Hummer H1 Service Manual page 321

5-122 Transmission/Transfer Case
DTC P1875 Four-Wheel Drive Low Switch
Fault
Circuit Description
The 4WD low circuit consists of a 4WD indicator, switch, and
wiring. When the operator moves the shift lever to 4 Low, the
4WD indicator lamp will illuminate and circuit 784 voltage to
the PCM will change from B+ to zero. The 4WD low switch
signal is used to correct transmission output speed signal to
PCM. This signal is used to compensate for transfer case gear
reduction. The PCM uses the transmission output speed signal
to adjust shift points, line pressure, and converter clutch sched-
uling.
This DTC detects a continuous open or short to ground in the
4WD circuit.
FUSE 2D
20 AMP
INTERIOR
C33-J
C28-D13 C28-C13
C28-C12 C28-C11
C27-D2
BATTERY
TRANSFER
POSITIVE
CASE RANGE
SWITCH
___________________________________________
FUSE 3A FUSE 4D
20 AMP 15 AMP
EXTERIOR INTERIOR
A
BRAKE
LAMP
B
31
C1-
TO BRAKE
LAMP
C29-B10
IGNITION
BRAKE LIGHT
VOLTAGE
SWITCH SIGNAL
POWERTRAIN
CONTROL
MODULE (PCM)
Conditions For Setting DTC
• No DTCs P0121, P0122 or P0123.
• No DTC P0502.
• No 1-2 shift solenoid DTC P0753.
• No 2-3 shift solenoid DTC P0758.
• No DTC P1810.
• No PWM solenoid DTC P1860.
• Engine speed is greater than 400 rpm for 8 seconds.
• Gear range is D4.
• Throttle angle is between 10% and 100%.
• Transmission fluid temperature is between 18-125°C
(68°-248°F).
• Shift solenoid performance counters are zero.
All of the above conditions have been met and either one of the
following fail conditions are true.
• Four wheel drive low is stuck "on" for 2 seconds. Gear
ratio between 0.95 and 1.05:1.
• Four wheel drive low is stuck "off" for 3 seconds. Gear
ratio between 2.66 and 2.76:1 in any two gears.
FUSE 6B
5 AMP
INTERIOR
D
TCC/
CRUISE
C
40
C29-B9
TCC / CRUISE
BRAKE SWITCH
9-S12-069.1
®