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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1072 (Automatic Transmission - ALLISON, Diagnosis (DTC P0736 To DTC P0872)) >> Diagnosis >> DTC P0848 >> Test Description

Test Description

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The numbers below refer to the step numbers on the diagnostic table.

  1. 5:  This step tests the TCM response function.
  2. 6:  This step tests the transmission wiring harness integrity.
  3. 7:  This step tests and evaluates the internal wiring harness.
  4. 8:  This step tests the PSM for a failed condition.
DTC P0848

Step Action Value Yes No
Schematic Reference: Automatic Transmission Controls Schematics
1 Did you perform the Diagnostic System Check - Automatic Transmission? - Go to Step 2  Go to Diagnostic System Check - Automatic Transmission
2 Measure the transmission fluid level. Refer to Transmission Fluid Checking Procedure .
Is the transmission fluid level correct?		 - Go to Step 3  Go to Transmission Fluid Checking Procedure
3 Measure line pressure. Refer to Line Pressure Check Procedure .
Is the pressure within the specified value?		 - Go to Step 4  Go to Symptoms - Automatic Transmission
4
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
    3. IMPORTANT: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.
  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Start the engine.
  6. Using the scan tool, monitor TFP SW. D status.
Does the scan tool indicate TFP SW. D status in ON?		 - Go to Diagnostic Aids Go to Step 5 
5 
  1. Turn the ignition OFF.
  2. Disconnect C2 connector (RED) at the TCM.
  3. Install the J 39700  breakout box and the J 43799  breakout box adapter at C2 connector.
  4. Connect terminal 2 to a known good ground.
  5. Turn ON the ignition, with the engine OFF.
Does the scan tool indicate TFP SW. D status is ON when grounded and OFF when open?		 - Go to Step 6  Go to Step 15 
6 
  1. Turn the ignition OFF.
  2. Connect the C2 connector (RED) to the TCM.
  3. Disconnect the transmission 20-way connector.
  4. Turn the ignition ON. Additional DTCs might be set.
  5. Connect terminal F to a known good ground.
Does the scan tool indicate TFP SW. D status is ON when grounded and OFF when open?		 - Go to Step 7  Go to Step 14 
7 
  1. Remove the oil pan. Refer to Oil Pan Replacement .
  2. Disconnect the AT internal wiring harness from the PSM and ground terminal B.
Does the scan tool indicate TFP SW. D status is ON when grounded and OFF when open?		 - Go to Step 8  Go to Step 13 
8 
  1. Remove the PSM from the control valve body and leave the internal harness connected. Refer to Pressure Switch Manifold Replacement .
  2. Provide a ground connection for the PSM to either the control valve body or the transmission main case.
  3. Using the eraser end of a pencil, push gently on the pressure switch D membrane.
Does the scan tool indicate TFP SW. D status is ON when grounded and OFF when open?		 - Go to Step 9  Go to Step 12 
9 Remove the control valve body and inspect for a stuck or sticking D shift valve. Refer to Control Valve Body Disassemble .
Was the D shift valve stuck or sticking?		 - Go to Step 11  Go to Step 10 
10 Replace the D shift solenoid and install the control valve body. Refer to Control Valve Body Replacement .
Did you complete the replacement of the solenoid and installation of the valve body?		 - Go to Step 16  -
11 Replace the control valve body assembly. Refer to Control Valve Body Replacement .
Did you complete the replacement?		 - Go to Step 16  -
12 Replace the PSM. Pressure Switch Manifold Replacement .
Did you complete the replacement?		 - Go to Step 16  -
13 Replace the AT internal wiring harness. Refer to Wiring Harness Replacement .
Did you complete the replacement?		 - Go to Step 16  -
14 Repair the engine wiring harness circuit for an open or short. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 16  -
15
IMPORTANT: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
Replace the TCM. Refer to Transmission Control Module (TCM) Replacement .Did you complete the replacement?		 - Go to Step 16  -
16 Perform the following procedure in order to verify the repair:
  1. Clear the DTC.
  2. Start the engine.
  3. Using the scan tool, monitor TFP SW. D status.
  4. Select Specific DTC.
  5. Enter DTC P0848.

Has the test run and passed?		 - System OK Go to Step 1 
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