GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2000 🢒 GMC C Pickup - 2WD 🢒 Body and Accessories 🢒 Cellular Communication 🢒 OnStar No or Poor Cellular Reception

Test Description

The following numbers refer to the steps in the table.

  1. This step inspects that the phone is presently capable of placing a call.

    2.

  2. This step inspects that the phone is presently capable of placing a call.

    3.

  3. The vehicle needs to be in a area capable of transmitting and receiving cellular communications.

    4.

  4. This step inspects the antenna for proper installation and condition.

Step

Action

Value(s)

Yes

No

DEFINITON: This procedure is for improving reception performance. The vehicle must be in a area capable of transmitting and receiving cellular signals.

1

Did you perform the OnStar® Diagnostic System Check?

--

Go to Step 2

Go to OnStar System Check OnStar® Diagnostic System Check

2

  1. Turn ON the ignition, with the engine OFF.
  2. Activate the OnStar® Center button.

Is the connection made to the OnStar® Call Center?

--

Go to Step 3

Go to Step 9

3

  1. Turn ON the ignition, with the engine OFF.
  2. Activate the Emergency button.

Is the connection made to the OnStar® Call Center?

--

Go to Step 4

Go to Step 9

4

Was the connection to the OnStar® Call Center Clear?

--

Go to Step 15

Go to Step 5

5

  1. Move the vehicle to a new area away from all buildings, high tension wires, and radio towers.
  2. Turn ON the ignition, with the engine OFF.
  3. Activate the OnStar® Center button.

Is the connection made to the OnStar® Center clear?

--

Go to Step 15

Go to Step 6

6

Check the following items:

  1. Coax the connections tight at the coupling box and the VCU.
  2. Antenna not mounted over Defogger Grid Lines.
  3. No visible damage to the antenna coupling box.
  4. Antenna not mounted over after market window tint.
  5. Antenna pointing straight up and down.
  6. Tip of antenna above the vehicle roofline.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 7

7

Is the area known for good cellular reception?

--

Go to Step 8

Go to Step 5

8

Replace the Cellular Antenna. Refer to Antenna Assembly Replacement .

Did you complete the replacement?

--

Go to Step 15

--

9

Test the XCVR RCV Data circuit for a short to battery positive or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the problem?

--

Go to Step 15

Go to Step 10

10

Test the XCVR CMP Data circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the problem?

--

Go to Step 15

Go to Step 11

11

Test the XCVR THRU Data circuit . Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the problem?

--

Go to Step 15

Go to Step 12

12

Test the XCVR DIG Return circuit for a short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the problem?

--

Go to Step 15

Go to Step 13

13

Check the following items:

  1. Coax the connections tight at the coupling box and the VCU.
  2. Antenna not mounted over Defogger Grid Lines.
  3. No visible damage to the antenna coupling box.
  4. Antenna not mounted over after market window tint.
  5. Antenna pointing straight up and down.
  6. Tip of antenna above the vehicle roofline.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

14

Replace the VIU. Refer to Vehicle Interface Unit and Vehicle Communication Unit Modules Replacement in Cellular Communications.

--

Go to Step 15

--

15

Operate the system in order to verify the repair.

Did you correct the condition?

--

System OK

Go to Step 2