GM Service Manual Online
For 1990-2009 cars only

Circuit Description

Modules connected to the Class II serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes. Diagnostic trouble codes (DTCs) may be set due to this symptom and during this diagnostic procedure. Complete the diagnostic procedure in order to ensure all the DTCs are diagnosed and cleared from memory.

Diagnostic Aids

    • When the Class II serial data circuit is shorted to ground, U1300 or U1305 will be set. Refer to DTC U1300 Class 2 Data Link Low or DTC U1305 Class 2 Data Link Low or High in Data Link Communications.
    • When the Class II serial data circuit is shorted to battery positive voltage U1301 or U1305 will be set. Refer to DTC U1301 Class 2 Data Link High or DTC U1305 Class 2 Data Link Low or High in Data Link Communications.

DLC Diagnosis

Step

Action

Values

Yes

No

1

Did you perform the Powertrain On Board Diagnostic (OBD) System Check?

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Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn ON the ignition, with the engine OFF.
  2. Attempt to communicate with the PCM.

Does the scan tool communicate with the PCM?

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Go to Diagnostic Aids

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications