For 1990-2009 cars

#### Test Description

The following procedure tests for poor performance or an inoperative hands-free microphone. The following numbers refer to the steps in the table.

1. This step verifies that the OnStar® call is successfully connected. The call may take up to 3 minutes to complete. The operator may say that this call is a "voice call with no data". This does not mean that the microphone is operating properly.

2. This step tests the microphone circuits from the microphone to the vehicle interface unit (VIU).

3. This step tests the microphone circuit between the VIU and the vehicle communication unit) VCU.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the OnStar® Diagnostic System Check? | -- | Go to Step 2 | Go to OnStar System Check
2 |

1. Turn ON the ignition, with the engine OFF.
2. Activate the OnStar® call button.
3. When you hear the OnStar® Call Center operator, speak clearly into the OnStar® microphone.

Can the OnStar® operator hear you clearly?

--

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3 |

1. Disconnect the OnStar® microphone.
2. Turn the ignition to ON with the engine OFF.
3. Measure voltage at the OnStar® microphone from the cellular telephone microphone signal circuit to the drain wire circuit.

Is voltage near the specified value?

9 volts

Go to Step 6

Go to Step 4

4 | Test the cellular telephone microphone signal circuit for a short or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 5
5 | Test the drain wire circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
6 | Test the XCVR MIC In circuit for a short B+, short to ground or an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7
7 | Inspect for poor connections at the harness connector of the OnStar® microphone. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8
8 | Replace the OnStar® microphone. Refer to Mobile Telephone Microphone Replacement in Cellular Communications. Did you complete the replacement? | -- | Go to Step 11 | --
9 | Inspect for poor connections at the harness connector of the VIU. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
10 | Replace the VIU. Refer to OnStar Vehicle Interface Unit Replacement in Cellular Communications. Did you complete the replacement? | -- | Go to Step 11 | --
11 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | --