Hummer H1 Service Manual page 319

5-120 Transmission/Transfer Case
Step
1 Was the powertrain On-Board Diagnostic (OBD) Sys-
tem Check Performed?
2 Perform the transmission fluid checking procedure.
Refer to Fluid Level and Condition.
Is the procedure complete?
3 1. Install the scan tool.
2. With the engine OFF, turn the ignition switch to
the RUN position.
3. Record the DTC Freeze Frame and Failure
Records.
4. Record the DTCs.
5. Start the engine.
6. Apply the parking brake, and select each transmis-
sion range: D1, D2, D3, D4, N, R, and P.
Does the scan tool TFP switch A/B/C display match
each selected gear range?
4 1. Drive the vehicle in 1st, 2nd, and 3rd gear with
greater than 25% APP.
2. Hold the vehicle speed above 7mph (11km/h) for
greater than 2 seconds in each specified gear range.
3. Use the snapshot mode in order to record the trans-
mission gear ratio for each commanded gear range:
1st, 2nd, and 3rd.
Are the gear ratios within the parameters for each spec-
ified range?
5 1. Connect the transmission pressure gauge to the
transmission line pressure tap.
2. Perform the line pressure test. Refer to the Line
Pressure Check Procedure.
Is the line pressure within specifications for each
selected gear range?
6 1. Remove the transmisson Oil pan.
2. Inspect the oil pan and the fluid for contamination.
Did you find excessive contamination?
7 Is the system line pressure low only in the specified
gear which indicated an incorrect gear ratio?
8 Inspect for fluid pressure loss in the 1-2 and 3-4 Shift
Solenoid Valve Seals
Did you find a problem?
DTC P1871 Undefined Gear Ratio
Action
NOTE: Before clearing the DTCs, use the scan
tool in order to record the Freeze Frame and
Failure Records for reference.
___________________________________________
Value
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Yes No
Go to Power-
train OBD
Go To step 2 system Check
Go to Trans-
mission Fluid
Level and
Go to step 3 Condition
Refer to DTC
P1810 Pres-
sure Switch
Assembly
Malfunction,
Go to step 4 in this section
Refer to Diag-
nostic Aids Go to Step 5
Go to Step 6 Go to Step 8
Replace the
transmission Go to Step 7
Go to Sytem
Diagnosis
Table; Low
Go to Step 8 Line Pressure
Replace the
Go to Step 10 transmission
®