Hummer H1 Service Manual page 318

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DTC P1871 Undefined Gear Ratio
AUTOMATIC TRANSMISSION
FLUID PRESURE MANUAL VALVE POSITION SWITCH
(TFP)
D2
SWITCH
D4
SWITCH
D
P
C34
C32-S
C29-B4
TRANS
RANGE C
IINPUT
9-S12-071.1
Circuit Description
The PCM calculates ratio based on transmission input and out-
put speed sensor readings. The PCM compares known trans-
mission ratio to calculated ratio, for gear range selected.
This DTC detects an unknown ratio.
Conditions For Seating The DTC
The following conditions are met for 10 seconds.
• No DTCs P0121, P0122, P0123, P0220, P0221, P0222,
P0223, P0225, P0226, P0227, P0228.
• No DTCs P0716 or P0717.
• No DTCs P0722 or P0723.
• No DTCs P1810.
• No Four Wheel Drive Lo DTC P1875.
• Four Wheel Drive Lo fail counters are clear.
• Vehicle Speed is greater than 11 km/h (7 mph).
• Throttle angle is greater than 25%.
• Transmission fluid temperature is greater than 20°C
(68°F).
• 4.5 seconds since last gear change.
• Engine Speed is greater than 3650 rpm.
• Engine Torque is between 80 and 450 ft/ lbs.
• Gear Ratio is greater than 2.63 or less than 0.70
• Above conditions occur for 10 seconds.
05745159
LO
SWITCH
REV
D3
SWITCH
SWITCH
E C
R N
C32-H C32-K
C29-B6
C29-B5
TRANS TRANS
RANGE B RANGE A
INPUT INPUT
Transmission/Transfer Case
AUTO TRANS
INPUT SHAFT
SPEED SENSOR
A/T ISS
A
B
T W I S T E D T W I S T E D
PA I R PA I R
C32-B A
C27-D1
C27-D11
A / T ISS A / T ISS
LOW
HIGH
POWERTRAIN CONTROL MODULE (PCM)
Action Taken When The DTC Sets
• The PCM will command maximum line pressure.
• The PCM will freeze shift adapts.
Conditions For Clearing The MIL/DTC
• The PCM will turn the warning lamp off after three con-
secutive ignition cycles without a failure reported.
• The DTC can be cleared using the scan tool.
• The PCM will cancel the DTC default actions when a
fault no longer exists, and the ignition is cycled "Off"
long enough to power down the PCM.
Diagnostic Aids
• Inspect the wiring for poor electrical connection at the
PCM and the transmission 20-way connector.
• When diagnosing for a possible intermittent short or
open condition, move or wiggle the wiring harness
while observing test equipment for a change.
• If any engine DTC(s) or TP Sensor codes are present in
memory, diagnose and clear the engine DTC(s) first.
Then check to see if the transmission DTC(s) have reset.
Test Description
The numbers below refer to the diagnostic table.
1. This test checks indicated range signal to the actual
selected range. A faulty switch could set pressure
switch DTC P1870.
2. This test checks for proper ratios when in each com-
manded gear state.
5-119
TRANFER CASE
VEHICLE
SPEED
SENSOR
VSS
A
B
C33-B A
DIGITAL RATIO ADAPTER
C29-A6
C29-A3
VSS VSS