GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C-Series Medium Duty Truck B7 🢒 Engine 🢒 Engine Controls - 6.5L (L65) 🢒 Malfunction Indicator Lamp (MIL) Inoperative

Refer to Engine Controls Schematics

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


Object Number: 244500 Size: FS
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.

Diagnostic Aids

If the engine cranks but will not run, check:

    • Continuous battery-fuse or fusible link for open.
    • PCM ignition fuse for open.
    • Battery Feed circuit to PCM for open.
    • Ignition Feed circuit to PCM for open.
    • Poor connection to PCM.

Test Description

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

  1. This step will isolate the problem in the MIL control circuit.

    2.

  2. If the Battery Feed, Ignition Feed and Diagnostic Test circuits have voltage, the PCM connections, grounds, or PCM are malfunctioning.

    3.

  3. Refer to PCM terminal end view in this section for PCM pin locations of ground circuits.

    4.

  4. If the fuse/fusible link is open, refer to PCM Wiring Diagram for complete circuit.

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

Attempt to start the engine.

Does the engine start?

--

Go to Step 3

Go to Step 6

3

Check the fuse number 4.

Is the fuse OK?

--

Go to Step 4

Go to Step 14

4

Turn the ignition ON. Probe the ignition feed circuit at the cluster connector with a test light to ground.

Is the test light ON?

--

Go to Step 5

Go to Step 11

5
  1. Turn the Ignition OFF.
  2. Disconnect the blue PCM connector.
  3. Turn the ignition ON.
  4. With a fused jumper wire connected to ground, probe the MIL control circuit at the PCM connector.
  5. Observe the MIL.

Is the MIL ON?

--

Go to Step 9

Go to Step 10

6

Check the PCM Ignition Feed and Battery Feed fuses.

Are both of the fuses OK?

--

Go to Step 7

Go to Step 13

7
  1. Turn the ignition OFF.
  2. Disconnect the PCM connectors.
  3. Turn the ignition ON.
  4. Probe the PCM harness ignition and battery feed circuits with a test light to ground.

Is the test light ON both circuit?

--

Go to Step 8

Go to Step 12

8
  1. Check for a malfunctioning PCM ground or a poor PCM ground connection.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 20

Go to Step 9

9
  1. Check for a poor connection at the PCM.
  2. If a poor connection is found, repair as necessary.

Was a problem found?

--

Go to Step 20

Go to Step 15

10
  1. Check the MIL control circuit for an open.
  2. If the MIL control circuit is open, repair as necessary.

Was a problem found?

--

Go to Step 20

Go to Step 16

11

Repair open in the ignition feed circuit to the cluster connector.

Is the action complete?

--

Go to Step 20

--

12

Locate and repair open in the PCM battery feed circuit or the PCM ignition feed circuit as necessary.

Is the action complete?

--

Go to Step 20

--

13

Locate and repair short to ground in the PCM Ignition Feed circuit or the PCM Battery Feed circuit as necessary.

Is the action complete?

--

Go to Step 20

--

14

Locate and repair short to ground in the instrument cluster Ignition Feed circuit.

Is the action complete?

--

Go to Step 20

--

15

Replace the PCM.

Important: If the PCM is faulty, The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 20

--

16
  1. Check the MIL control circuit for a poor connection at the instrument cluster connector.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 20

Go to Step 17

17
  1. Remove the instrument cluster.
  2. Inspect the MIL bulb.

Is the bulb OK?

--

Go to Step 19

Go to Step 18

18

Replace the MIL bulb.

Is the action complete?

--

Go to Step 20

--

19

Replace the instrument cluster.

Is the action complete?

--

Go to Step 20

--

20
  1. Using the Scan Tool, select DTC, Clear Info.
  2. Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 21

Go to Step 2

21
  1. Allow engine to idle until normal operating temperature is reached.
  2. Select DTC, Failed This Ign.

Are any DTCs displayed?

--

Go to the Applicable DTC Table

Go to Step 22

22

Using the Scan Tool, select Capture Info, Review Info.

Are any DTCs displayed that have not been diagnosed?

--

Go to the Applicable DTC Table.

System OK