Hummer H1 (2002+). Manual — part 267

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PCM/Tech 1 Scan Tool 1

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05745159

General Information

The control module system has a computer, Powertrain Con-
trol Module (PCM) to control fuel delivery timing, and some
emission control systems.

The control module system, monitors a number of engine and
vehicle functions and controls the following operations:

• Fuel control

• Fuel injection timing

• Speed Control

• Turbocharger Boost

• Transmission shift and shift quality functions. Specific

transmission control diagnostics are covered in Section
5 of this service manual.

Powertrain Control Module (PCM)

The diesel Powertrain Control Module (PCM) is located in the
passenger compartment and is the control center of the control
module system.

The PCM constantly looks at the information from various sen-
sors, and controls the systems that affect vehicle performance.
The PCM performs the diagnostic function of the system. It
can recognize operational problems, alert the driver through
the MIL (Check Engine), and store one or more DTCs which
identify the problem areas to aid the technician in making re-
pairs.

The PCM is designed to process the various input information
and then send the necessary electrical responses to control fuel
delivery, timing and other emission control systems. The input
information has an interrelation to more than one output, there-
fore, if the one input failed it could effect more than one sys-
tem’s operation.

PCM Function

The PCM supplies a buffered 5 or 12 volts to power various
sensors or switches. This is done through resistances in the
PCM which are so high in value that a test light will not light
when connected to the circuit. In some cases, even an ordinary
shop voltmeter will not give an accurate reading because its re-
sistance is too low. Therefore, the use of a 10 megaohm imped-
ance digital voltmeter is necessary to assure accurate voltage
readings.

Reprogramming (“Flashing”) The Control
Module

Some vehicles allow reprogramming of the control module
without removal from the vehicle. This provides a flexible and
a cost-effective method of making changes in software and cal-
ibrations.

Verifying Vehicle Repair

Verification of vehicle repair will be more comprehensive for
vehicles with OBD II system diagnostics. Following a repair,
the technician should perform the following steps:

1. Review and record the fail records and/or Freeze Frame data

for the DTC which has been diagnosed (Freeze Frame data
will only be stored for an A or B type diagnostic and only
if the MIL has been illuminated).

2. Clear DTC(s).

3. Operate the vehicle within conditions noted in the fail

records and/or Freeze Frame data.

4. Monitor the DTC status information for the specific DTC

which has been diagnosed until the diagnostic test associ-
ated with that DTC runs.

Following these steps is very important in verifying repairs on
OBD II systems. Failure to follow these steps could result in
unnecessary repairs.

Reading DTCs Using A Scan Tool

The recommended method for reading DTC(s) stored in mem-
ory is by using diagnostic Scan Tool plugged into the DLC.
Follow instructions supplied by tool manufacturer.

“On-Board Diagnostic (OBD) System
Check”

After the visual/physical under hood inspection, the
“On-Board Diagnostic (OBD) “System Check” is the starting
point for all diagnostic procedures and for locating the cause of
an emissions test failure.

The correct procedure to diagnose a fault is to follow three ba-
sic steps.

1. Are the on-board diagnostics working? This is determined

by performing the “On-Board Diagnostic (OBD) System
Check.” If the on-board diagnostics are not working, refer
to diagnostic charts in this section. If the on-board diag-
nostics are working properly, the next step will be:

2. Is there a DTC stored? If a DTC is stored, go directly to the

numbered DTC chart in this section. This will determine if
the fault is still present. If no DTC is stored, the next step
will be:

3. Scan Tool serial data transmitted by the control module.

This involves displaying the information available on the se-
rial data stream with a Scan Tool or one of the tools avail-
able for that purpose. Information on these tools and the
meaning of the various displays can be found in this section.
Normal readings under a particular operating condition can
be found below the chart “On-Board Diagnostic (OBD) Sys-
tem Check.”

2

PCM/Tech 1 Scan Tool

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Diagnostic Information

The diagnostic table and functional checks in this manual are
designed to locate a faulty circuit or component through logic
based on the process of elimination.

The charts are prepared with the requirements that the vehicle
functioned correctly at the time of assembly and that there are
no multiple failures.

The PCM performs a continual self-diagnosis on certain con-
trol functions. This diagnostic capability is complemented by
the diagnostic procedures contained in this manual. The
PCM’s language for communicating the source of a malfunc-
tions is a system of DTCs.

Malfunction Indicator Lamp (MIL) “Check
Engine”

This light is on the instrument panel and has the following
functions.

• It informs the driver that a problem has occurred and

that the vehicle should be taken in for service as soon as
reasonably possible.

• It displays DTCs stored by the PCM which help the

technician diagnose system problems.

As a bulb and system check, the light will come “ON” with the
key “ON” and the engine not running. When the engine is
started, the light will turn “OFF.” If the light remains “ON,”
the self-diagnostic system has detected a problem. If the prob-
lem goes away, the light will go out in most cases after 10 sec-
onds, but a DTC will remain stored in the PCM.

When the light remains “ON” while the engine is running, or
when a malfunction is suspected due to a driveability or emis-
sions problem, an “On-Board Diagnostic (OBD) System
Check” must be performed. This check will expose malfunc-
tions which may not be detected if other diagnostics are per-
formed prematurely.

“Check Throttle” Lamp

This light is on the instrument panel and has the following
functions:

• It informs the driver that a problem has occurred in the

Accelerator Pedal Position (APP) circuit and the vehicle
should be taken in for service as soon as reasonably pos-
sible.

• If APP DTCs are stored by the PCM, the MIL will dis-

play these. The “Check Throttle” Lamp will not display
DTCs.

As a bulb and system check, the light will come “ON” with the
key “ON” for 2 seconds. When the engine is started, the light
will turn “OFF.” If the light remains “ON,” the self-diagnostic
system has detected a problem. If the problem goes away, the
light will go out in most cases after 10 seconds, but a DTC will
remain stored in the PCM.

When the light remains “ON” while the engine is running, or
when a malfunction is suspected, an “On-Board Diagnostic

(OBD) System Check” must be performed. This check will ex-
pose malfunctions which may not be detected if other diagnos-
tics are performed prematurely.

Circuit Description

The “On-Board diagnostic (OBD) System Check” is an orga-
nized approach to identifying a problem created by a control
module system malfunction. It must be the starting point for
any driveability complaint diagnosis, this will direct the ser-
vice technician to the next logical step in diagnosing the com-
plaint. Understanding the chart and using it properly will
reduce diagnostic time and prevent the unnecessary replace-
ment of good parts.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic
Table.

1. When the ignition switch is cycled to “ON,” the MIL should

turn “ON” and remain “ON” steady. This sequence will
determine that the vehicle diagnostics are operational.

2. Use Scan Tool to aid diagnosis, therefore, serial data must

be available.

3. Although the PCM is powered up, a “Cranks But Will Not

Run” symptom could exist because of a PCM or system
problem.

4. Comparison of actual control system data with the Typical

Scan Tool Data Values is a quick check to determine if any
parameter is not within limits. A base engine problem (i.e.,
advanced cam timing) may substantially alter sensor values.

5. This step will isolate if the customer complaint is a MIL or

driveability problem with no MIL. Refer to “DTC Identifi-
cation” in this Section for a list of valid DTCs. An invalid
DTC may be the result of a faulty Scan Tool, PROM or
PCM.

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PCM/Tech 1 Scan Tool 3

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05745159

Tech 1 Scan Tool

The diagnostic procedures in this manual assume the use of a
Tech 1 scan tool. Since the Tech 1, produced by Expertec, is
able to perform functions, such as, bidirectional communica-
tion that other scan tools are unable to perform, it has been
made an essential tool. Although, the term scan tool will con-
tinue to be used for simplicity’s sake, we recommend the Tech
1 be used whenever possible. Explicit instructions on connect-
ing and using the various Tech 1 functions are contained in the
Tech 1 owner’s manual.

The PCM can communicate a variety of information through
Data Link Connector (DLC) terminal “M.” This data is trans-
mitted at high frequency which requires a scan tool for inter-
pretation.

Powertrain Control Module (PCM)

Service of the PCM should normally consist of replacement of
the PCM.

If the diagnostic procedures call for the PCM to be replaced, it
will be necessary to program the EEPROM in the PCM using
the procedure in this section

Important

• When replacing the production PCM with a service

PCM, a DTC P1214 will be stored. It is important to
program “TDC Offset” into the service PCM. Refer to
“PCM Programming (TDC Offset).”

Important

• When a PCM has been replaced, a short glow plug dura-

tion will exist during the first ignition cycle (less than 2
seconds). After the first ignition cycle, the glow plug
system will operate properly.

Important

• When replacing the production PCM with a service

PCM (controller), it is important to transfer the broad-
cast code and production PCM number to the service
PCM label. Please Do Not record on PCM cover. This
will allow positive identification of PCM parts through-
out the service life of the vehicle.

Important

• To prevent internal PCM damage, the ignition must be

“OFF” when disconnecting or reconnecting power to
PCM (for example, battery cable, PCM pigtail, PCM
fuse, jumper cables, etc.). The ignition should be “OFF”
for at least 30 seconds before disconnecting power to
the PCM.

PCM Replacement

Remove or Disconnect

1. Negative battery cables.

2. PCM from passenger compartment.

3. Connectors from PCM.

4. PCM mounting hardware.

CAUTION:

To prevent possible electrostatic discharge to

the PCM, do not touch the component leads, and do not
remove integrated circuit from carrier.

Install or Connect

1. PCM mounting hardware.

2. Connectors to PCM.

3. PCM in passenger compartment.

4. Negative battery cables.

NOTE:

The MIL, antilock and brake lamps will continue

to be enabled until the PCM is programmed. Once the
programming is complete, the lamps will be turned
“OFF” and normal operation will occur.

5. Proceed to “PCM Programming (EEPROM)”

PCM Programming (EEPROM)

1. Set up:

• Battery is charged.

• Ignition is “ON.”

• Battery/Cig. Lighter connection secure.

• Data Link Connector attached.

2. Refer to up-to-date Techline terminal/equipment user’s in-

structions.

3. If PCM fails to reprogram, do the following:

• Check all PCM connections.

• Check Techline terminal/equipment for latest software

version.

• Try again to reprogram PCM. If it fails again, replace

the PCM. Refer to PCM replacement.

4. Allow vehicle to idle until coolant temperature is greater

than 170°F (77°C) (refer to “PCM Programming TDC Off-
set”)

4

PCM/Tech 1 Scan Tool

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POWERTRAIN OBD SYSTEM CHECK

Circuit Description

The On Board Diagnostic System Check is an organized ap-
proach to identifying a problem created by an electronic engine
system fault. The OBD system check is the starting point for
any driveability diagnosis. The OBD system check directs the
service technician to the next step in diagnosing the complaint.
Do not perform this check if no driveability complaint exists.
Understanding the table correctly reduces the diagnostic time.
Understanding the table correctly prevents the replacement of
good parts.

Diagnostic Aids

Important: Do not clear the DTCs unless directed by a diagnos-
tic procedure. Clearing the DTCs will also clear valuable
freeze frame and failure records data.

Inspect all related wiring and connections including the con-
nections at the PCM. These may cause and intermittent mal-
function.

Check any circuitry that is suspected of causing an intermittent
problem for the following conditions:

• Backed out terminals

• Improper mating

• broken locks

• Improperly formed or damaged terminals

• Poor terminal to wiring connections

• Physical damage to the wiring harness

• Corrosion

• Poor pin tension

Test Description

The numbers below refer to the step number in the diagnostic
table.

1. When the ignition is turned on, the MIL will momentarily

flash ON and OFF and then remain on until the engine is
running if no Diagnostic Trouble Codes are stored.

2. The diagnostic tables in this section are designed for use

with a properly functioning scan tool. Before beginning any
other diagnostic procedures, correct the serial data commu-
nications. The Class II serial data will not transmit if the sys-
tem voltage measures below 9v or above 16v.

3. Whenever multiple DTCs are stored, refer to the DTC tables

in the following order:

a.

PCM Error DTCs

b.

System voltage DTCs

c.

Component level DTCs (DTCs that indicate a faulty
part

d.

System level DTCs (DTCs that indicate a system
fault).

5. By storing the Freeze Frame Data and the Failure records se-

lection in the scan tool, an electronic copy of the freeze
frame data and the failure records taken when the fault oc-
curred is stored, which can be referred to later.

6. Checking the sensors for proper operation during warm up

can be a crucial step in correctly diagnosing any driveability
concern. Careful observation of these sensors during the en-
gine warm up may reveal a slow responding sensor or a sen-
sor that malfunctions only within a small portion of its
range.

After the engine is at the normal operating temperature, a com-
parison of the actual control system data with the typical values
is a quick way to determine if any parameter is not within lim-
its. Keep in mind that a base engine problem may substantially
alter sensor values.

Check the following sensors for proper operation:

• The Engine Coolant Temperature Sensor (ECT) for ini-

tial coolant temperature reading at ambient. Then ob-
serve the rise in the temperature while the engine is
warming up.

• The Intake Air Temperature Sensor (IAT) for initial air

temperature reading at ambient. Then observe the rise in
the temperature while the engine is warming up.