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Home >> Jeep >> 2020 >> Grand Cherokee Trackhawk >> Repair and Diagnosis >> External Pages >> Different car >> Section 284 (8HP75 Automatic Transmission - DTCS P0219-00 To P1D90-00 - 2500HD & 3500HD) >> DTC Troubleshooting >> P0721-00-Output Shaft Speed Sensor Circuit Performance >> Diagnostic Test

Diagnostic Test

WARNING: This page is about a different car, the 2019 RAM 3500 HD and 2019 RAM 2500 HD. However, it is still accessible from the selected car via links, so may be relevant.
  1. CHECK FOR AN ACTIVE CONDITION 
    1. Turn the ignition on.
    2. With the scan tool, erase Transmission Control Module (TCM) Diagnostic Trouble Codes (DTCs).
    3. Raise the vehicle on the hoist.
    4. Start the Engine.
    5. With the scan tool, monitor the Output Speed Sensor RPM.
    6. Firmly apply the brake pedal and place the gear selector in Drive.
      WARNING:

      To avoid personal injury or death, keep hands and feet clear of rotating wheels.

    7. Release the brakes and raise the engine speed to allow the Transmission to perform a 2-3 and 3-4 upshift.

      Did the Output Speed Sensor display a value above 1, 000 RPM?

      Yes 

      • Go To  3

      No 

      • Go To  2.
  2. CHECK IF THE DTC SET DURING A 4L TO 4H SHIFT 
    NOTE:

    The P0721-00 can set during a 4L to 4H transfer case shift if the vehicle transmission is shifted from N to D before the transfer case completes its shift to 4H. If the transmission is shifted to D before the transfer case completes the shift to 4H, the transfer case will default back to 4L, causing the TCM to set this DTC.

    1. Determine if the P0721-00 set following a failed 4L to 4H transfer case shift.

      Did the P0721-00 set during a 4L to 4H transfer case shift?

      Yes 

      No 

      • Go To  3
  3. CHECK TRANSMISSION FOR INTERNAL FAILURE 
    NOTE:

    This DTC is an indication of a internal Transmission failure.

    1. Remove the Transmission Oil Pan and inspect for excessive debris such as clutch friction material or metal contamination.

      Is there any indication of an internal Transmission failure?

      Yes 

      • Repair internal Transmission as necessary in accordance with the Service Information.
      • Perform the TRANSMISSION VERIFICATION TEST. Refer to TRANSMISSION VERIFICATION TEST .

      No 

      • Using the schematics as a guide, check the Transmission Control Module (TCM) connector and all related in-line connector terminals for corrosion, damage, or pushed out terminals. Pay particular attention to the power and ground circuits. If no problems are found, replace and program the TCM in accordance with the Service Information. Refer to MODULE, TRANSMISSION CONTROL (TCM), REMOVAL AND INSTALLATION .
      • Perform the TRANSMISSION VERIFICATION TEST. Refer to TRANSMISSION VERIFICATION TEST .
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