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Hummer H1 (2006+). Manual - part 99

OBD-240

On-Board Diagnostics

_____________________________________________

Remove the transmission oil pan.

Disconnect the pressure switch manifold (PSM) from the
internal wiring harness.

Using a DVOM, measure the PSM resistance at terminals C
and B.

Is resistance within the specified value?

3,490

ohms

[commat]

20°C

(68°F)

177.9

ohms

[commat]

100°C

(212°F)

Go to Step 9

Go to Step 10

Repair the engine wiring harness.

Did you complete the repair?

Go to Step 12

Replace the AT internal wiring harness.

Did you complete the replacement?

Go to Step 12

Replace the PSM.

Did you complete the replacement?

Go to Step 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 12

Perform the following procedure in order to verify the repair:

Clear the DTC.

Using the scan tool, monitor the TFT.

Drive the vehicle under normal operating conditions. Watch
for significant changes in TFT.

Select Specific DTC.

Enter DTC P0711.

Has the test run and passed?

System OK

Go to Step 1

Step

Action

Value(s)

Yes

_____________________________________________

On-Board Diagnostics OBD-241

5745804

DTC P0712 Transmission Fluid Temperature Sensor Circuit Low Input (Figure OBD-67)

Figure OBD-67: Transmission Fluid Temperature Sensor Circuit

Circuit Description

The transmission fluid temperature (TFT) sensor is a part of the pressure switch manifold (PSM) assembly, and is located in the
transmission oil pan. The TFT sensor is a thermistor, which changes value based on the temperature of the transmission fluid. The
sensor has a negative-temperature coefficient. This means that as the temperature increases, the resistance decreases, as the temper-
ature decreases the resistance increases. The transmission control module (TCM) supplies a 5 volt reference voltage signal to the
TFT sensor and measures the voltage drop in the circuit. When the transmission is cold, the sensor resistance is high and the TCM
detects high signal voltage. As the fluid temperature warms to a normal operating temperature, the resistance becomes less and the
signal voltage decreases. The TCM uses this information to control shift quality and torque converter clutch (TCC) apply.

DTC P0712 is a type B DTC.

Conditions for Setting the DTC

DTC P0712 sets when the TCM detects a temperature greater than 150°C (302°F) for 2.5 seconds.

OBD-242

On-Board Diagnostics

_____________________________________________

Action Taken When the DTC Sets

• The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for

Setting the DTC are met.

• The TCM uses a TFT default value.

• The TCM freezes shift adapts.

• The TCM stores this information as Failure Records.

• The TCM stores DTC P0218 in TCM history.

• The TCM inhibits 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.

• A short to ground on circuit 1227 will allow a code P0712 to set.

Step

Action

Value(s)

Yes

NOTE: Before clearing DTC(s) use the scan tool “Capture info”
to record Freeze Frame and Failure Records for reference, as data
will be lost when “Clear Info” function is used

Was the “On-Board Diagnostic (OBD) System Check” per-
formed?

Go to step 2.

Go to OBD Sys-

tem Check.

Measure the transmission fluid level. Refer to Transmission Fluid
Checking Procedure.

Is the transmission fluid level correct?

Go to Step 3

Go to Transmis-

sion Fluid

Checking Proce-

dure

_____________________________________________

On-Board Diagnostics OBD-243

5745804

Install the scan tool.

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.

Record the DTC Freeze Frame and Failure Records.

Clear the DTC.

Select TFT on the scan tool.

Drive the vehicle and inspect for an unrealistic TFT reading.

Is the TFT reading at or below the specified value?

-36°C (-

32°F)

Go to Step 4

Go to Diagnos-

tic Aids

Turn the ignition OFF.

Disconnect C79 at the TCM.

Install the J 39700 breakout box and the J 43799 breakout
box adapter at C79.

Turn ON the ignition, with the engine OFF.

Using a DVOM, measure voltage at C79 terminal 10 and ter-
minal 20.

Is voltage within the specified value?

5 Volts

Go to Step 5

Go to Step 11

Turn the ignition OFF.

Using a DVOM, measure the resistance at C79 terminal 10
and terminal 20.

Is the resistance within the specified value?

3,490

ohms

[commat]

20°C

(68°F)

177.9

ohms

[commat]

100°C

(212°F)

Go to Diagnos-

tic Aids

Go to Step 6

Turn the ignition OFF.

Disconnect the transmission 20-way C34.

Using a DVOM, measure resistance at the transmission side
20-way connector terminals G and H.

Is the resistance within the specified value?

3,490

ohms

[commat]

20°C

(68°F)

177.9

ohms

[commat]

100°C

(212°F)

Go to Step 8

Go to Step 7

Step

Action

Value(s)

Yes

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