Data Link Communications System: Overview GMC Savana H2500

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Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 1. A DTC U1001 - U1254 Lost Communications with XXX with a history status may indicate the cause of U1000 or U1255.
2. 2. The modules not communicating are the likely cause of U1000 or U1255. The modules that are available on the class 2 serial data circuit are listed in the Circuit Description.
3. 6. The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001 - U1254 Lost Communications with XXX for those modules that it was monitoring.
4. 9. The modules which can communicate indicate the module which cannot communicate. You must clear the serial data communication DTCs from these modules to avoid future misdiagnosis.
5. 12. If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.
6. 14. The module which set U1000 or U1255 is the likely cause of the malfunction.

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The number below refers to the step number on the diagnostic table.

1. 6. The module which was not communicating on the class 2 serial data circuit may have set Loss of Communication DTCs for those modules that it was monitoring.

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The number below refers to the step number on the diagnostic table.

1. 4. If the battery positive voltage and ground circuits of the DLC are functioning properly. The malfunction must be due to the scan tool.

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The numbers below refer to the step numbers on the diagnostic table.

1. 2. A partial loss of communication in the class 2 serial data circuit uses a different procedure than a total loss of communication of the class 2 serial data circuit.
2. 4. The following DTCs may be retrieved with a history status. These DTCs are not the cause of the present condition. U1300 U1301 U1305
3. 6. A State of Health DTC with a history status may be present along with a U1000 or U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.
4. 10. Normal class 2 serial data communication cannot take place until the body control module (BCM) sends the appropriate power mode message. If the BCM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
5. 12. Normal class 2 serial data communication cannot take place until the body control module (BCM) sends the appropriate power mode message. If the BCM does not send a wake-up message, other modules on the class 2 serial data circuit may not communicate.
6. 17. If there are no current DTCs that begin with the letter "U", the communication concern has been repaired.
7. 18. The communication concern may have prevented diagnosis of the customer complaint.

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1. Remove the bolts/screws from the data link connector.
2. Remove the lower data link connector.

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1. Place the data link connector into position. CAUTION: Refer to «FASTENER NOTICE»(ref-175132-S17785009232005041500000) .
2. Install the bolts/screws to the data link connector. Tighten Tighten the bolts/screws to 2 N.m (18 lb in).