Hummer H1 (2006+). Manual — part 120
OBD-324
On-Board Diagnostics
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Action Taken When the DTC Sets
• The TCM illuminates the malfunction indicator lamp (MIL).
• When in a forward range, the transmission will fail to another forward range, unless the transmission is compromised by
over speeding or direction change, then the transmission will shift to NEUTRAL while diagnostic response is active.
•
If the shift selector is moved from a forward range to NEUTRAL or from a forward range to REVERSE, the transmission
will shift to NEUTRAL.
• If the shift selector is moved to REVERSE, the transmission will shift to REVERSE if it is not compromised by over
speeding or a direction change. If compromised, the transmission will shift to NEUTRAL.
• DTC P0840 will be stored in TCM history.
• The TCM freezes shift adapts.
• The TCM inhibits torque converter clutch (TCC) engagement.
Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle com-
pletes 40 warm-up cycles without failure.
Diagnostic Aids
• Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
• A bent terminal
• A backed-out terminal
• A damaged terminal
• Poor terminal tension
• A chafed wire
• A broken wire inside the insulation
• When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a
change.
• You may have to drive the vehicle in order to experience a condition.
• This DTC may indicate that C solenoid is mechanically defective or the shift valve is stuck in the stroked state.
• When a P0840 and P0842 are set in combination, this may indicate a short to ground at the pressure switch circuit or the
shift valve is stuck in the stroked state.
Step
Action
Value(s)
Yes
No
1
Did you perform the Diagnostic System Check - Vehicle?
Go to Step 2
Go to
Diagnostic
System Check
2
Measure the transmission fluid level. Refer to Transmission Fluid
Checking Procedure.
Is the transmission fluid level correct?
Go to Step 3
Go to
Transmission
Fluid Checking
Procedure
3
Measure the line pressure.
Is the pressure within the specified value?
Go to Step 4
Go to
Symptoms
Automatic
Transmission
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On-Board Diagnostics OBD-325
5745804
4
1.
Install the scan tool.
2.
Turn ON the ignition, with the engine OFF.
NOTE: Before clearing the DTC, use the scan tool in order to
record the Freeze Frame and Failure Records for reference. The
Clear Info function will erase the data.
3.
Record the DTC Freeze Frame and Failure Records.
4.
Clear the DTC.
5.
Start the engine.
6.
Using the scan tool, monitor TFP SW. C status.
Does the scan tool indicate TFP SW. C status is ON?
Go to
Diagnostic Aids
Go to Step 5
5
1.
Turn the ignition OFF.
2.
Disconnect C79 at the TCM.
3.
Install the J 39700 breakout box and the J 43799 breakout
box adapter at C79.
4.
Connect terminal 1 to a known good ground.
5.
Turn ON the ignition, with the engine OFF.
Does the scan tool indicate TFP SW. C status is ON when
grounded and OFF when open?
Go to Step 6
Go to Step 12
6
1.
Turn the ignition OFF.
2.
Connect the C79 to the TCM.
3.
Disconnect the transmission 20-way connector C34.
4.
Turn the ignition ON. Additional DTCs might be set.
5.
Connect C34 terminal D to a known good ground.
Does the scan tool indicate TFP SW. C status is ON when
grounded and OFF when open?
Go to Step 7
Go to Step 11
7
1.
Remove the oil pan. Refer to Transmission Oil Pan Replace-
ment.
2.
Disconnect the AT internal wiring harness from the PSM and
ground terminal A.
Does the scan tool indicate TFP SW. C status is ON when
grounded and OFF when open?
Go to Step 8
Go to Step 10
8
1.
Remove the PSM from the control valve body and leave the
internal harness connected.
2.
Provide a ground connection for the PSM to either the con-
trol valve body or the transmission main case.
3.
Using the eraser end of a pencil, push gently on the pressure
switch C membrane.
Does the scan tool indicate TFP SW. C status is ON when
grounded and OFF when open?
Go to
Diagnostic Aids
Go to Step 9
9
Replace the faulty PSM.
Did you complete the replacement?
Go to Step 13
10
Replace the AT internal wiring harness.
Did you complete the replacement?
Go to Step 13
11
Repair engine wiring harness circuit for an open or short.
Did you complete the repair?
Go to Step 13
Step
Action
Value(s)
Yes
No
OBD-326
On-Board Diagnostics
_____________________________________________
12
NOTE: In most cases, the TCM is not at fault. Investigate thor-
oughly before replacing the TCM.
Replace the faulty TCM.
Did you complete the replacement?
Go to Step 13
13
Perform the following procedure in order to verify the repair:
1.
Clear the DTC.
2.
Start the engine.
3.
Using the scan tool, monitor TFP Sw. C status.
4.
Select Specific DTC.
5.
Enter DTC P0840.
Has the test run and passed?
System OK
Go to Step 1
Step
Action
Value(s)
Yes
No
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On-Board Diagnostics OBD-327
5745804
DTC P0841 Transmission Pressure Switch Solenoid C Stuck Off (Figure OBD-85)
Figure OBD-85: Transmission Pressure Switch Solenoid C Circuit
Circuit Description
The pressure switch manifold (PSM) is a multiple-switch assembly made up of three normally open (N/O) and one normally closed
(N/C) pressure switches. The C pressure switch monitors C shift valve positioning and relays it to the transmission control module
(TCM). When C pressure switch is in the open state, C shift valve should be in the unstroked position.
DTC P0841 is a type A DTC.
Conditions for Setting the DTC
DTC P0841 sets when C solenoid is commanded ON and pressure switch C status remains OFF for 5 seconds depending on fluid
temperature.
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