Data Link Connector Diagnosis. GMC Truck GMC C-Series Medium Duty Truck B7 1998

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 6.5L (L65) 🢒 Data Link Connector Diagnosis

Refer to Engine Controls Schematics

Cell 22: Power and Grounding, MIL and Serial Data Circuits

Engine Controls Components
Cell 22: Power
Handling ESD Sensitive Parts Notice
.

Circuit Description

There should always be a steady Malfunction Indicator Lamp (MIL) when the ignition is ON and engine OFF. Battery ignition voltage is supplied to the lamp. The PCM will turn the lamp ON by grounding the ignition feed circuit.

Test Description

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

This step verifies if the problem in the scan tool or the vehicle.

If the resistance reading is below 10 ohms, this indicates that the serial data circuit or a controller module that shares the circuit is shorted to ground or shorted internally.

By disconnecting each controller module that shares the serial data circuit and re-checking the resistance can determine if the shared controller module internally.

This step checks to determine if the serial data circuit is shorted to voltage.

A resistance reading under 10 ohms indicates that the circuit has continuity. A high resistance reading indicates an open in the circuit.

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Disconnect the scan tool from the vehicle.
Connect the scan tool to a vehicle with the same model year and with the same systems.
Turn the ignition ON leaving the engine OFF.

Does the PCM communicate with the scan tool?

Go to Step 3

Go to Step 4

Reconnect the scan tool to the original vehicle.
Turn the ignition ON leaving the engine OFF.

Does the scan tool communicate with the PCM?

Go to Step 11

Go to Step 5

The scan tool may be malfunctioning. Refer to the scan tool instruction manual.

Is the action complete?

Go to Step 17

Turn the ignition OFF.
Disconnect the PCM connectors.
With a J 39200 DMM , measure the resistance at the DLC connector between terminal 4 and terminal 2.

Is the resistance less than the specified value?

10 Ohms

Go to Step 6

Go to Step 7

Disconnect the Electronic Brake Control Module (EBCM).
Measure the resistance at the DLC connector between terminal 4 and terminal 2.
Repeat the procedure for the following shared Modules on the serial data circuit.

•	Power Steering Control Module

•	EVO Module

•	Automatic Transfer Case (ATC) Module (if equipped)

Does disconnecting one of the modules cause the resistance to be greater than the specified value?

10 Ohms

Go to Step 15

Go to Step 14

Turn the ignition ON leaving the engine OFF.
With the J 39200 DMM, measure the voltage at the DLC connector between terminal 4 and terminal 2.

Is the voltage less than the specified value?

1.0 V

Go to Step 8

Go to Step 12

Turn the ignition OFF.
With the DMM, measure the resistance between the DLC connector terminal 2 and the serial data circuit terminal at the PCM connector.

Is the resistance less than the specified value?

10 Ohms

Go to Step 9

Go to Step 13