Circuit/System Testing

WARNING: This page is about a different car, the 2018 GMC Yukon XL, 2018 GMC Yukon, 2018 Chevrolet Tahoe, and 2018 Chevrolet Suburban. However, it is still accessible from the selected car via links, so may be relevant.

Ignition OFF, disconnect the harness connector at the M26 front axle engagement actuator.
Ignition ON, engine OFF.
Test for a True B+ (+0.0/-1.0 V) between the ignition 1 voltage circuit terminal 1 and a good ground, such as the ground terminal of the EL-49742 harness, black terminal.
NOTE:
- When test probing harness terminals, it is imperative to use the proper test probe from the most current version of the J-35616 GM-Approved Terminal Test Kit. Use of an improper test probe may deform the terminal, resulting in intermittent open conditions.
- Testing for steps 3 - 11 is performed on the M26 front axle engagement actuator harness connector using the BL probes J-35616-64B.
- If less than B+ (+0.0/-1.0 V)
1. Ignition OFF, remove the F40UA fuse, X50A fuse block - underhood.
  or
  
  Disconnect the X2 harness connector at the X50A fuse block - underhood.
2. Test for less than 10 Ω in the run/crank ignition 1 voltage circuit end to end.
  - If 10 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 10 Ω
3. Test for infinite resistance between the run/crank ignition 1 voltage circuit, terminal 1 and a good ground, such as the ground terminal of the EL-49742 harness, black terminal.
  - If less than infinite resistance, repair the short to ground condition in the circuit.
  - If greater than 10 Ω
4. Test for greater than 10 Ω between run/crank ignition 1 voltage circuit, terminal 1 and all other terminals of the M26 front axle engagement actuator.
  - If 10 Ω or less, repair the short together condition in the affected circuits.
  - If greater than 10 Ω
5. Ignition ON.
6. Test for a less than 1.0 V between the run/crank ignition 1 voltage circuit, terminal 1, and a good ground such as the ground terminal of the EL-49742 harness, black terminal.
  - If 1.0 V or greater, repair the short to voltage in the circuit.
  - If less than 1 V, replace the KR73 ignition main relay. Refer to X50A fuse block - underhood label.
- Go to next step: If B+ (+0.0/-1.0 V)
Ignition 1 voltage circuit OK.
Test for a true B+ (+0.0/-1.0 V) between the ground circuit, terminal 4, and the run/crank ignition 1 voltage circuit, terminal 1 or the B+ terminal of the EL-49742 harness, red terminal.
- If less than the B+ (+0.0/-1.0 V)
1. Ignition OFF, disconnect the grounding bolt G110. Refer to Ground Views .
2. Test for less than 10 Ω in the ground circuit end to end.
  - If 10 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 10 Ω
3. Test for infinite resistance between the ground circuit, terminal 4 and a good ground such as the ground terminal of the EL-49742 harness, black terminal.
  - If 10 Ω or less, repair the short to ground condition in the circuit.
  - If greater than 10 Ω
4. Test for infinite resistance between ground circuit, terminal 4 and all other terminals of the M26 front axle engagement actuator harness connector.
  - If 1 Ω or less, repair the short together condition in the affected circuits.
  - If greater than 1 Ω
5. Ignition ON.
6. Test for a less than 1.0 V between the ground circuit, terminal 4 and a good ground such as the ground terminal of the EL-49742 harness, black terminal.
  - If 1.0 V or greater, repair the short to voltage in the circuit.
  - If less than 1 V, clean the G110 grounding surface. Refer to Testing for Intermittent Conditions and Poor Connections .
- Go to next step: If B+
Ground circuit OK.
Test for a diagnostic B+ (+0.0/-1.0 V) between the four wheel drive wheel lock indicator circuit, terminal 3, and the run/crank ignition 1 voltage circuit, terminal 1 or the B+ terminal of the EL-49742 harness, red terminal.
- If less than B+ (+0.0/-1.0 V)
1. Ignition OFF, disconnect the X1 harness connector at the K69 transfer case control module.
2. Test for less than 10 Ω in four wheel drive wheel lock indicator circuit end to end.
  - If 10 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 10 Ω
3. Test for infinite resistance between the four wheel drive wheel lock indicator circuit, terminal 3 and a good ground such as the ground terminal of the EL-49742 harness, black terminal.
  - If less than infinite resistance, repair the short to ground condition in the circuit.
  - If greater than 10 Ω
4. Test for infinite resistance between four wheel drive wheel lock indicator circuit, terminal 3 and all other terminals of the M26 front axle engagement actuator harness connector.
  - If less than infinite resistance, repair the short together condition in the affected circuits.
  - If greater than 10 Ω
5. Ignition ON.
6. Test for a less than 1.0 V between the four wheel drive wheel lock indicator circuit, terminal 3 and a good ground such as the ground terminal of the EL-49742 harness, black terminal.
  - If 1.0 V or greater, repair the short to voltage in the circuit.
  - If less than 1 V, replace the K69 transfer case control module. Refer to Transfer Case Control Module Replacement .
- Go to next step: If B+
Four wheel drive wheel lock indicator circuit OK.
Test for 2.8 to 4.8 V between the test points:Front Axle Actuator Control & Chassis Ground
- If less than 2.8 V
1. Ignition OFF, disconnect the X1 harness connector at the K69 transfer case control module.
2. Test for less than 10 Ω in front axle actuator control circuit end to end.
  - If 10 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 10 Ω
3. Test for greater than 10 Ω between the front axle actuator control circuit, terminal 2 and a good ground such as the ground terminal of the EL-49742 harness, black terminal.
  - If 10 Ω or less, repair the short to ground condition in the circuit.
  - If greater than 10 Ω
4. Test for greater than 1 Ω between front axle actuator control circuit, terminal 2 and all other terminals of the M26 front axle engagement actuator harness connector.
  - If 1 Ω or less, repair the short together condition in the affected circuits.
  - If greater than 1 Ω
- If greater than 4.8 V
1. Ignition OFF, disconnect the X1 harness connector at the K69 transfer case control module.
2. Test for greater than 5 Ω between front axle actuator control circuit, terminal 2 and all other terminals of the M26 front axle engagement actuator harness connector.
  - If 5 Ω or less, repair the short together condition in the affected circuits.
  - If greater than 5 Ω
3. Ignition ON.
4. Test for a less than 1.0 V between the front axle actuator control circuit, terminal 2 and a good ground such as the ground terminal of the EL-49742 harness, black terminal.
  - If 1.0 V or greater, repair the short to voltage in the circuit.
  - If less than 1 V, replace the K69 transfer case control module. Refer to Transfer Case Control Module Replacement .
- Go to next step: If between 2.8 and 4.8 V
The run/crank ignition 1 voltage circuit, the front axle switch signal circuit, the front axle control circuit, the ground circuit, and the K69 transfer case control module are OK.