Hummer H1 Service Manual page 1068

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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.
05745159
PCM/Tech 1 Scan Tool 3
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")