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Test Step 10. Check Battery Voltage to the Connector P501 for the Air Inlet Heater Relay
TM-9-2320-312-24-2 Truck Tractor Yard Type: 46 662 GVWR DED 4x2 M878A2 Manual
Illustration 36 Schematic for ATA Data Link with 6-pin connector
TM 9-2320-312-24-2
Troubleshooting Section
Repair: Repair the wiring from the connector P501
for the air inlet heater relay to the ECM connector
ATA (SAE J1587 / J1708) Data
P2. Verify that the problem has been resolved.
Link Circuit - Test
SMCS Code: 1408-081; 1901-081
No Proceed to Test Step 12.
System Operation Description:
Test Step 12. Test the Battery Voltage to
the ECM
Use this procedure under the following situation:
A. Turn the ignition key switch to the OFF position.
Use this procedure if ET will not power up or ET
will not communicate with the ECM through the cab
B. Disconnect the ECM vehicle harness connector
data link connector.
J1/P1 and install a breakout T.
The following background information is related
C. Connect a voltmeter between terminal 52 of the
to this procedure:
breakout harness and terminal 65 of the breakout
harness. Refer to Illustration 35.
The ATA data link (American Trucking Association)
is the standard data link that is used by the
D. Turn the ignition key switch to the ON position
ECM to communicate with electronic service
and check the voltmeter.
tools. The SAE specification J1587 defines the
format of the messages and data that is being
E. Turn the ignition key switch to the OFF position.
communicated. The SAE specification J1708
defines the hardware requirements and the protocol
F. Connect a voltmeter between terminal 53 of the
of the serial communications. The Caterpillar
breakout harness and terminal 67 of the breakout
Electronic Technician (ET) is an example of one
harness. Refer to Illustration 35.
of the electronic service tools. Some electronic
dashboards use this data link to receive information.
G. Turn the ignition key switch to the ON position
Some automatic transmissions also receive
and check the voltmeter.
information from this data link.
Expected Result:
The ECM provides the following two ATA data link
connection terminals from the ECM vehicle harness
The voltage is between 11.0 VDC and 13.5 VDC
connector J1:
when the ignition key switch is in the ON position.
Terminal 9 (J1587 DATA LINK NEGATIVE)
Terminal 8 (J1587 DATA LINK POSITIVE)
The vehicle OEM provides twisted pair wiring from
Repair: Replace the ECM. Verify that the problem
the ECM to the cab data link connector.
is resolved.
Remember that there are potentially several devices
that are installed in the vehicle and remember that
these devices are connected to the ATA data link
at one time. These devices include dash displays,
trip recorders and transmission controls. These
Repair: Inspect the vehicle wiring. Repair the
devices may cause problems with the data link.
vehicle wiring or send the vehicle to the OEM
These problems can disrupt communications to the
dealer for repair. Verify that the problem has been
engine ECM and from the engine ECM.
When the ignition key switch is in the OFF
position, the ECM may communicate with ET.
The communications may be disrupted and the
communications may require frequent reconnection.
In order to avoid this problem, turn the ignition key
switch to the ON position when ET is being used.
The Caterpillar Electronic Technician (ET) may
indicate the following error message:

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