Hummer H1 Service Manual page 291

5-92 Transmission/Transfer Case
Stuck Off: (after two occurrences)
• Ist gear is commanded and the ratio is equal to 2nd gear
for greater than 1.7 seconds.
• 4th gear is commanded (with converter clutch locked)
and ratio is equal to 3rd gear for greater than 3 seconds.
Stuck On: (after five occurrences)
• 2nd gear is commanded and the ratio is equal to 1st gear
for greater than 2.5 seconds.
• Condition is met with 5 occurrences.
Action Taken When The DTC Sets
• The PCM will command maximum line pressure.
• The PCM will freeze shift adapts.
• The PCM will turn on the warning lamp.
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 DTC default actions when the
fault no longer exists and ignition is cycled "off" long
enough to power down the PCM.
Step
1 1. Connect scan tool.
2. Turn ignition switch on.
3. Record DTC "Freeze Frame" and Failure Records."
4. Start engine, apply brake pedal and shift to follow-
ing ranges D1, D2, D3, D4, N, R, and P.
Does each transmission range match the "TR Switch"
on the scan tool?
2 1. Raise vehicle on hoist that allows wheels to rotate.
2. Start engine, shift into D4 range, use scan tool to
command 1st, 2nd, 3rd, and 4th gears increasing
speed.
Did 2-3 or 1-4 only shift pattern occur? (Road testing
may be necessary).
3 Check the shift solenoid/hydraulic circuit for:
• Shift solenoids for an internal malfunction.
• Damaged seals on the shift solenoids.
Was a problem found and corrected?
4 1. After the repair is complete, use scan tool to select
"DTC" then "Clear Info" function.
2. Select "Specific DTC" and enter DTC "P0751."
3. Operate the vehicle under the following conditions
• Hold the throttle at 20% and accelerate to 55 mph
(if the throttle moves more than 3%, stop the ve-
hicle and start over).
• PCM must see the proper ratio for each com-
manded gear for greater than one second in D1,
D2, D3, and D4.
_____________________________________________
DTC P0751 1-2 Shift Solenoid Valve Performance
Action
Diagnostic Aids
• Verify that the transmission meets the specifications in
the 4L80-E shift speed chart.
• Other internal transmission failures may cause more
than one shift to occur.
• If any engine DTCs or TPS codes are present diagnose
and clear these DTCs first.
Test Description
The numbers below refer to the diagnostic chart.
1.This test checks pressure switch function of the PSA.
2.This test checks that the scan tool commanded all shifts,
all shift solenoids responded correctly, but all the shifts
did not occur.
4L80-E CHART
Gear
1 ON
2 OFF
3 OFF
4 ON
Value
—
—
—
—
1-2 Shift 2-3 Shift
Solenoid Solenoid
OFF
OFF
ON
ON
Yes No
Go to Pressure
Switch Assem-
bly (PSA)
Resistance
Go to Step 2 Check
Go to Diagnos-
Go to Step 3 tic Aids
—
Go to Step 4
Repair verified,
exist DTC
— table.
®