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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1316 (Transfer Case - NVG 246-NP8 (Two Speed Automatic)) >> Diagnostic Information and Procedures >> DTC C0387 >> Test Description

Test Description

WARNING: This page is about a different car, the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 Chevrolet Tahoe, 2002 Chevrolet Suburban, and 2002 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 3:  Tests whether the transfer case shift control module is sensing any change in all of the encoder channels.
  2. 4:  Helps determine whether the shift is prevented due to a mechanical fault.
  3. 5:  Tests whether the transfer case shift control module is sensing any change in any of the encoder channels.
  4. 6:  Tests if proper reference voltage is being supplied to the encoder from the suspect circuit.
  5. 7:  Helps determine whether a short between 2 or more encoder circuits exist.
  6. 8:  Helps determine whether the shift is prevented due to a mechanical fault.
  7. 9:  Tests for the electrical energizing of the encoder motor.
  8. 10:  Tests the suspect circuit(s) for an open or a short to power.
  9. 11:  Tests for short between the suspect circuits.
DTC C0387

Step Action Value(s) Yes No
Schematic Reference:  Transfer Case Control Schematics  
1 Was the Transfer Case Diagnostic System Check performed? - Go to Step 2  Go to Diagnostic System Check - Transfer Case 
2 Does DTC C0387 set as current? - Go to Step 6  Go to Step 3 
3 
  1. Install a scan tool.
  2. Start the engine.
  3. Place the transmission into NEUTRAL (or clutch pedal depressed on manual transmission applications).
  4. Set the park brake.
  5. Using the scan tool, command through all the shift modes.
  6. Monitor the states of the Encoder P, A, B, and C.
Do all the Encoder Circuits change between ON and OFF?		 - Go to Step 4  Go to Step 5 
4 
  1. Turn the ignition OFF.
  2. Remove the encoder motor. Refer to Transfer Case Motor/Encoder Replacement .
  3. Place a wrench on the end of the transfer case sector shaft and inspect for binding.
Does the sector shaft bind?		 - Go to Step 12  Go to Step 14 
5  Do any of the Encoder Circuits P, A, B, or C change states? - Go to Step 6  Go to Step 9 
6 
  1. Identify which Encoder Circuit(s) did not change.
  2. Turn ON the ignition, with the engine OFF.
  3. Disconnect the six wire connector from the transfer case encoder.
  4. Test the voltage in the suspect circuit(s) to a good ground. Refer to CIRCUIT TESTING and WIRING REPAIRS in Wiring Systems.
Is the voltage reading within the specified values?		 4.8-5.2 V Go to Step 7  Go to Step 10 
7 
  1. Use the scan tool in order to monitor the states of the Encoder Circuit P, A, B, and C.
  2. Individually jumper the each of encoder circuit signal wires at the encoder motor harness connector (one circuit at a time) to ground.
Do each of the Encoder Circuit states display ON when the encoder circuit is shorted to ground?		 - Go to Step 8  Go to Step 11 
8 
  1. Turn OFF the ignition.
  2. Remove the encoder motor. Refer to Transfer Case Motor/Encoder Replacement .
  3. Place a wrench on the end of the transfer case sector shaft and inspect for binding.
Does the sector shaft bind?		 - Go to Step 12  Go to Step 13 
9 
  1. Place the transmission in NEUTRAL.
  2. Start the engine.
  3. Install a scan tool.
  4. Install a DMM on motor control A and motor control B circuits at the transfer case connector, on the module side of the harness
  5. Use the scan tool in order to command the Encoder Motor A and B ON.
Does the DMM display battery voltage?		 - Go to Step 13  Go to Step 14 
10  Test the suspect circuit(s) for an open or a short to power. Refer to CIRCUIT TESTING and WIRING REPAIRS in Wiring Systems.
Was the condition found and corrected?		 - Go to Step 15  Go to Step 14 
11  Test for a short between the suspect circuits. Refer to CIRCUIT TESTING and WIRING REPAIRS in Wiring Systems.
Was the condition found and corrected?		 - Go to Step 15  Go to Step 14 
12 Remove the transfer case and overhaul.
Is the repair complete?		 - Go to Step 15  -
13 Replace the transfer case encoder motor. Refer to Transfer Case Motor/Encoder Replacement .
Is the repair complete?		 - Go to Step 15  -
14 Replace the transfer case shift control module. Refer to Transfer Case Shift Control Module Replacement .
Is the repair complete?		 - Go to Step 15  -
15
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC reset?		 - Go to Step 2  System OK
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