Transfer Case - Diagnosis - New Venture 246 Cadillac Escalade GMT400

APPLICATION

TRANSFER CASE APPLICATIONS

DESCRIPTION

New Venture 246 transfer case is a 2-speed unit that utilizes a part time front axle. Transfer case unit has a 2-piece magnesium case. System allows driver to select transfer case position with the touch of a button. Transfer case has 5 shift positions; 4-Wheel Drive High (4H), All Wheel Drive (AUTO), 2-Wheel Drive High (2H), Neutral (N) and 4-Wheel Drive Low (4L). Automatic Transfer Case (ATC) control module controls all shifting action of transfer case based on input from driver and information from Powertrain Control Module (PCM) and Vehicle Control Module (VCM).

OPERATION

ATC control module can engage front drive axle while vehicle is in motion. It applies a pulse width modulated signal to electric motor, which transfers torque to front axle. This action matches speed of front and rear drive shafts. After drive shaft speeds are matched, control module completes ground circuit to front axle actuator to engage front drive axle.

ATC control module will allow a mode shift only when engine is running and valid motor/encoder signal is present. A mode shift is any shift between 2H, 4H and AUTO.

ATC control module will allow a range shift only if the following conditions are met within 30 seconds of request: engine is running, transmission is in Neutral, vehicle speed is less than 3 MPH and proper motor/encoder signal is present. A range shift is a shift between 2H, 4H, AUTO (high range) and 4L (low range). ATC control module will permit a range shift into or out of Neutral only if the following conditions are met: ignition is on, transmission is in Neutral and vehicle speed is zero.

4WD mode (4H or 4L) is accomplished by engaging front axle, applying pulse width modulated signal to electric motor to apply maximum torque (fully compressing transfer case clutch plates) to front drive axle. ATC control module, then opens ground circuit, which locks motor in position and stops pulse width modulated signal to electric motor. In AUTO mode, system should engage front drive axle, then monitor front and rear drive shaft speeds for speed differential. (Scheme 1) When system senses rear wheel slip, or a difference in drive shaft speed between front and rear drive shafts, ATC control module will use pulse width modulated signal to operate electric motor. Motor transfers only required torque to front wheels to gain additional traction on slippery surfaces up to 75 MPH. There is no torque applied to front wheels until ATC control module senses rear wheel slip.

Throttle anticipation, which is only operational in AUTO mode, occurs if vehicle speed is less than 5 MPH and accelerator is pressed quickly beyond a set point. System will automatically transfer a percentage of torque to front wheels to help prevent rear wheels from slipping, such as in hard acceleration from a stopped position.

Scheme 1

PRELIMINARY DIAGNOSIS

1. Ensure all mechanical components are operating properly before diagnosing electrical system. To determine if vehicle is in 2WD or 4WD, lift vehicle so wheels can spin freely while changing between 2WD and 4WD settings.
2. Ensure system fuses in instrument panel fuse block and in underhood bussed electrical center are not open. If any fuse is open, locate and repair source of fuse or circuit overload. Replace fuses before proceeding.
3. Check for broken or partially broken wire inside of insulation which could cause system failure, but will appear okay during continuity or voltage checks with system disconnected. Check circuits by monitoring fuse voltage drop with system operational (under load). Ensure aftermarket equipment (if equipped) which may affect integrity of electronic systems has been installed properly.

TRANSFER CASE SYSTEM CHECK

Before proceeding with transfer case electronic controls diagnosis, perform the following test procedure. This procedure checks Class II communication between Automatic Transfer Case (ATC) control module and scan tool, checks static system operation, and also checks Park/Neutral switch input operation.

1. Turn ignition off. Connect scan tool to DLC. Turn ignition switch to run position (engine off). Use scan tool to communicate with ATC control module. If communication link is okay, go to next step. If communication is not okay, diagnose Data Link Connector (DLC) for malfunction. See DLC DIAGNOSIS OR NO SCAN TOOL DATA in SELF-DIAGNOSTICS - GASOLINE - EXCEPT METRO, PRIZM & TRACKER article in ENGINE PERFORMANCE.
2. Using scan tool, check for any DTC in ATC control module. If any DTC is present, go to step 6 . If no DTCs are present, go to next step.
3. If any History DTC is present, go to step 10 . If no History DTC is present, go to next step.
4. With scan tool installed, set parking brake, depress and hold foot brake, start engine and shift transmission to Neutral position. Read Encoder Gear Position on scan tool while shifting transfer case through all modes. Allow time for system to complete each shift request. If scan tool shows correct gear positions, go to next step. If scan tool does not show correct gear position, see «SELECT SWITCH INOPERATIVE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__select-switch-inoperative) under SYMPTOM DIAGNOSIS.
5. If all of the mode switch indicator lights light when the corresponding switch is depressed, go to next step. If indicator lights do not light when switch is depressed, see «ONE OR MORE SELECT SWITCH INDICATOR LIGHTS DO NOT LIGHT»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__1-or-more-select-switch-indicator) under SYMPTOM TESTS.
6. If SERVICE indicator light on instrument cluster has turned on, go to «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) table. If light does not come on, see «SERVICE 4WD INDICATOR DOES NOT LIGHT»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__service-4wd-indicator-does-not-light) under SYMPTOM TESTS.
7. If vehicle was brought in with a driveability complaint, see appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. If vehicle was not brought in with a driveability complaint, go to next step.
8. Road test vehicle if needed to verify customer complaint. After road test, use scan tool to check for DTC. If any DTC is present, see appropriate DTC test. If no DTC is present, go to next step.
9. If any mechanical problems were noted during road test, make appropriate repairs before continuing. If no mechanical problems were noted, system is operating properly.
10. If a History DTC is present, it indicates the DTC was repaired, but code was not cleared or problem is intermittent. Record any History DTCs. Clear all DTCs, then road test vehicle. Attempt to engage AWD. Following road test, check for DTCs. If any DTC is present, see «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) table. If no DTC is present, go to next step.
11. Confirm that repairs were completed. If not, make appropriate repairs as needed, or go to step 1 .

CONDITIONS FOR CLEARING DTC

ATC control module will clear DTC if condition for setting this DTC no longer exists. Stored DTC will clear after 100 ignition cycles without a fault present. Use scan tool to clear stored DTC.

Note. For control module, select switch, motor/encoder and axle actuator connector terminal location and identification on transfer case (Scheme 2)- (Scheme 8). For circuit identification and wire colors, see WIRING DIAGRAMS.

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Scheme 6

Scheme 7

Scheme 8

DIAGNOSTIC TROUBLE CODE DEFINITIONS

DIAGNOSTIC TROUBLE CODE DEFINITIONS

Circuit Description

Automatic Transfer Case (ATC) control module controls SERVICE indicator light in instrument cluster. Ground is provided by Light Blue/Black wire and power is supplied by Pink wire from GAUGES fuse (10-amp), in instrument panel fuse block.

Conditions For Setting DTC

Code B0768 is set when control module turns indicator light on, and senses voltage of more than 7 volts on Light Blue/Black wire.

Testing

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).
2. Turn ignition off. Disconnect instrument cluster connector. Inspect connector terminals for damage or corrosion. If terminals are damaged, go to step 5. If terminals are okay, go to next step.
3. Disconnect instrument cluster harness connector. Disconnect both ATC control module connectors C1 and C2. Turn ignition on. Measure voltage of Light blue/Black wire between control module C1 connector terminal E2 and ground. (Scheme 2) If voltage is more than zero volts, go to next step. If voltage is zero volts, go to step 6.
4. Repair short to voltage in Light Blue/Black wire. When repair is complete, go to step 11.
5. Repair instrument cluster harness connector. When repair is complete, go to step 11.
6. Turn ignition off. Reconnect instrument cluster connector. Connect fused jumper (3-amp) wire between control module connector C1 terminal E2 (Light Blue/Black wire) and ground. Turn ignition on. If SERVICE indicator lights, go to next step. If SERVICE indicator does not light, go to step 8.
7. Replace ATC control module. When repair is complete, go to step 11.
8. Check SERVICE indicator for good bulb. If bulb is good, go to step 10. If bulb is faulty, go to next step.
9. Replace bulb. When repair is complete, go to step 11.
10. Service problem in instrument cluster. See appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. When repair is complete, go to next step.
11. Turn ignition off. Reconnect all disconnected components. When repair is complete, go to next step.
12. Use scan tool to clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).

Automatic Transfer Case (ATC) control module interfaces with 4 normally open push button switches. Switch assembly, located on instrument panel, uses a resistor network to provide analog voltage signal to ATC control module to determine 4H, AUTO (Adapt), 2H, N and 4L shift request. Control module supplies 8 volts to switch assembly through Light Green/Black wire circuit and reads voltage level back on Light Blue wire circuit. When DTC B2725 is set, an open, short to ground or short to voltage condition exists, or switch assembly fault has occurred.

System constantly monitors voltage on Light Blue wire circuit. If improper voltage level is detected outside .5-1.0 volts when no buttons are depressed, DTC B2725 is set. Shift will be disabled and SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).
2. Turn ignition off. Disconnect transfer case select switch connectors C1 and C2. Turn ignition on. Measure voltage between ground and Light Green/Black wire select switch connector C1 terminal "A". See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246). If voltage is 7-9 volts, go to next step. If voltage is not 7-9 volts, go to step 9.
3. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Turn ignition to run position (engine off). Measure voltage between front ATC control module connector C1 terminal F16 (Light Blue wire) and ground. If voltage is more than zero, go to step 11. If voltage is zero, go to next step.
4. Turn ignition off. Measure resistance of Light Blue wire between ground and transfer case select switch connector C1 terminal "B". If resistance is less than infinite, go to next step. If resistance is infinite, go to step 6.
5. Locate and repair short to ground in Light Blue wire. When repair is complete, go to step 18.
6. Measure resistance of Light Blue wire between terminal "B" of select switch connector C1 and ATC control module connector C1 terminal F16. (Scheme 2)and (Scheme 4). If resistance is 0-2 ohms, go to next step. If resistance is more than 2 ohms, go to step 8.
7. Replace transfer case select switch. See «TRANSFER CASE SELECT SWITCH»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When replacement is complete, go to step 18.
8. Locate and repair open in Light Blue wire between ATC control module and transfer case select switch connector. When repair is complete, go to step 18.
9. If voltage in step 2 was more than 9 volts, go to next step. If voltage in step 2 was less than 9 volts, go to step 14.
10. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Turn ignition on. Measure voltage between of Light Green/Black wire between transfer case select switch connector C1 terminal "A" and ground If voltage is zero, go to step 12. If voltage is more than zero, go to step 13.
11. Locate and repair short to voltage in Light Blue wire. When repair is complete, go to step 18.
12. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 18.
13. Locate and repair short to voltage in Light Green/Black wire. When repair is complete, go to step 18.
14. Disconnect ATC control module connectors. Measure resistance of Light Green/Black wire between terminal "A" in select switch connector C1 and ground. If resistance is less than infinite, go to next step. If resistance is infinite, go to step 16.
15. Locate and repair short to ground in Light Green/Black wire. When repair is complete, go to step 18.
16. Measure resistance of Light Green/Black wire between select switch C1 connector terminal "A" and ATC control module C1 connector terminal F14. See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246). If resistance is 0-2 ohms, go to step 12. If resistance is more than 2 ohms, go to next step.
17. Locate and repair open in Light Green/Black wire between select switch connector and ATC control module connector. When repair is complete, go to next step.
18. Turn ignition off. Reconnect all disconnected components. When complete, use scan tool to clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).

Rear drive shaft speed sensors are a Permanent Magnet (PM) generator. Sensors produce a pulsing AC voltage. AC voltage level and number of pulses increases as speed increases. ATC control module converts pulsating AC voltage to drive shaft RPM which is used for calculations and to monitor difference between front and rear drive shaft speed. Drive shaft RPM can be displayed using scan tool. ATC control module only monitors this signal when vehicle is in 2H position. DTC C0300 detects open, short to ground or faulty sensor.

System will set DTC if rear drive shaft input indicates speed of less than 16 RPM for 30 seconds when following conditions are present

1. Transmission is not in Park or Neutral.
2. Engine is running.
3. Front axle is engaged.
4. Rear drive shaft speed exceeds 512 RPM.
5. Vehicle speed on Class 2 Data Bus exceeds 10 MPH.

When this DTC is set, all shifts to AUTO mode will be disabled. System will not allow any further adaptive events (slip corrections). SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Connect scan tool. Turn ignition to run position (engine off). Check for powertrain DTCs. If any Vehicle Speed DTC is found, see appropriate powertrain DTC test article in ENGINE PERFORMANCE manual. If no powertrain DTC is noted, go to next step.
3. With scan tool connected, drive vehicle with assistant. Observe ATC Data List. Note value of Rear Drive Shaft Speed at a set speed. Change scan tool screen to reflect Transmission Data List. Compare Rear Drive Shaft Speed as recorded to Transmission Output Shaft Speed (OSS) at same speed. If RPM values are equal at same speeds, go to step 22 . If RPM values are different at same speeds, go to next step.
4. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Connect DVOM between ATC control module connector C1 terminals F5 (Light Blue wire) and F6 (Dark Green wire). Block front wheels. Place transmission in Neutral position. Raise and support rear of vehicle so wheels turn freely. Turn rear drive shaft by hand and note AC voltage. If voltage is 0-0.5 volt, go to step 20 . If voltage is more than .5 volt, go to next step.
5. Disconnect transfer case rear drive shaft speed sensor. Measure resistance between speed sensor terminals. If resistance is 1300-2700 ohms, go to next step. If resistance is not 1300-2700 ohms, go to step 21 .
6. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Measure resistance between Dark Green and Light Blue wire terminals of control module connector C1. If resistance is infinite, go to next step. If resistance is less than infinite, go to step 15 .
7. Turn ignition on. Measure voltage of Dark Green wire between control module connector C1 and ground. If voltage is more than zero volts, go to step 16 . If voltage is zero, go to next step.
8. Turn ignition off. Measure resistance of Dark Green wire between control module connector C1 and ground. If resistance is less than infinite, go to step 17 . If resistance is infinite, go to next step.
9. Turn ignition on. Measure voltage of Light Blue wire between control module connector C1 and ground. If voltage is more than zero volts, go to step 18 . If voltage is zero, go to next step.
10. Turn ignition off. Measure resistance of Light Blue wire between control module connector C1 and ground. If resistance is less than infinite, go to step 19 . If resistance is infinite, go to next step.
11. Measure resistance of Dark Green wire between control module connector C1 and rear speed sensor connector. If resistance is 0-2 ohms, go to next step. If resistance is more than 2 ohms, go to step 14 .
12. Measure resistance of Light Blue wire between control module connector C1 and rear speed sensor connector. If resistance is 0-2 ohms, go to step 22 . If resistance is more than 2 ohms, go to next step.
13. Repair open in Light Blue wire. When repair is complete, go to step 22 .
14. Repair open in Dark Green wire. When repair is complete, go to step 22 .
15. Repair short between Dark Green and Light Blue wires. When repair is complete, go to step 22 .
16. Repair short to voltage in dark Green wire. When repair is complete, go to step 22 .
17. Repair short to ground in Dark Green wire. When repair is complete, go to step 22 .
18. Repair short to voltage in Light Blue wire. When repair is complete, go to step 22 .
19. Repair short to ground in Light Blue wire. When repair is complete, go to step 22 .
20. Replace ATC control module. When repair is complete, go to step 22 .
21. Replace rear speed sensor. When repair is complete, go to next step.
22. Turn ignition off. Reconnect all disconnected components. Go to next step.
23. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

Front drive shaft speed sensor is a permanent magnet (PM) generator. Sensor produces a pulsing AC voltage. AC voltage level and number of pulses increases as speed increases. ATC control module converts pulsating AC voltage to drive shaft RPM, which is used for calculations and to monitor differences between front and rear drive shaft speed. It is also used in AUTO mode to determine amount of slip and percent of torque to apply to front axle. Drive shaft RPM can be displayed using scan tool. ATC control module only monitors this signal when vehicle is in AUTO, 4H and 4L positions. DTC C0305 detects an open, short to ground or faulty sensor.

System will set DTC if front drive shaft input indicates speed of less than 16 RPM for 30 seconds when following conditions are present

1. Transmission is not in Park or Neutral.
2. Engine is running.
3. Front axle is engaged.
4. Rear drive shaft speed exceeds 512 RPM.
5. Vehicle speed on Class 2 Data Bus exceeds 10 MPH.

When this DTC is set, all shifts to AUTO mode will be disabled. On both transfer cases, system will not allow any further adaptive events (slip corrections). SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Connect scan tool. Turn ignition on. Check for powertrain DTCs. If any Vehicle Speed DTC is found, see appropriate powertrain DTC test article in ENGINE PERFORMANCE manual. If no powertrain DTC is noted, go to next step.
3. With scan tool connected, drive vehicle with assistant. Observe ATC Data List. Note value of Front Drive Shaft Speed at a set speed. Compare Rear Drive Shaft Speed as recorded to Front Drive Shaft Speed at same speed. If RPM values are within 10 percent at same speeds, go to step 22 . If RPM values are not within 10 percent, go to next step.
4. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Connect DVOM between ATC control module connector C1 terminals E12 (Yellow wire) and E13 (Purple wire). Block rear wheels. Place transmission in Neutral position. Raise and support front of vehicle so wheels turn freely. Turn front drive shaft by hand and check AC voltage. If voltage is 0-0.5 volt, go to step 20 . If voltage is more than .5 volt, go to next step.
5. Disconnect transfer case front drive shaft speed sensor. Measure resistance between speed sensor terminals. If resistance is 1300-2700 ohms, go to next step. If resistance is not 1300-2700 ohms, go to step 21 .
6. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Measure resistance between Yellow and Purple wire terminals of control module connector C1. If resistance is infinite, go to next step. If resistance is less than infinite, go to step 15 .
7. Turn ignition on. Measure voltage of Yellow wire between control module connector C1 and ground. If voltage is more than zero volts, go to step 16 . If voltage is zero, go to next step.
8. Turn ignition off. Measure resistance of Yellow wire between control module connector C1 and ground. If resistance is less than infinite, go to step 17 . If resistance is infinite, go to next step.
9. Turn ignition on. Measure voltage of Purple wire between control module connector C1 and ground. If voltage is more than zero volts, go to step 18 . If voltage is zero, go to next step.
10. Turn ignition off. Measure resistance of Purple wire between control module connector C1 and ground. If resistance is less than infinite, go to step 19 . If resistance is infinite, go to next step.
11. Measure resistance of Yellow wire between control module connector C1 and front speed sensor connector. If resistance is 0-2 ohms, go to next step. If resistance is more than 2 ohms, go to step 13 .
12. Measure resistance of Purple wire between control module connector C1 and front speed sensor connector. If resistance is 0-2 ohms, go to step 22 . If resistance is more than 2 ohms, go to next step.
13. Repair open in Yellow wire. When repair is complete, go to step 22 .
14. Repair open in Purple wire. When repair is complete, go to step 22 .
15. Repair short between Yellow and Purple wires. When repair is complete, go to step 22 .
16. Repair short to voltage in Yellow wire. When repair is complete, go to step 22 .
17. Repair short to ground in Yellow wire. When repair is complete, go to step 22 .
18. Repair short to voltage in Purple wire. When repair is complete, go to step 22 .
19. Repair short to ground in Purple wire. When repair is complete, go to step 22 .
20. Replace ATC control module. When repair is complete, go to step 22 .
21. Replace front speed sensor. When repair is complete, go to next step.
22. Turn ignition off. Reconnect all disconnected components. Go to next step.
23. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

The transfer case motor is a bi-directional, permanent magnet, DC motor. When energized, (through Motor Control A or Motor Control B, the ground is provided by the opposing Motor Control circuit and then grounded through the shift control module ground circuit), the motor, through a series of gears, rotates a shaft which moves the mode and range forks to shift the between 4HI, AUTO 4WD, 2HI, N, and 4LO ranges. While the transfer case motor is energized the shift control module also energizes the solenoid for the transfer case lock. The motor lock is disabled (locking action released) and free turning of the transfer case motor and sector shaft is then allowed.

This DTC detects a short to ground in Motor Control A or Motor Control B CKT.

1. The system will test the motor circuits: First, the system checks for unwanted voltage. Then, the system supplies voltage on one circuit and reads the voltage back on the other.
2. If the system detects a problem with the circuits, the DTC is logged.
3. The shift control module senses a low voltage return in Motor Control A or Motor Control B when a high voltage is expected.

Action Taken When The DTC Sets

1. All shifting will be disabled.
2. The SERVICE 4WD indicator will be latched on for the remainder of the current ignition cycle.

Conditions For Clearing The DTC

1. The shift control module will clear the DTC if the condition for setting the DTC no longer exists.
2. A history DTC will clear after 100 consecutive ignition cycles without a fault present.
3. History DTCs can be cleared using a scan tool.

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

1. 2 - Listen for an audible motor noise when the encoder motor operates. Command both the ON and OFF states. Repeat the commands as necessary.
2. 3 - Tests for a short to ground in the Motor Control A circuit.
3. 4 - Tests for a short to ground in the Motor Control B circuit.
4. 5 - Tests for a higher than normal resistance in the Motor Control A and B circuits through the module.
5. 6 - Tests for a short to ground in the encoder motor windings.
6. 7 - Tests for continuity across the motor circuit. Resistance readings vary depending on the location of the brush contact inside the motor assembly.
7. 8 - Tests Motor Feed A circuit for a short to ground.
8. 9 - Tests Motor Feed B circuit for a short to ground.
9. 10 - Tests Motor Feed A and B circuits for an open or high resistance.

Scheme 9

Scheme 10

Transfer case shift motor is a bi-directional, Permanent Magnet, DC motor. The motor rotates a shaft, through a series of gears, which moves mode and range forks to shift transfer case into specific range. DTC C0309 detects short to voltage or faulty motor.

System will test motor circuits as follows

1. System checks voltage on each circuit.
2. System supplies voltage on one circuit and reads voltage back on other circuit.
3. If system detects a problem, DTC is set.
4. ATC control module senses high voltage on either circuit when a low voltage signal is expected.

When this DTC is set, all shifting will be disabled. SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).
2. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Disconnect transfer case shift motor connector. Turn ignition on. Measure voltage of Black wire between ATC control module C2 connector terminal "A" and ground. (Scheme 3) If voltage is more than zero volts, go to next step. If voltage is zero volts, go to step 5.
3. Turn ignition off. Disconnect transfer case motor/encoder connector. Turn ignition on. Measure voltage of Black wire between ATC control module C2 connector terminal "A" and ground. (Scheme 3) If voltage is more than zero volts, go to next step. If voltage is zero volts, go to step 6.
4. Repair short to voltage in Black wire. When repair is complete, go to step 7.
5. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 7.
6. Repair short to voltage in Black wire. When repair is complete, go to next step.
7. Turn ignition off. Reconnect all disconnected components. Go to next step.
8. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).

Transfer case shift motor is a bidirectional, permanent magnet, DC motor. The motor rotates a shaft, through a series of gears, which moves mode and range forks to shift transfer case into specific range. DTC C0310 detects open circuits or open motor.

System will test motor circuits as follows

1. System checks for unwanted voltage.
2. System supplies voltage on one circuit and reads voltage back on other circuit.
3. If system detects a problem, DTC is set.
4. ATC control module senses low voltage return on either circuit when a high voltage signal is expected.

When this DTC is set, all shifting will be disabled. If currently in AUTO, system will not allow any further adaptive events (slip corrections). SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).
2. Disconnect transfer case shift motor connector. Check connector terminals for damage or corrosion. If terminals are damaged or corroded, go to step 8. If terminals are not damaged or corroded, go to next step.
3. Check motor/encoder for an internal open. If an internal open is found, go to step 7. If no open is found, go to next step.
4. Disconnect ATC control module connectors C1 and C2. Measure resistance of Black wire between control module connector C2 terminal "A" and motor/encoder connector. (Scheme 3)and (Scheme 6). If resistance is 0-2 ohms, go to next step. If resistance is more than 2 ohms, go to step 9.
5. Measure resistance of Red wire between control module connector C2 terminal "B" and motor/encoder connector. (Scheme 3)and (Scheme 6). If resistance is 0-2 ohms, go to next step. If resistance is more than 2 ohms, go to step 10.
6. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 11.
7. Replace transfer case motor/encoder. See «MOTOR/ENCODER»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 11.
8. Repair harness connector. When repair is complete, go to step 11.
9. Repair open in Black wire. When repair is complete, go to step 11.
10. Repair open in Red wire. When repair is complete, go to step 11.
11. Turn ignition off. Reconnect all disconnected components. Go to next step.
12. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).

Transfer case shift motor is a bi-directional, permanent magnet, DC motor. Transfer case, when energized, shift motor, through a series of gears, rotates a shaft which moves mode and range forks to shift transfer case ranges. DTC C0315 detects an open ground circuit.

System will test motor circuits as follows

1. System checks for unwanted voltage.
2. System supplies voltage on one circuit and reads voltage back on other circuit.
3. After system checks for opens and shorts on motor circuits, it applies voltage to motor and to ground circuit.
4. If system detects a high voltage return on ground circuit, DTC is set.
5. ATC control module senses high voltage return on ground circuit when low voltage signal is expected.

When this DTC is set, all shifting and clutch activation will be disabled. SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Disconnect ATC control module connector C2. Measure resistance of Black wire between ground and control module connector C2, terminal "C". If resistance is less than .5 ohm, go to step 4 . If resistance is more than .5 ohm, go to next step.
3. Locate and repair open or loose connection in Black wire. When repair is complete, go to step 5 .
4. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 5 .
5. Turn ignition off. Reconnect all disconnected components. When repair is complete, go to next step.
6. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

ATC control module controls transfer case brake control solenoid. Solenoid is energized (locking action released) during gear shifts and in AUTO mode. When power or ground is removed from solenoid (locking action applied), transfer case motor is prevented from moving. System is capable of proving 4H and 4L lockup without additional vehicle power to hold transfer case in these positions. This DTC detects an open solenoid coil, open circuit and/or open feed to solenoid.

System will set DTC under these conditions

1. System will try to turn solenoid off by opening ground circuit.
2. If control module is unable to de-energize solenoid, system will not attempt to de-energize solenoid again during that ignition cycle.
3. Auto transfer case solenoid output is detected as a low voltage when a high voltage is expected.

When this DTC is set, all shifting will be disabled. SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Disconnect transfer case connectors. Turn ignition on. Measure voltage of Orange wire between terminal "C" at transfer case connector and ground. If voltage is 9-14 volts, go to step 4 . If voltage is not 9-14 volts, go to next step.
3. Locate and repair open in Orange wire between transfer case and splice S236 in wiring harness, located near steering column harness at bulkhead, at left rear of engine compartment. When repair is complete, go to step 11 .
4. Measure resistance between Orange and Tan wire terminals at transfer case connector. See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) . If resistance is 20-80 ohms, go to next step. If resistance is not 20-80 ohms, go to step 7 .
5. Turn ignition off. Disconnect ATC control module connector C1 and C2. Measure resistance of Tan wire between ground and transfer case connector terminal E1. If resistance is less than infinite, go to step 8 . If resistance is infinite, go to next step.
6. Disconnect transfer case motor/encoder connector. Measure resistance of Tan wire between ground and motor/encoder connector and transfer case connector terminal E1. If resistance is 0-2 ohms, go to step 10 . If resistance is more than 2 ohms, go to step 9 .
7. Replace transfer case motor/encoder. See «MOTOR/ENCODER»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 11 .
8. Locate and repair short to ground in Tan wire between transfer case and ATC control module connectors. When repair is complete, go to step 11 .
9. Locate and repair open in Tan wire between transfer case and ATC control module connectors. When repair is complete, go to step 11 .
10. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
11. Turn ignition off. Reconnect all disconnected components. Go to next step.
12. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

ATC control module controls transfer case brake control solenoid. Solenoid is energized (locking action released) during gear shifts and in AUTO mode. When power or ground is removed from solenoid (locking action applied), transfer case motor is prevented from moving. System is capable of proving 4H and 4L lockup without additional vehicle power to hold transfer case in these positions. This DTC detects a shorted solenoid coil and/or shorted circuit.

System will set DTC when auto transfer case solenoid output is detected as a high voltage when low voltage is expected.

When this DTC is set, system will try to turn solenoid on (grounding the circuit). If system cannot energize solenoid, system will not attempt to energize solenoid again during that ignition cycle. All shifting will be disabled. SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Disconnect motor/encoder connector. Measure resistance between Tan and Orange wires at motor connector. If resistance is 20-80 ohms, go to next step. If resistance is not 20-80 ohms, go to step 4 .
3. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Turn ignition on. Measure voltage of Tan wire between control module connector C1, terminal E1 and ground. If voltage is zero volts, go to step 5 . If voltage is more than zero volts, go to step 6 .
4. Replace transfer case motor/encoder. See «MOTOR/ENCODER»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 7 .
5. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 7 .
6. Locate and repair short to voltage in Tan wire circuit between ATC control module and transfer case connectors. When repair is complete, go to step.
7. Turn ignition off. Reconnect all disconnected components. Go to next step.
8. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

Transfer case encoder is a switch that converts a shaft position, representing a range or mode position, into electrical signal inputs to ATC control module. Encoder houses 4 Hall Effect sensors used for channels "A", "B", "C" and "P". These sensors provide a path to ground when a magnet (part of shift rail) passes over them. ATC control module supplies an 8-volt reference and a ground circuit to encoder hall effect sensors on the Light Green/Black wire circuit and Black/White wire circuit. ATC control module supplies 5-volt signal on all channels. As these channels are pulled to ground, ATC control module can interpret location of transfer case shift position.

This DTC detects an open, short to ground or a short to voltage condition in encoders channel circuits.

System will set DTC when ATC control module senses all high or low voltage on encoder channel circuits.

When this DTC is set, all motor activity will stop and transfer case lock (brake control solenoid) is engaged. A default rail-to-rail shift may be allowed (toggle between 4H and 2H). SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).
2. Turn ignition off. Connect scan tool to DLC. Turn ignition on. Using scan tool, monitor states of Encoder Circuits "A", "B", "C" and "P". If all circuits display OFF, go to step 5. If all circuits do not display OFF, go to next step.
3. Disconnect ATC control module connectors C1 and C2. Measure resistance of suspect encoder circuit from previous step. See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246). If resistance is infinite, go to step 21. If resistance is less than infinite, go to next step.
4. Repair short to ground in suspect circuit. When repair is complete, go to step 22.
5. Measure voltage between Light Green/Black and Black/White wire terminals of control module connector C1. If voltage is 7-9 volts, go to next step. If voltage is not 7-9 volts, go to step 13.
6. Using scan tool, monitor states of Encoder Circuits "A", "B", "C" and "P". Individually jumper motor/encoder terminals "B", "C", "D" and "F" to terminal "A". (Scheme 6) If scan tool displays more than one circuit ON at the same time, go to step 10. If more than one circuit is not ON at the same time, go to next step.
7. If all circuits display ON when individually jumpered in previous step, go to step 11. If all circuits are not ON, go to next step.
8. Identify which circuit remained OFF in previous step. Disconnect ATC control module connectors C1 and C2. Measure resistance across suspect circuit. See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246). If resistance is 0-2 ohms, go to step 21. If resistance is more than 2 ohms, go to next step.
9. Repair open in suspect wire. When repair is complete, go to step 22.
10. Repair short between wires that were ON in step 6. When repair is complete, go to step 22.
11. Measure voltage between motor/encoder terminals "B", "C", "D" and "F" and terminal "A". (Scheme 6) If voltage is 4.8-5.1 volts, go to next step. If voltage is not 4.8-5.1 volts, go to step 21.
12. Replace motor/encoder. See «MOTOR/ENCODER»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 22.
13. If voltage measured in step 5 was more than 9 volts, go to next step. If voltage measure was not more than 9 volts, go to step 15.
14. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Turn ignition on. Measure voltage of Light Green/Black wire between motor/encoder connector and ground. If voltage is less than.5 volt, go to step 21. If voltage is more than.5 volt, go to step 17.
15. Measure resistance of Black/White wire between motor/encoder connector and ground. If resistance is less than 2 ohms, go to next step. If resistance is more than 2 ohms, go to step 18.
16. Disconnect ATC control module connectors C1 and C2. Measure resistance of Light Green/Black wire between control module connector C1, terminal F13 and motor/encoder connector. If resistance is less than 2 ohms, go to step 22. If resistance is more than 2 ohms, go to step 20.
17. Locate and repair short to power in Light Green/Black wire between ATC control module and motor/encoder connector. When repair is complete, go to step 22.
18. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Measure resistance of Black/White wire between control module connector C1, terminal F12 and motor/encoder connector. If resistance is less than 2 ohms, go to step 21. If resistance is more than 2 ohms, go to next step.
19. Locate and repair open in Black/White wire circuit between ATC control module and motor/encoder connectors. When repair is complete, go to step 22.
20. Repair open in Light Green/Black wire between ATC control module and motor/encoder connectors. When repair is complete, go to step 22.
21. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. Go to next step.
22. Turn ignition off. Reconnect all disconnected connectors. Go to next step.
23. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).

Park/Neutral switch supplies a 12-volt input to ATC control module when vehicle is in Park. Control module uses this input to confirm vehicle is in Park or Neutral. If vehicle is in Park, control module will not allow a range shift from 2H, 4H or AUTO to 4L range.

This DTC detects a voltage on Light Green wire circuit at ATC control module when control module sees a front or rear drive shaft speed signal, or vehicle speed from VCM or PCM over Class 2 data bus.

System will set DTC when ATC control module detects voltage in circuit, sees a front or rear drive shaft speed signal, or vehicle speed signal from VCM or PCM over Class 2 data bus is 10 MPH or more for 10 consecutive seconds.

Whenever Park/Neutral is detected, control module input indicates transmission was in Park. All range shifts will be disabled. SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Disconnect Park/Neutral position switch connector. Using scan tool, read Park Switch states. If scan tool indicates an open switch, go to step 4 . If scan tool does not indicate open switch, go to next step.
3. Replace Park/Neutral position switch. When replacement is complete, go to step 7 .
4. Disconnect ATC control module connectors C1 and C2. Turn ignition on. Measure voltage of Light Green wire between control module connector C1, terminal F15 and ground. If voltage is .5 volt or less, go to next step. If voltage is more than .5 volt go to step 6 .
5. Repair short to voltage in Light Green wire. When repair is complete, go to step 7 .
6. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
7. Turn ignition off. Reconnect all disconnected connectors. Go to next step.
8. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

The 4L discrete output circuit is used to notify VCM/PCM that vehicle is in 4WD low range (4L). VCM/PCM supplies 12 volts on this circuit. ATC control module supplies ground on this circuit when in 4L range. This DTC detects an ATC control module problem or short to voltage on Gray/Black wire circuit.

System will set DTC after system turns output on (grounds circuit) and detects a high voltage. System will not attempt this again during ignition cycle. ATC control module detects a high voltage when low voltage is expected on 4L discrete output (Gray/Black wire circuit). This condition may affect transmission shift points. SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Disconnect front axle switch connector. Turn ignition on. Measure voltage of Gray/Black wire between axle switch connector and ground. If voltage is .5 volt or less, go to step 4 . If voltage is more than .5 volt, go to next step.
3. Replace front axle switch. When repair is complete, go to step 7 .
4. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Measure voltage of Gray/Black wire between axle switch connector and ground. If voltage is .5 volt or less, go to next step. If voltage is more than .5 volt, go to step 6 .
5. Locate and repair short to voltage in Gray/Black wire. When repair is complete, go to step 7 .
6. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When replacement is complete, go to next step.
7. Turn ignition off. Reconnect all disconnected components. Go to next step.
8. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

ATC control module controls engagement and disengagement of front axle by grounding Gray/Black wire circuit from ATC control module to front axle actuator. Front axle is disengaged in 2H and Neutral only and should be engaged in all other modes. This DTC detects shorted actuator or a short to voltage on the circuit.

System will set DTC after trying to engage front axle. If engagement is not accomplished, system will not attempt this again during ignition cycle. ATC control module detects front axle output as a high voltage when low voltage is expected.

Under this condition, all shifting for 4WD and AUTO mode will be disabled. SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Connect scan tool to DLC. Turn ignition to run position (engine off). Using scan tool, record all freeze frame and failure records. Turn ignition off. Disconnect front axle actuator connector. Turn ignition to run position (engine off). Connect test light between ground and Gray/Black wire terminal at actuator connector. If test light is on, go to next step. If test light is off, go to step 4 .
3. Turn ignition off. Disconnect ATC control module connectors C1 and C2. Turn ignition to run position (engine off). Connect test light between ground and Gary/Black wire terminal at actuator connector. If test light is on, go to step 5 . If test light is off, go to step 6 .
4. Replace front axle actuator. When replacement is completed, go to step 7 .
5. Locate and repair short to voltage in Black/White wire circuit. When repair is complete, go to step 7 .
6. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When replacement is complete, go to next step.
7. Turn ignition off. Reconnect all disconnected components. Go to next step.
8. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

During a general system malfunction, ATC control module senses rear wheel to front wheel slip (difference of rear wheel to front wheel speed). Control module attempts to correct difference by turning on shift motor (internal to transfer case) to apply torque to front wheels.

System will set DTC after ATC control module is unable to correct sensed slip for 10 consecutive seconds.

Note. If DTC C0300 or C0305 is also present, repair those codes first.

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Place transmission in "P" position. Turn ignition on. Using scan tool, command Motor/Encoder circuit "A" and "B" ON. If motor/encoder turns on (buzzing noise), go to step 5 . If motor does not turn on, go to next step.
3. Turn ignition off. Disconnect motor/encoder connector. Turn ignition on. Check for DTC. If DTC C0310 is set, go to step 7 . If DTC C0310 is not set, go to next step.
4. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When replacement is complete, go to step 8 .
5. Use scan tool to manually command gear position by using ATC Mode Switch function. Use increase and decrease buttons to command all Mode Switch states while watching Encoder Gear Position. If Encoder Gear Position changes as commanded by scan tool, go to next step. If Encoder Gear Position does not change, go to step 7 .
6. Overhaul transfer case as required. See NEW VENTURE 246 OVERHAUL article. When repair is complete, go to step 8 .
7. Replace motor/encoder. See «MOTOR/ENCODER»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
8. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

Front and rear drive shaft speed sensors are a permanent magnet generator, producing AC voltage pulses. AC voltage level and number of pulses increases as speed increases. ATC control module converts pulsating AC voltage to drive shaft RPM which is used for calculations. Control module uses these inputs when vehicle is in 4H, 4L and AUTO ranges only. Drive shaft RPM can be displayed using scan tool. This DTC detects a difference in speed sensor inputs of more than 20 percent.

System will set DTC when ATC control module detects continued readings of front and rear drive shaft RPM signals that do not match. Control module cannot determine drive shaft speed.

System will set this DTC if front and rear drive shaft inputs indicate speed of less than 20 percent difference for 40 seconds when the following conditions exists

1. Transmission is not in Park or Neutral.
2. Engine is running.
3. Front axle is engaged.
4. Front drive shaft indicates speed less than 75 MPH.
5. Front or rear drive shaft speed exceeds 512 RPM.
6. Vehicle speed on Class 2 Data Bus exceeds 10 MPH.

This condition will disable all shifts to AUTO mode. System will not allow any further adaptive events (slip correction). SERVICE 4WD light will be on for remainder of current ignition cycle.

1. If DTC C0300 is also present, diagnose this DTC prior to diagnosing DTC C0376. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition off. Inspect front and rear axle ratios and tires for mismatch. Check for missing or disconnected drive shaft. Confirm speed sensors are mounted in proper positions. Inspect all connectors for clean and solid connections. If any problem was found, go to step 6 . If no problem was found, go to next step.
3. Turn ignition off. Connect scan tool. Turn ignition on. Check for powertrain DTCs. If any vehicle speed DTC is found, go to appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. If no vehicle speed DTC is present, go to next step.
4. Drive vehicle while observing ATC Data List on scan tool. Note value of rear drive shaft speed. Change scan tool to Transmission Data List. Observe output shaft speed. If RPM values are about the same, go to next step. If RPM values are not about the same, go to step 7 .
5. Using scan tool while observing ATC Data List, compare rear drive shaft speed with front drive shaft speed. If RPM values are about the same, go to step 8 . If RPM values are not about the same, go to step 9 .
6. Repair or replace connectors and/or terminals as needed. When replacement is complete, go to step 10 .
7. Replace transfer case rear vehicle speed sensor. When repair is complete, go to step 10 .
8. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When replacement is complete, go to step 10 .
9. Inspect front transfer case speed sensor reluctor wheel for damage, misalignment and slipping. When repairs are complete, go to next step.
10. Turn ignition off. Reconnect all disconnected components. Go to next step.
11. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

DTC C0387: UNABLE TO PERFORM SHIFT

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Connect scan tool. Select transfer case. Turn ignition on. Using scan tool, command tool through all shift modes while monitoring Encoder Circuits "A", "B", "C" and "P". If all encoder circuits change between ON and OFF, go to next step. If all circuits do not change between ON and OFF, go to step 4 .
3. Turn ignition off. Remove encoder motor. Use a wrench on end of sector shaft and turn shaft. If shaft binds, go to step 9 . If shaft does not bind, go to step 10 .
4. If any encoder circuits change states, go to next step. If no encoder circuits change states, go to step 8 .
5. Identify which encoder circuit does not change state. Disconnect ATC control module connectors C1 and C2. Disconnect motor/encoder connectors C1 and C2. Measure resistance in circuits which did not change states. See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) . If resistance is 0-2 ohms, go to next step. If resistance is more than 2 ohms, go to step 11 .
6. Measure resistance in circuits that did not change states. If resistance is infinite, go to next step. If resistance is less than infinite, go to step 12 .
7. Turn ignition on. Measure voltage of circuits that did not change states. If voltage is zero volts, go to step 14 . If voltage is more than zero volts, go to step 13 .
8. Turn ignition off. Remove encoder motor. Use a wrench on end of sector shaft and turn shaft. If shaft binds, go to next step. If shaft does not bind, go to step 14 .
9. Repair mechanical problem in transfer case. See NEW VENTURE 246 OVERHAUL article. When repair is complete, go to step 15 .
10. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 15 .
11. Repair open in suspect circuit. When repair is complete, go to step 15 .
12. Repair short to ground in suspect circuit. When repair is complete, go to step 15 .
13. Repair short to voltage in suspect circuit. When repair is complete, go to step 15 .
14. Replace transfer case motor/encoder. See «MOTOR/ENCODER»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
15. Turn ignition off. Reconnect all disconnected components. Go to next step.
16. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

At each power up, ATC control module runs a self-test on following items

1. EEPROM Checksum
2. ROM Checksum
3. RAM Checksum
4. RAM Malfunction
5. Relay Malfunction

System will set DTC when the following conditions are recognized

1. Critical operational parameters stored in EEPROM have failed checksum test, indicating invalid data.
2. Masked ROM code has failed checksum test, indicating masked ROM data is no longer valid.
3. ROM code has failed checksum test, indicating ROM data is no longer valid.
4. One or more RAM locations have failed operational test, indicating some portions of RAM are not functional.
5. Motor circuit test has indicated one of the control module relays is not able to make contact.

When this DTC occurs, SERVICE 4WD light will be on and system will be disabled. To repair this DTC, replace ATC control module, then perform TRANSFER CASE SYSTEM CHECK .

ATC control module uses VIN information for calculations required for different vehicle calibrations, based on axle ratio, transmission, tire size and engine. System does not know which calibration to use without this data.

When this DTC is set, ignition counts since last fault will be cleared, system will be disabled until valid VIN data is received, and SERVICE 4WD light will be on.

System will set DTC if ATC control module does not receive valid VIN digit for correct vehicle application within 2 seconds after power up.

Possible Causes

Possible causes of this DTC include

1. Class 2 Data Bus malfunction.
2. VCM/PCM malfunction.
3. ATC control module installed in incorrect vehicle.

Ensure correct VIN number is received by ATC control module.

FRONT AXLE WILL NOT ENGAGE

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).
2. Turn ignition on. Using scan tool, read Front Axle Switch Status. Use scan tool to engage front axle. If scan tool display changes from UNLOCKED to LOCKED, go to step 6. If display does not change, go to next step.
3. Turn ignition off. Disconnect front axle switch connector. Turn ignition on. Measure voltage between Brown and Black wire terminals at axle switch connector. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, go to step 9.
4. Connect voltmeter between Brown and Gray/Black wire terminals at axle switch connector. Use scan tool to engage front axle and read voltage specifications. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, go to step 14.
5. With scan tool stilled hooked up, connect jumper wire between Brown and Black/White terminals of axle switch connector. Read Front Axle Switch status on scan tool. If status shows front axle LOCKED, go to step 17). If status does not show LOCKED, go to step 7.
6. Inspect front axle for mechanical problems. If no mechanical problems are found, replace front axle switch. When repair is complete, go to step 19.
7. Disconnect ATC control module connectors C1 and C2. Measure resistance of Black/White wire between control module connector C1, terminal E14 and front axle switch connector terminal "A". (Scheme 2)and (Scheme 8).
8. Repair open in Black/White wire. When repair is complete, go to step 19.
9. Measure voltage of Brown wire between front axle switch connector and ground. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, go to step 11.
10. Replace front axle switch. When repair is complete, go to step 19.
11. Inspect 4WD fuse in power distribution box. If fuse is okay, go to next step. If fuse is blown, go to step 13.
12. Repair open in Brown wire. When repair is complete, go to step 19.
13. Replace 4WD fuse. Turn ignition on. Wait 2 minutes, then check fuse. If fuse is okay, go to step 19. If fuse is blown, go to step 18.
14. Disconnect ATC control module connectors C1 and C2. Measure resistance of Gray/Black wire between control module connector C1, terminal F4 and axle switch connector. (Scheme 2)and (Scheme 8). If resistance is 0-2 ohms, go to step 16. If resistance is not 0-2 ohms, go to next step.
15. Repair open in Gray/Black wire. When repair is complete, go to step 19.
16. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 19.
17. Replace front axle switch. When repair is complete, go to step 19.
18. Repair short to ground in Brown wire. When repair is complete, go to next step.
19. Turn ignition off. Reconnect all disconnected components. When repair is complete, go to next step.
20. Clear all DTCs, then perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).

FRONT AXLE WILL NOT DISENGAGE

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).
2. Turn ignition on. Place vehicle in 2WD mode. Using scan tool, read Front Axle Switch Status. If scan tool display shows LOCKED, go to step 6. If display does not show LOCKED, go to next step.
3. Turn ignition off. Disconnect front axle switch connector. Turn ignition on. measure voltage between Brown and Black wire terminals of axle switch connector. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, go to step 12.
4. Connect voltmeter between Brown and Gray/Black wire terminals of axle switch connector. Use scan tool to engage front axle. Read voltage. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, go to step 17.
5. Connect jumper wire between Black/White and brown wire terminals of axle switch connector. Use scan tool to read front axle switch status. If status shows LOCKED, go to step 20. If status does not show LOCKED, go to step 10.
6. Disconnect front axle switch connector. Use scan tool to read front axle switch status. If status shows LOCKED, go to step 8. If status does not show LOCKED, go to next step.
7. Check for mechanical problems. If no problem is found, replace front axle switch. When repair is complete, go to step 22.
8. Measure voltage between Black/White and Black wire terminals of axle switch connector. If voltage is.5 volt or less, go to step 19. If voltage is more than.5 volt, go to next step.
9. Repair short to voltage in Black/White wire. When repair is complete, go to step 22.
10. Disconnect ATC control module connectors C1 and C2. Measure resistance of Black/White wire between control module connector C1, terminal E14 and axle switch connector. (Scheme 2)and (Scheme 8). If resistance is 0-2 ohms, go to step 19. If resistance is more than 2 ohms, go to next step.
11. Repair open in Black/White wire. When repair is complete, go to step 22.
12. Measure voltage of Brown wire between front axle switch connector and ground. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, go to step 14.
13. Replace front axle switch. When repair is complete, go to step 22.
14. Inspect 4WD fuse in power distribution box. If fuse is okay, go to next step. If fuse is blown, go to step 16.
15. Repair open in Brown wire. When repair is complete, go to step 22.
16. Replace 4WD fuse. Turn ignition on and wait 2 minutes. Check fuse. If fuse is blown, go to step 21). If fuse is okay, go to step 22.
17. Disconnect ATC control module connectors C1 and C2. Measure resistance of Gray/Black wire between control module connector C1, terminal F4 and axle switch connector. (Scheme 2)and (Scheme 8).
18. Repair open in Gray/Black wire. When repair is complete, go to step 22.
19. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 22.
20. Replace front axle switch. When repair is complete, go to step 22.
21. Repair short to ground in Brown wire. When repair is complete, go to next step.
22. Turn ignition off. Reconnect all disconnected components. Go to next step.
23. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check).

SELECT SWITCH INOPERATIVE

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Connect scan tool to DLC. Turn ignition on. Place transmission in neutral, or depress clutch pedal on manual transmission models. Using scan tool, in Commanded Mode Indicator state, depress each select switch button. If indicator state changes when select switch buttons are pressed, go to step 5 . If states do not change, go to next step.
3. Using scan tool, command through all ranges of select switch. Observe Commanded Mode Indicator states. If indicator states change, go to step 5 . If indicator states do not change, go to next step.
4. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 6 .
5. Replace transfer case select switch. See «TRANSFER CASE SELECT SWITCH»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
6. Turn ignition off. Reconnect all disconnected components. Go to next step.
7. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

NO CORRECTION FOR SLIP IN AWD (AUTO) MODE

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Connect scan tool to DLC. Turn ignition on. Place vehicle in 4WD mode. Using scan tool, read front axle switch status. If front axle is LOCKED, go to next step. If front axle is not LOCKED, go to «FRONT AXLE WILL NOT ENGAGE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__front-axle-will-not-engage) test.
3. Change scan tool to AWD mode. Read front axle switch status. If front axle still displays LOCKED, go to next step. If front axle does not display LOCKED, go to step 6 .
4. Change scan tool back to 4WD mode. Drive vehicle a short distance while observing ATC Data List on scan tool. Note values for front and rear drive shaft speeds at same set speed. If RPM values are about the same. go to step 6 . If RPM values are not about the same, go to next step.
5. Inspect front axle and transfer case for mechanical failure. Repair or replace as needed. When repairs are complete, go to step 7 .
6. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
7. Turn ignition off. Reconnect all disconnected components. Go to next step.
8. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

1 OR MORE SELECT SWITCH INDICATOR LIGHTS DO NOT LIGHT

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Connect scan tool. Turn ignition on. Using scan tool, command each indicator light ON. If all lights turn on, go to step 7 . if all lights do not turn on, go to next step.
3. Using scan tool, view ATC Data List. Command each indicator light ON. If each light changes from OFF to ON as commanded, go to step 7 . If light(s) does not turn from OFF to ON, go to next step.
4. Disconnect ATC control module connectors C1 and C2. Connect a fused jumper wire between ground and each indicator light circuit. See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) . If all lights turn on when grounded, go to step 7 . If light(s) does not come on, go to next step.
5. Measure voltage of suspect light circuit between light connector and ground. See «WIRING DIAGRAMS»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) . If voltage is 9-14 volts, go to step 8 . If voltage is not 9-14 volts, go to next step.
6. Check suspect light circuit for open. If an open if found, go to step 9 . If no opens are found, go to step 8 .
7. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 10 .
8. Replace select switch. See «TRANSFER CASE SELECT SWITCH»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 10 .
9. Repair open in suspect light circuit. When repair is complete, go to next step.
10. Turn ignition off. Reconnect all disconnected components. Go to next step.
11. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

2 OR MORE SELECT SWITCH INDICATOR LIGHTS REMAIN ON

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Connect scan tool to DLC. Turn ignition on. Using scan tool, command all lights off. If all lights go off, go to next step. If all lights do not go off, go to step 4 .
3. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 9 .
4. Using scan tool, determine which mode transfer case is in. Use this information to determine which indicator is faulty. Disconnect select switch connectors. Measure resistance of suspect indicator light wire between select switch connector and ground. If resistance is infinite, go to step 7 . If resistance is less than infinite, go to next step.
5. Disconnect ATC control module connectors C1 and C2. Measure resistance of suspect indicator light wire between select switch connector and ground. If resistance is infinite, go to step 8 . If resistance is less than infinite, go to next step.
6. Repair short to ground in suspect wire. When repair is complete, go to step 9 .
7. Replace select switch. See «TRANSFER CASE SELECT SWITCH»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 9 .
8. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
9. Turn ignition off. Reconnect all disconnected connectors. Go to next step.
10. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

SERVICE 4WD LIGHT STAYS ON WHEN KEY IS ON

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Connect scan tool to DLC. Turn ignition on. Using scan tool, command SERVICE 4WD light off. If light goes off, go to step 7 . If light does not go off, go to next step.
3. Disconnect ATC control module connectors C1 and C2. If SERVICE 4WD indicator goes off, go to step 7 . If indicator does not go off, go to next step.
4. Disconnect instrument cluster connector. Measure resistance of Light Blue/Black wire between instrument cluster connector and ground. If resistance is infinite, go to next step. If resistance is less than infinite, go to step 6 .
5. Repair instrument cluster for short to ground. When repair is complete, go to step 8 .
6. Repair short to ground in Light Blue/Black wire. When repair is complete, go to step 8 .
7. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
8. Turn ignition off. Reconnect all disconnected connectors. Go to next step.
9. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

SWITCH INDICATOR LIGHTS FLASH CONTINUOUSLY

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Turn ignition on. Connect scan tool to DLC. Using scan tool, check front axle status. If front axle is LOCKED, go to step 6 . If front axle is not locked, go to next step.
3. Using scan tool, determine if front axle is in AUTO, 4WD HI or 4WD LO. If axle is in any of these positions, go to next step. If front axle is in none of these positions, go to step 13 .
4. Disconnect ATC control module connectors C1 and C2. Turn ignition on. Measure voltage of Gray/Black or Light Blue wire between control module connector C1 and ground. If voltage is 9-14 volts, go to step 13 . If voltage is not 9-14 volts, go to next step.
5. Disconnect front axle switch connector. Measure resistance of Gray/Black or Light Blue wire between control module connector C1, terminal F4 and axle switch connector. If resistance is 0-2 ohms, go to step 14 . If resistance is more than 2 ohms, go to step 11 .
6. Using scan tool, determine if axle is in 2WD position, If axle is in 2WD, go to next step. If axle is not in 2WD, go to step 13 .
7. Measure voltage of Black/White wire between control module connector C1, terminal E14 and ground. If voltage is zero volts, go to step 13 . If voltage is more than zero volts, go to next step.
8. Measure voltage of Black/White wire between front axle switch connector and ground. If voltage is zero volts, go to next step. If voltage is more than zero volts, go to step 12 .
9. Inspect front axle assembly for mechanical problems. If mechanical problems exist, go to next step. If no problems are found, go to step 14 .
10. Repair front axle mechanical problem. When repair is complete, go to step 16 .
11. Repair open in Gray/Black or Light Blue wire. When repair is complete, go to step 16 .
12. Repair short to voltage in Black/White wire. When repair is complete, go to step 16
13. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 16 .
14. Replace front axle switch. See «TRANSFER CASE SELECT SWITCH»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to step 16 .
15. Replace front drive axle clutch solenoid. When repair is complete, go to next step.
16. Turn ignition off. Reconnect all disconnected connectors. Go to next step.
17. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

SERVICE 4WD INDICATOR DOES NOT LIGHT

1. If TRANSFER CASE SYSTEM CHECK was performed, go to next step. If system check was not performed, see «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .
2. Connect scan tool to DLC. Turn ignition on. Using scan tool, command SERVICE 4WD indicator ON. If indicator turns on, go to step 11 . If indicator does not turn on, go to next step.
3. Disconnect ATC control module connectors C1 and C2. Connect fused jumper on Light Blue/Black wire between control module connector C1, terminal E2 and ground. If SERVICE 4WD indicator turns on, go to step 11 . If indicator does not turn on, go to next step.
4. Disconnect instrument cluster connector. Measure resistance of Light Blue/Black wire between instrument cluster connector and control module connector C1, terminal E2. If resistance is 0-2 ohms, go to next step. If resistance is not 0-2 ohms, go to step 8 .
5. Turn ignition on. Measure voltage of Pink wire between instrument cluster connector and ground. If voltage is 9-14 volts, go to next step. If voltage is not 9-14 volts, go to step 9 .
6. Check SERVICE 4WD light bulb for failure. If bulb is faulty, go to step 10 . If bulb is okay, go to next step.
7. Repair instrument cluster for open. When repair is complete, go to step 12 .
8. Repair open in Light Blue/Black wire. When repair is complete, go to step 12 .
9. Repair open in Pink wire. When repair is complete, go to step 12 .
10. Replace indicator bulb. When repair is complete, go to step 12 .
11. Replace ATC control module. See «ATC CONTROL MODULE»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246) under REMOVAL & INSTALLATION. When repair is complete, go to next step.
12. Turn ignition off. Reconnect all disconnected components. Go to next step.
13. Clear all DTCs. Perform «TRANSFER CASE SYSTEM CHECK»(/cadillac/escalade/gmt400-1998-2000/remont/transfer-case/#transfer-case-diagnosis-new-venture-246__transfer-case-system-check) .

Removal & Installation

Disconnect negative battery cable. Remove transfer case shield. Remove wiring harness connector from motor/encoder. Remove 3 retaining bolts and remove motor/encoder. (Scheme 11) To install, reverse removal procedure, using NEW gasket. Align mating surface detents of motor/encoder and transfer case. Tighten bolts to 18 ft. lbs. (24 N.m).

Scheme 11

Disconnect negative battery cable. Remove select switch from instrument panel by pulling tabs on rear of switch inward, then pulling switch straight out. Disconnect electrical connector. To install, reverse removal procedure.

Disconnect negative battery cable. Remove lower instrument panel trim. Control module is mounted to steering column bracket. On both transfer cases, remove 2 screws holding control module to bracket (mounted on instrument panel reinforcement). Remove electrical connectors and remove control module. To install, reverse removal procedure. (Scheme 12) Tighten screws to 71 INCH lbs. (8 N.m).

Scheme 12

Disconnect negative battery cable. Remove electrical connector(s) from speed sensor(s). Unscrew and remove sensor(s) from transfer case. To install, reverse removal procedure. (Scheme 1)

NV246 Transfer Case Wiring Diagram (Escalade, Suburban, Tahoe & Yukon With Auto-Trac 4WD). Scheme 13

See also:
• SELECT SWITCH INOPERATIVE
• ONE OR MORE SELECT SWITCH INDICATOR LIGHTS DO NOT LIGHT
• DIAGNOSTIC TROUBLE CODE DEFINITIONS
• SERVICE 4WD INDICATOR DOES NOT LIGHT
• C0387
• TRANSFER CASE SYSTEM CHECK
• FRONT AXLE WILL NOT ENGAGE