Hummer H1 (2002+). Manual - part 70

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 Transmission/Transfer Case  5-79

®

05745159

 DTC P0724 Brake Switch Circuit High Input

Step

Action

Value

Yes

No

1

1.

Install scan tool. 

2.

Turn ignition switch “on.”

NOTE: Important:

 Before clearing DTC(s), use the

scan tool to record “Failure Records” for reference, as
data will be lost when the “Clear Info” function is used. 

3.

Record the DTC “Failure Records.”

4.

Select “Brake Switch” on the scan tool.

5.

Disconnect the brake switch connector from he 
brake switch.

Did the brake switch status change from “Closed” to 
“Open?”

—

Go to Step 2

Go to Step 3

2

Replace brake switch. 

—

Go to Step 5

—

3

Check switch wires circuit for short to B+.
Was a problem found?

—

Go to Step 5

Go to Step 4

4

Replace the PCM.
Is the replacement complete?

—

Go to Step 5

—

5

1.

After the repair is complete, use the scan tool to 
select DTC,” then “Clear Info” function.

2.

Select “Specific DTC” and enter DTC “P0724.”

3.

Ensure the following conditions are met:

• Select “Brake Switch” on scan tool, depress 

brake pedal. Switch state should change as pedal 
is depressed.

—

—

—

5-80

Transmission/Transfer Case

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®

DTC P0730 Incorrect Gear Ratio

Circuit Description

The Powertrain Control Module (PCM) calculates a ratio based
on the Automatic Transmission Input Shaft Speed Sensor (A/T
ISS) and Vehicle Speed Sensor (VSS) readings. The PCM
compares the known transmission gear ratio to the calculated
ratio, for the selected gear range.

If the PCM detects an incorrect gear ratio, then DTC P0730
sets. DTC P0730 is a type D DTC.

Conditions for Setting the DTC

The following conditions are met for 7 seconds:

• No MAP DTCs P0106, P0107, P0108.

• No A/T ISS Sensor DTCs P0716 or P0717.

• No OSS Sensor DTCs P0722 or P0723.

• No TFP Valve Position Switch DTC P1810.

• The Vehicle Speed is greater than 11 km/h (7 mph).

• The APP Angle is greater than 25%.

• The TFT is greater then 20ºC (68ºF).

• System voltage is 9.0-16.0 volts.

• Ten seconds must have elasped since the last gear range 

change.

• The engine speed is greater than 475 RPM for at least 7 

seconds.

• The engine speed is less than 3750 RPM.

• The engine torque is 100-642 N•m (80-475 lb ft).

• The Gear Ratio is one of the following:

• -Greater than 2.52 or less than 2.42

-Greater than 2.12 or less than 2.04
-Greater than 1.50 or less than 1.45
-Greater than 1.02 or less than 0.98
-Greater than 0.77 or less than 0.73
-Greater than 2.52 or less than 2.42

Action Taken When the DTC Sets

• The PCM does not illuminate the Malfunction Indicator 

Lamp (MIL).

• The PCM commands maximum line pressure.

• The PCM freezes shift adapts.

• DTC P0730 is stored in PCM memory.

Conditions for Clearing the DTC

• A scan tool can clear the DTC from the PCM history. 

The PCM clears the DTC from the PCM history if the 
vehicle completes 40 warm-up cycles without a failure 
reported.

• The PCM cancels the DTC default actions when the 

fault no longer exits and the ignition is OFF long 
enough to power down the PCM.

Diagnostic Aids

• Sticking or contaminated shift valves may cause an un-

defined gear ratio.

• Refer to the Shift Solenoid Valve State and Gear Ratio 

table.

• First diagnose and clear any engine DTCs that are 

present. Then inspect for any transmission DTCs that 
may have reset. If a DTC P0717 Input Speed Sensor 
Circuit Low Input

 and a DTC P0730 are both present, 

diagnose DTC P0717 first.

• DTC P1870 detects an incorrect gear ratio in fourth gear 

with TCC applied.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

3. This step tests the indicated range signal to the actual

selected range. A faulty TFP Valve Position Switch
could set DTC P0730.

4. This step tests for proper ratios in each commanded

gear state.

Range

Gear

1-2 Sol

2-3 Sol 

Fourth

Clutch

Overrun

Clutch

O/D 

Roller

Clutch

FWD

Clutch

Direct

Clutch

Front

Band

Interm.

Sprag 

Clutch

Interm

Clutch

Lo

Roller

Clutch

Rear

Band

Overdrive

1st

On

Off

– – H

A

–

–

*

–

H

–

2nd

Off

Off

– – H

A

–

–

H

A

O

–

3rd

Off

On

– – H

A

A

–

O

A

O

–

4th

Off

On

A

– O

A

A

–

O

A

O

–

A=Applied
H=Holding
*=Holding but not effective
O=Overrunning

____________________________________________

 Transmission/Transfer Case  5-81

®

05745159

 DTC P0730 Incorrect Gear Ratio 

Step

Action

Value

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) Sys-
tem Check performed?

–

Go to Step 2

Go to Power-

train OBD 

System Check

2

Perform the Transmission Fluid Checking Procedure.
Refer to Transmission Fluid Checking Procedure.
Is the Procedure complete?

–

Go to Step 3

Go to Trans-

mission Fluid 

Checking Pro-

cedure

3

1.

Install the scan tool.

2.

With the engine OFF, turn the ignition switch to 
the RUN position.
Important:

 Before clearing the DTCs, use the 

scan tool in order to record the Failure Records for 
reference. Using the Clear Info function erases the
stored Failure Records from the PCM.

3.

Record the DTC Freeze Frame and Failure 
Records, then clear the DTCs.

4.

Start the engine.

5.

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? (Refer to the Range Signal 
table).

–

Go to Step 4

Refer to DTC 

P1810 TFP 

Valve Postion 

Switch CKT 

Malfunction

 in 

this section

4

1.

Drive the vehicle in Reverse and D4.

2.

Hold the vehicle speed above 11 km/h (7mph) for 
greater than 2 seconds in the specified gear range.

3.

Use the scan tool snapshot mode in order to record 
the transmission gear ratio for each commanded 
gear range: Reverse, 1st, 2nd, 3rd and 4th.

Are the gear ratios within the parameters for each spec-
ified gear range?

Rev–2.04-2.12
1st–2.52-2.42
2nd–1.45-1.50
3rd–0.98-1.02
4th–0.73-0.77

Refer to Diag-

nostic Aids

Go to Step 5

5

1.

Connect the J–21867 Pressure Gauge to the trans-
mission line pressure tap.

2.

Perform the Line Pressure Checking Procedure.
Refer to Line Pressure Check Procedure.

Is the line pressure within specifications for each 
selected gear range?

–

Go to Step 6

Go to Step 8

6

1.

Remove the transmission oil pan.
Refer to Changing the Fluid and Filter, in On-Vehi-
cle Service.

2.

Inspect the oil pan and the fluid for contamination.

Did you find excessive contamination?

–

Go to 

Transmission 

Overhaul 

Procedure, in 

Unit Repair

Go to Step 7

7

Inspect the transmission for the following problems:

• Sticking shift valves

• Stuck apply pistions

Did you find the condition?

–

Go to Step 10

Go to

Transmission

Overhaul

Procedure, in

Unit Repair.

5-82

Transmission/Transfer Case

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®

8

Is the system line pressure low only in the specific gear 
which indicated an incorrect gear ratio?

–

Go to Step 9

Go to System

Diagnosis 

Table; Low

Line Pressure

9

Inspect for fluid pressure loss in the following areas:

• 1-2 SS Valve seal

• 2-3 SS Valve seal

• Valve body passages

• Valve body gaskets

• Band apply pistons and seals

• Clutch apply pistons and seals

Did you find the condition?

–

Go to Step 10

Go to

Transmission

Overhaul

Procedure,

in Unit Repair

10

In order to verify your repair, perform the following 
procedure:
1.

Select DTC.

2.

Select Clear Info.

3.

Operate the vehicle under the following condi-
tions:

• Start the engine

• Drive the vehicle in Reverse, 1st, 2nd, 3rd and 

4th gear

• The PCM must see a valid gear ratio versus the 

commanded gear ratio for 7 seconds

4.

Select Specific DTC. Enter DTC P0730.

Has the test run and passed?

–

System OK

Begin the 

diagnosis 

again.

Go to Step 1

 DTC P0730 Incorrect Gear Ratio (Cont’d)

Step

Action

Value

Yes

No