GM Service Manual Online
For 1990-2009 cars only

Refer to

Instrument Cluster, IP, and the DLC


Object Number: 20435  Size: FS
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Engine Controls Components
Vehicle Control Module VCM
CMP, CKP, ICM, and the Ignition Coil
OBD II Symbol Description Notice
.

Circuit Description

There should always be a steady MIL when the ignition is ON and the engine is stopped. The battery supplies voltage to the lamp. The VCM turns ON the lamp by grounding the MIL control circuit whenever a DTC sets and the DTC meets the requirements for illuminating the MIL.

Test Description

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

  1. This step checks the battery feed circuit to the DLC.

  2. This step checks the DLC grounds.

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

With a test light connected to ground, probe the DLC connector battery feed circuit (Pin 16).

Is the test light ON?

--

Go to Step 3

Go to Step 11

3

With a test light connected to B+, probe the DLC connector (Pins 4 and 5).

Is the test light on for both circuits?

--

Go to Step 4

Go to Step 12

4

Check for proper operation of the cigarette lighter.

Does the cigarette lighter operate properly?

--

Go to Step 5

Go to Step 13

5

Verify the proper operation of the scan tool with a known good vehicle with the same equipment and controller.

Does the scan tool communicate with a known good vehicle

--

Go to Step 6

Go to Step 14

6

  1. Connect a DVM to ground.
  2. Check the voltage on the serial data line at the DLC connector (Pin 2).

Is the voltage on the serial data line less than the specified value?

7.0 V

Go to Step 7

Go to Step 16

7

With the DVM connected to ground, check the serial data line at the DLC connector (Pin 2).

Is the voltage less than the specified value?

1.0 V

Go to Step 8

System OK

8

  1. Turn the ignition OFF.
  2. With the DVM connected to a ground, check the resistance of the serial data line at the DLC connector (Pin 2).

Is the resistance less than the specified value?

10 ohms

Go to Step 9

Go to Step 10

9

  1. Disconnect the VCM connectors.
  2. With the DVM connected to a ground, check the resistance of the serial data line (Pin 2).

Is the resistance less than the specified value?

10 ohms

Go to Step 17

Go to Step 15

10

Repair the open in the serial data circuit.

Is the action complete?

--

Go to Step 18

--

11

Repair the open in the battery feed circuit to the DLC connector (Pin 16). Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 18

--

12

  1. Repair the open circuit that did not light the test light. Refer to Wiring Repairs in Engine Electrical.
  2. Refer to Engine Electrical for ground distribution.

Is the action complete?

--

Go to Step 18

--

13

Repair the cigarette lighter.

Is the action complete?

--

Go to Step 18

--

14

  1. Repair a faulty can tool if necessary.
  2. Replace a faulty can tool if necessary.
  3. Repair a faulty cable if necessary.
  4. Replace a faulty cable if necessary.

Is the action complete?

--

Go to Step 18

--

15

Repair short to ground in the serial data line. Refer to Wiring Repairs in Engine Electrical.

Is the action complete

--

Go to Step 18

--

16

Repair the short to voltage in the serial data line. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 18

--

17

Replace the VCM.

Important: the new VCM must be programmed. Refer to VCM Replacement/Programming

Is the action complete?

--

Go to Step 18

--

18

  1. Using the scan tool, select the DTC and the Clear Info.
  2. Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 19

Go to Step 2

19

  1. Allow the engine to idle until the engine reaches normal operating temperature.
  2. Select the DTC and the Failed Ign.

Are any DTCs displayed?

--

Go to The Applicable DTC Table

Go to Step 20

20

Using the scan tool, select the Capture Info and the Review Info.

Are any DTC displayed that have not been diagnosed.

--

Go to The Applicable DTC Table

System OK