No MIL light in key on/motor off

[2001CamaroGuy]

2004 Tahoe. For some reason the MIL indicator light is not turning on with key on/motor off and thus I can't get through emissions (failed yesterday when I went through). The MIL light "works" as I can trigger it with a scanner (don't know if error codes will cause it to turn on as everything is working as it should). I have even re-loaded a stock tune to ensure it wasn't a "tuning issue" without any change.

What would cause the MIL indicator light to do this? Need to know ASAP cause I need to have it done by the end of the month.

Thanks,

Chris

[mecanicman]

Malfunction Indicator Lamp (MIL) Inoperative
Circuit Description
The battery positive voltage is supplied directly to the malfunction indicator lamp (MIL). The powertrain control module (PCM) turns the MIL ON by grounding the MIL control circuit. When the ignition is ON and the engine is OFF, the MIL should be steady.

MIL Operation
The MIL is located on the instrument panel.

MIL Function
The MIL informs the driver that a malfunction has occurred. The vehicle should be serviced as soon as possible.
The MIL illuminates during a bulb test and during a system test.
A DTC will be stored if the diagnostic requests a MIL.
MIL Illumination
The MIL will illuminate with ignition switch ON, and with the engine not running.
The MIL will turn OFF when the engine is started.
The MIL will remain ON if the self-diagnostic system detects a malfunction.
The MIL may turn OFF if the malfunction is not present.
If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated if the ignition switch is ON.
If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.
Diagnostic Aids
If the problem is intermittent, refer to Intermittent Conditions .

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

This step determines if the condition is with the MIL control circuit or the PCM.

This step determines if a voltage is being applied to the control circuit.

Step
Action
Yes
No

Schematic Reference: Engine Controls Schematics

1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2
Inspect the fuse that supplies the voltage to the MIL.

Is the fuse open?
Go to Step 10
Go to Step 3

3
Turn OFF the ignition.
Disconnect the PCM. Refer to Powertrain Control Module (PCM) Replacement
Turn ON the ignition, with the engine OFF.
Connect a 3-ampere fused jumper wire between the MIL control circuit and a good ground.
Observe the MIL.
Is the MIL illuminated?
Go to Step 9
Go to Step 4

4
Did the fuse in the jumper wire open?
Go to Step 11
Go to Step 5

5
Remove the instrument panel cluster (IPC). Refer to Instrument Panel Cluster (IPC) Replacement in Instrument Panel, Gages, and Console.
Test the MIL control circuit for an open between the PCM and the IPC. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
Go to Step 14
Go to Step 6

6
Probe the MIL battery positive voltage circuit at the IPC harness connector with a test lamp connected to a good ground.

Does the test lamp illuminate?
Go to Step 8
Go to Step 7

7
Repair the open in the MIL battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
Go to Step 14
--

8
Inspect for poor connections at the harness connector of the IPC. Repair any conditions as necessary. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 14
Go to Step 12

9
Inspect for poor connections at the harness connector of the IPC and repair as necessary. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 14
Go to Step 13

10
Repair the short to ground in the MIL battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.
Replace the fuse.
Did you complete the repair?
Go to Step 14
--

11
Repair the short to voltage in battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
Go to Step 14
--

12
Replace the (IPC). Refer to Instrument Panel Cluster (IPC) Replacement in Instrument Panel, Gages, and Console.

Did you complete the replacement?
Go to Step 14
--

13
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .

Did you complete the replacement?
Go to Step 14
--

14
Operate the system in order to verify the repair.

Did you correct the condition?
System OK
Go to Step 2

[2001CamaroGuy]

Ouch.... so it looks like I need to replace the PCM? As I said I can "manually" turn the MIL on/off with a scanner through the OBD2 port so #s 1-12 are not the issue, which leaves only the PCM (#13). But if the PCM is bad, I wouldn't think I could trigger the light with a scanner?

Thanks,
Chris

[mecanicman]

If it were me, I would pull the cluster(easy to get out) and confirm the wiring. I have attached the schematic. Make sure there power to the MIL with key off/on as it always supposed to be hot. Then check to see if pcm grounds the light with koeo. Make sure you use a led test light or high impedance test box or they will not work when you are done.

Open your glove box and look at rpo codes, see if there is an 8s8 on the list. You will need to know to follow the wiring in the diagram.