Hummer H1 Service Manual page 205

5-6 Transmission/Transfer Case
AUTOMATIC TRANSMISSION INPUT (SHAFT)
SPEED SENSOR AND OUTPUT (SHAFT) SPEED
SENSOR (VEHICLE SPEED SENSOR)
The input and vehicle speed sensors are variable reluctance,
magnetic pickup units (Figure 5-7). They consist of a perma-
nent magnet surrounded by a wire coil. The sensors are
mounted in the driver side of the transmission case and the top
of the transfer case at the rear.
The vehicle speed sensor is positioned opposite the speedome-
ter tone wheel in the rear of the transfer case. The input sensor
is opposite the machined teeth on the forward clutch housing in
the transmission (Figure 5-7). The tone wheel and gear teeth
interrupt the sensor magnetic field as they rotate. This induces
an AC current in each sensor coil. The vehicle sensor provides
a voltage signal proportional to vehicle speed. The input sensor
signal indicates transmission shaft/turbine speed. Both sensor
signals are used by the PCM to determine shift speed, pattern,
and converter clutch apply.
Sensor signals reaching the PCM are converted to a square
wave form (Figure 5-7). The wave forms correspond to the
teeth on the speedometer tone wheel and forward clutch. The
increase in shaft speed will cause more teeth to interrupt the
sensor magnetic field in a given time. This is reflected in an in-
crease in the number of wave forms sent to the PCM. The wave
forms are compared to a fixed signal voltage in the PCM to de-
termine speeds.
O-RING
MAGNETIC PICKUP
(MAGNET AND COIL)
FOWARD CLUTCH
GEAR TEETH OR
SPEEDOMETER
TONE WHEEL
LOW SPEED
5.0
CONDITIONED SQUARE WAVE SIGNAL
Figure 5-7: Transmission Speed Sensor Signal Form
______________________________________________
ELECTRICAL
CONNECTOR
SPEED
SENSOR
HIGH SPEED
TIME
TRANSMISSION FLUID TEMPERATURE SENSOR
The fluid temperature sensor is mounted on the internal trans-
mission harness. Failure of the sensor constitutes wiring har-
ness replacement. It is a temperature sensitive resistor more
commonly known as a thermister (Figure 5-8). Low fluid tem-
perature produces high resistance. The PCM controls torque
converter clutch apply based on sensor input signals.
The PCM will not allow converter clutch apply when fluid
temperature is below 68°F (20°C). At higher fluid tempera-
tures, the PCM will apply or release the converter clutch as fol-
lows:
• Apply the clutch in second, third, fourth when fluid tem-
perature exceeds 250°F (122°C).
• Release the clutch and prevent apply in any gear range
when fluid temperature reaches or exceeds 300°F
(150°C).
• Prevent converter clutch apply and set a-fault code
when fluid temperature reaches 310°F (154°C).
SENSOR
ELEMENT
16,000
133
-10°C
+16°F
Figure 5-8: Temperature Sensor
®
TEMPERATURE
SENSOR
110°C
230°F