Hummer H1 (2006+). Manual - part 342

12-44

Electrical System

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Ignition Switch Replacement  (Figure 12-35)

Removal

1.

Remove the steering column covers.

2.

Remove the multi-function switch.

3.

Remove the screw and the interlock cable from the ignition switch (Figure 12-35).

4.

Remove the two cap screws and the ignition switch from the steering column.

Installation

1.

Apply thread-locking compound to the cap screw threads and install the ignition switch on the steering column with the two 
capscrews.

2.

Install the interlock cable on the ignition switch with screw.

3.

Install the multi-function switch.

4.

Install the steering column covers.

5.

Ensure the ignition switch operates properly.

When testing the ignition switch with the “Quick Test” make sure the test is performed with the harness disconnected. The termi-
nals to be checked will be on the ignition switch.

Ignition Switch Quick Test  (Figure 12-124)

Connect DVOM

Key Position

Values

Check between the two BATT termi-
nals.

Accessory, Lock, Off, Run, and Start.

Closed circuit in all 5 positions.

Between the BATT terminal and ST.

Accessory, Lock, Off, Run, and Start.

Closed in the Start position only.

Between the BATT terminal and A2.

Accessory, Lock, Off, Run, and Start.

Closed in the Run position only.

Between the BATT terminal and I1.

Accessory, Lock, Off, Run, and Start.

Closed in the Run position only.

Between the BATT terminal and I2.

Accessory, Lock, Off, Run, and Start.

Closed in the Start position only.

Between the BATT terminal and A1,

Accessory, Lock, Off, Run, and Start.

Closed in the Run and the 

Accessory position only.

Between terminal P1 and the Ignition 
switch case.

Accessory, Lock, Off, Run, and Start.

Closed in the Start position only.

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 Electrical System  12-45

IGNITION SWITCH INTERLOCK SYSTEM DESCRIPTION

The purpose of the ignition interlock is to prevent the driver from turning the ignition to the lock position while the vehicle is in
any gear other than park. When the shifter is removed from the park position, voltage from the interlock switch energizes the igni-
tion interlock solenoid and pulls the cable, stoping the ignition from being turned to the lock position. If electrical power is lost due
to a dead battery or system failure, the solenoid defaults to the open position. With the ignition interlock solenoid in the open posi-
tion the ignition can be turned to the lock position.

 Ignition Switch Interlock inoperative  (Figure 12-141)

STEP

ACTION

VALUES

YES

NO

1.

Does the brake shift interlock work properly?

Go to step 2.

Go to brake shift 

interlock inopera-

tive

2.

With the ignition switch in the “run” position 
using a DVOM check for voltage at fuse 6 E.
Is the specified voltage present? 

 B+

Go to step 3.

Go to step 6

3.

With the ignition switch in the “run” position acti-
vate the park brake and place the shifter in the 
neutral position.
Using a DVOM check for voltage at the WH wire 
(CKT 1071) between pin A of the ignition inter-
lock solenoid connector and a good ground.
Is the specified voltage present? 

B+

Go to step 4.

Replace the 6 E 
fuse or repair the 
wire to the B3 as 
necessary.
Did you make the 
necessary
repairs?

4.

Using a DVOM check for voltage at the WH wire 
(CKT 1071) between pin A and the BK wire 
(CKT 1072) pin B of the ignition interlock sole-
noid connector.
Is the specified voltage present? 

B+

Replace the 

ignition inter-

lock solenoid

Go to step 5.

5.

Using a DVOM measure the resistance of the BK 
wire (CKT 1072) between pin B of the ignition 
interlock solenoid connector and pin D of the 
sifter assembly.
Is the resistance greater than the specified value?

.2 Ohms

Repair the high 

resistance in the 

(CKT 1072) 

between pin B 

of the ignition 

interlock sole-

noid connector 

and pin D of the 

sifter assembly

Replace the 

shifter assembly.

12-46

Electrical System

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BRAKE SHIFT INTERLOCK SYSTEM DESCRIPTION

The purpose of the brake shift interlock solenoid is to prevent a driver from engaging a transmission gear before the brakes are ap-
plied (Figure 12-35). When the brake pedal is depressed, voltage from the brake switch de-energizes the interlock solenoid. The
transmission shift lever can then be pulled out of the park position. If electrical power is lost due to a dead battery or system failure,
the solenoid defaults to the open position. With the brake/shift interlock solenoid in the open position the shifter may not be moved
out of the park position.

Figure 12-35:   Brake Shift Interlock Solenoid

 Brake Shift Interlock Inoperative  (Figure 12-141)

STEP

ACTION

VALUES

YES

NO

1

Gain access to the shifter assembly connector. 
Using a DVOM, check for the resistance on the 
LB wire (CKT 32) between pin B and a good 
ground.
Is the resistance greater than the specified value?

.2

1

Repair the open or bad 

connection in CKT 32 

between the interlock 

solenoid and G1.

Go to step 2.

2

With the ignition switch in the “run” position and 
the brake pedal depressed.
Check the voltage between the WH wire (CKT 
520) pin A of the shifter assembly connector and 
a good ground. 
Is the specified voltage present?

B+ 

Replace the shifter      

assembly.

 Go to step 3.

SOLENOID

INTERLOCK

SWITCH

INTERLOCK

LEVER

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 Electrical System  12-47

3

With the ignition switch in the “run” position and 
the brake pedal depressed.
Check the voltage between M8 cavity of the shift 
inter lock relay and a good ground. 
Is the specified voltage present?

B+

Repair the open or high 

resistance in the WH 

wire (CKT) 520 

between the shifter 

assembly connector and 

cavity M8 of the shift 

inter lock relay

Go to step 4.

4

With the ignition switch in the “run” position and 
the brake pedal depressed.
Check the voltage between L9/L7 cavity of the 
shift inter lock relay and a good ground.
Is the specified voltage present?

B+

Go to step 5.

Repair the open or 

high resistance in the 

RD  wire (CKT 1073) 

between the shift inter 

lock relay and buss 1 

A

5

With the ignition switch in the “run” position and 
the brake pedal depressed.
Check the voltage between M9 cavity of the shift 
inter lock relay and a good ground.
Is the specified voltage present?

B+

Replace the shift inter 

lock relay.

Go to step 6.

6

With the ignition switch in the “run” position and 
the brake pedal depressed.
Check the voltage between pin A of the brake 
switch and a good ground.
Is the specified voltage present?

B+

Repair the open or bad 

connection on CKT 1070 

between the shift inter 

lock relay brake switch.

Replace the brake 

switch.

 Brake Shift Interlock Inoperative  (Figure 12-141)

STEP

ACTION

VALUES

YES

NO