abnormal noises are heard and the fault does not return, no repair is likely needed, Return the vehicle to the customer and advise that the issue may have been caused by overworking the system.
   2. If the system appears to be operating and shifting normally, but the fault returns, continue to step 3.
   3. If the system is not shifting properly, or is clashing when engaging AWD, verify that the RDM clutches are engaging and bringing the propeller shaft to speed during engagement. Slipping RDM clutches can cause an eventual overheat condition in the RDM. If the RDM is operating normally, replace the PTU in accordance with the service information. If the RDM is not operating properly, replace the RDM in accordance with the service information
3. If one of the smart actuator overtemp faults is present, replace the smart actuator in accordance with the service information. If the C1472-92 fault was present and one or both of the RDM clutch overtemp faults returned, replace the RDM in accordance with the service information.

COMPLETE CIRCUIT AND PERFORMANCE DIAGNOSTICS FOR THE RDM SMART ACTUATOR (C149B-16, C149B-17 C1498-92, C1499-92, C14A8-97): 

1. Using the wiring information as a guide, check the fuse that supplies the Fused B+ circuit for RDM Smart Actuator. Verify the fuse is not open and has a good connection with the terminals in the PDC.
   1. If the fuse is good, continue testing in step 2.
   2. If the fuse is open, check the Fused B+ circuit and for a short to ground before replacing the fuse.
2. Disconnect the smart actuator harness connector. Load test the Fused B+ and ground circuits at the actuator harness connector. With the ignition on, connect one lead of the load test tool to the Fused B+ circuit and the other lead of the load test tool to the ground circuit. The load test bulb should be bright if both circuits are good. To verify that there is no resistance in the circuits being tested, perform a simple voltage drop test across the 3156 bulb of the load test tool. The voltage drop across the bulb should be equal to the voltage reading across the battery terminals if there is no resistance in either circuit.
   NOTE:

   Read the CIRCUIT LOAD TESTING PROCEDURE for information on building the load test tool, additional load testing information and alternative methods of load testing or voltage drop testing a circuit. Refer to CIRCUIT LOAD TESTING PROCEDURES .

   1. If the circuits fail the load test, remove the lead connected to the ground circuit and connect it to a good chassis ground. Check the voltage drop across the 3156 bulb of the load test tool again. If the voltage drop is still less than battery voltage, repair the Fused B+ circuit for an open or high resistance. If the voltage drop is now equal to battery voltage, repair the ground circuit for an open or high resistance.
   2. If the Fused B+ and ground circuits check good, continue to step 3.
3. Verify the fluid level and type are correct.
   1. If the fluid is low or appears to be incorrect, top off or change the fluid and retest the system for proper operation.
   2. If the fluid appears ok, continue testing is step 4.
4. Remove the smart actuator from the RDM. Inspect the shift fork and shaft on the actuator for damage (excessive wear, broken or bent). Also inspect the inside of RDM for signs of damage such as metal particles, damaged splines, collars, gears, etc.
   1. If there does not appear to be any damage inside the assembly, and the shift fork and shaft appear to be ok, replace the smart actuator in accordance with the service information. Retest the system for proper operation. If the fault returns, replace the Rear Drive Module.
   2. If there appears to be damage or metal particles inside the assembly, or the shift fork and shaft appear to damaged or broken, replace the Rear Drive Module in accordance with the service information.