Well on the gauge and the DIC im reading 13.6-13.8 on cold start but about 12.0-12.6 when its warm. HOWEVER, on both cold start and running temp my voltage at the terminals and the alternator is 13.7 (at battery) and 13.9 ( at alternator) ... why are my DIC and gauges telling me LIES!!!!?? thanks in advance

 

The source voltage and your voltage in the car will never agree. The voltage drops through various loads and connections throughout the car. That gives you an indication of what the voltage drop is in your car and how important good connections are.

 

If you think it is way off, below is from the manual:

Voltmeter Displaying High or Low
Voltmeter is Inaccurate Step
Action
Value(s)
Yes
No

DEFINITION: The voltmeter is indicating abnormal voltage readings. The Instrument Panel Cluster (IPC) monitors Ignition 1 voltage at the IPC connector terminal A13. If the voltage reading at the IPC terminal A13 falls out of the normal range, the IPC should inform the driver by illuminating across the Driver's Information Center either the LOW VOLTAGE or HIGH VOLTAGE warning message. If PCM fault codes P0562 or P0563 exist, diagnose those first before proceeding with this table. Always ensure that a good battery is installed in the vehicle, charging system operation depends heavily on the battery condition.

1
Were you sent here from the Charging System Check?
--
Go to Step 2
Go to Charging System Check

2
Load test the battery.

Does the battery pass the load test?
--
Go to Step 5
Go to Step 3

3
Recharge the battery.
After charging, load test the battery again.
Does the battery pass the load test?
--
Go to Step 5
Go to Step 4

4
Replace the battery.

Is the repair complete?
--
Go to Charging System Check
--

5
Start the engine and allow it to idle in Park.
Load the electrical system by turning on the headlights and the high blower.
Connect a DMM between the battery terminals.
Measure the available voltage at the battery with the engine running and the electrical system under load.
Is the voltage within the specified values?
10.0-14.0V
Go to Step 6
Go to Step 11

6
Turn the ignition switch to the OFF position.
Disconnect the instrument panel cluster connector.
Connect one DMM between the battery terminals.
Connect another DMM between ground and the instrument panel cluster terminal A13.
Start the engine and allow it to idle in Park.
Load the electrical system by turning on the headlights and the high blower.
Compare the voltage readings at the instrument panel cluster terminal A13 to the voltage reading at the battery.
Are the voltage readings within 0.1 to 1.5 volts of each other?
--
Go to Step 7
Go to Step 8

7
Replace the instrument panel cluster (IPC).

Is the repair complete?
--
Go to Charging System Check
--

8
Check the IPC MiniFuse #19 fuse for an open circuit.

Is this fuse open?
--
Go to Step 9
Go to Step 10

9
Repair a short to ground in CKT 139 between the IPC and the instrument panel electrical center.

Is the repair complete?
--
Go to Charging System Check
--

10
Repair the open or high resistance in CKT 139 between the IPC and the instrument panel electrical center.

Is the repair complete?
--
Go to Charging System Check
--

11
Connect a DMM between the BATTERY terminal (CKT 2-large red wire) in the back of the generator and ground.
Measure the available voltage at the BATTERY terminal (CKT 2-large red wire) in the back of the generator.
Is the voltage within the specified values?
10.0-14.0V
Go to Step 15
Go to Step 12

12
Check the fusible link located down at the starter motor between the medium gauge blue wire (CKT 2) and the heavy gauge red wire (CKT 2). See wiring schematic for further detail.

Is the fusible link open?
--
Go to Step 13
Go to Step 14

13
Repair a short to ground in CKT 2 (13 red wire) between the generator BATTERY terminal and the fusible link.

Is the repair complete?
--
Go to Charging System Check
--

14
Repair an open in CKT 1 (19 red wire), CKT 2 (3 blue wire) or CKT 2 (13 red wire) between the generator BATTERY terminal and the positive battery terminal. See wiring schematic for further detail.

Is the repair complete?
--
Go to Charging System Check
--

15
Disconnect the generator connector.
Connect a DMM between the generator connector terminal D (CKT 2-medium red wire) and ground.
Measure the available voltage at the generator connector terminal D (CKT 2-medium red wire).
Is the voltage within the specified values?
10.0-14.0V
Go to Step 19
Go to Step 16

16
Check the fusible link located down at the starter motor between the small gauge grey wire (CKT 2) and the medium gauge red wire (CKT 2). See wiring schematic for further detail.

Is the fusible link open?
--
Go to Step 17
Go to Step 18

17
Repair a short to ground in CKT 2 (1 red wire) between the generator connector terminal D and the fusible link.

Is the repair complete?
--
Go to Charging System Check
--

18
Repair an open in CKT 1 (19 red wire), CKT 2 (0.5 grey wire) or CKT 2 (1 red wire) between the generator connector terminal D and the positive battery terminal. See wiring schematic for further detail.

Is the repair complete?
--
Go to Charging System Check
--

19
Disconnect the powertrain control module connector C2.
Connect a DMM between the generator connector terminal C (CKT 23) and the powertrain control module connector C2 terminal 11.
Measure CKT 23 for continuity between these two connectors.
Is CKT 23 continuous between the generator connector and the powertrain control module connector C2?
--
Go to Step 20
Go to Step 22

20
Powertrain control module connector C2 and generator connector are still disconnected.
Connect the DMM between the generator connector terminal C (CKT 23) and ground.
Measure CKT 23 for continuity to ground.
Is CKT 23 shorted to ground?
--
Go to Step 23
Go to Step 21

21
Powertrain control module connector C2 and generator connector are still disconnected.
DMM still connected between the generator connector terminal C (CKT 23) and ground.
Turn the ignition switch to the ON position.
Measure CKT 23 for available voltage.
Is CKT 23 shorted to battery power?
--
Go to Step 24
Go to Step 25

22
Repair the open in CKT 23 between the generator connector and the powertrain control module connector C2.

Is the repair complete?
--
Go to Charging System Check
--

23
Repair the short to ground in CKT 23 between the generator connector and the powertrain control module connector C2.

Is the repair complete?
--
Go to Charging System Check
--

24
Repair the short to battery power in CKT 23 between the generator connector and the powertrain control module connector C2.

Is the repair complete?
--
Go to Charging System Check
--

25
Connect a DMM between the generator connector terminal B (CKT 225) and the powertrain control module connector C2 terminal 77.
Measure CKT 225 for continuity between these two connectors.
Is CKT 225 continuous between the generator connector and the powertrain control module connector C2?
--
Go to Step 26
Go to Step 28

26
Powertrain control module connector C2 and generator connector are still disconnected.
Connect the DMM between the generator connector terminal B (CKT 225) and ground.
Measure CKT 225 for continuity to ground.
Is CKT 225 shorted to ground?
--
Go to Step 29
Go to Step 27

27
Powertrain control module connector C2 and generator connector are still disconnected.
DMM still connected between the generator connector terminal B (CKT 225) and ground.
Turn the ignition switch to the ON position.
Measure CKT 225 for available voltage.
Is CKT 225 shorted to battery power?
--
Go to Step 30
Go to Step 31

28
Repair the open in CKT 225 between the generator connector and the powertrain control module connector C2.

Is the repair complete?
--
Go to Charging System Check
--

29
Repair the short to ground in CKT 225 between the generator connector and the powertrain control module connector C2.

Is the repair complete?
--
Go to Charging System Check
--

30
Repair the short to battery power in CKT 225 between the generator connector and the powertrain control module connector C2.

Is the repair complete?
--
Go to Charging System Check
--

31
Replace the generator.

Is the repair complete?
--
Go to Charging System Check
--

 

I have the same problem. Seems to be you need to get some one with a tech2 that can adjust the signal from the PCM to the gauges.

I got this from a GM Tech.