Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnostic Test
2009 Jeep Grand Cherokee SRT-8SECTION Diagnostic Test
- ACTIVE DTC
- REAR DIFFERENTIAL SOLENOID OPERATION
- Turn the ignition off.
- Disconnect the Rear Differential Solenoid harness connector.
- Ignition on, engine not running.
- Using a 12-volt test light, jump across from the (T301) Switch Battery Solenoid Supply circuit and the (T312) Rear Differential Solenoid Control circuit in the Rear Differential Solenoid harness connector.
Does the test light illuminate brightly?
Yes
- Go to step 3
No
- Go to step 4
- (T312) REAR DIFFERENTIAL SOLENOID CONTROL CIRCUIT SHORTED TO GROUND
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- Turn the ignition off.
- Disconnect the FDCM harness connector.
- Measure the resistance of the (T312) Rear Differential Solenoid Control circuit at the FDCM harness connector to ground.
Is the resistance below 5.0 Ohms?
Yes
- Repair the short to ground in the Rear Differential Solenoid Control circuit.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
No
- Go to step 8
- REAR DIFFERENTIAL SOLENOID OPERATION
- Using a 12-volt test light, jump across from the (T301) Switch Battery Solenoid Supply circuit and the (T312) Rear Differential Solenoid Control circuit in the Rear Differential Solenoid harness connector.
- With the scan tool, actuate the Rear Differential Solenoid at 100% duty cycle.
Does the test light illuminate brightly?
Yes
- Replace the Rear Differential Solenoid in accordance with the service information.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
No
- Go to step 5
- (T312) REAR DIFFERENTIAL SOLENOID CONTROL CIRCUIT OPEN
- Measure the resistance of the (T312) Rear Differential Solenoid Control circuit between the Rear Differential Solenoid harness connector and the FDCM harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go to step 6
No
- Repair the open in the (T312) Rear Differential Solenoid Control circuit.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
- Measure the resistance of the (T312) Rear Differential Solenoid Control circuit between the Rear Differential Solenoid harness connector and the FDCM harness connector.
- (T301) SWITCHED BATTERY SOLENOID SUPPLY CIRCUIT SHORTED TO GROUND
- Measure the resistance of the (T301) Switched Battery Solenoid Supply circuit at the Rear Solenoid Differential harness connector to ground.
Is the resistance below 5.0 Ohms?
Yes
- Repair the short to ground in the (T301) Switched Battery Solenoid Supply circuit.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
No
- Go to step 7
- Measure the resistance of the (T301) Switched Battery Solenoid Supply circuit at the Rear Solenoid Differential harness connector to ground.
- (T301) SWITCHED BATTERY SOLENOID SUPPLY CIRCUIT OPEN
- Measure the resistance of the (T301) Switched Battery Solenoid Supply circuit between the Rear Differential Solenoid harness connector and the FDCM harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go to step 8
No
- Repair the open in the (T301) Switched Battery Solenoid Supply circuit.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
- Measure the resistance of the (T301) Switched Battery Solenoid Supply circuit between the Rear Differential Solenoid harness connector and the FDCM harness connector.
- FINAL DRIVE CONTROL MODULE (FDCM) NOTE: Before continuing, check the FDCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
- Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
No
- Replace the Final Drive Control Module (FDCM) in accordance with Service Information.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
- Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
- INTERMITTENT WIRING AND CONNECTORS
- The conditions necessary to set this DTC are not present at this time.
- Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
- Wiggle test the wiring harness and connectors while checking for shorted and open circuits.
- Using the scan tool, monitor the data related to this circuit while performing the wiggle test. Look for the data to change or for the DTC to reset.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the FDCM VERIFICATION TEST. See DTC-Based Diagnostics/MODULE, Final Drive Control (FDCM) - Standard Procedure .
No
- Test complete, the condition or conditions that originally set this DTC are not present at this time.
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.