For 1990-2009 cars

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: OnStar Schematics DEFINITION: The OnStar® call center operator can clearly be heard but the operator is unable to hear the caller.
1 | Did you perform the Cellular Communication Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Cellular Communication
2 |

1. Turn ON the ignition, with the engine OFF.
2. Press the OnStar® Call Center button.
3. Ask the OnStar® operator if your voice can clearly be heard.

Does the OnStar® operator hear your voice?

--

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

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the cellular microphone connector.
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage from the Cellular Microphone Signal circuit to a good ground.

Does the voltage measure greater than the specified value?

7 V

Go to Step 4

Go to Step 5

4 | Measure the voltage from the Cellular Microphone Signal circuit to the Cellular Microphone Low Reference circuit. Does the voltage measure greater than the specified value? | 7 V | Go to Step 7 | Go to Step 6
5 | Test the Cellular Microphone Signal circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 8
6 | Test the Cellular Microphone Low Reference circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9
7 | Test the cellular microphone low reference for a short to ground. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10
8 |

1. Leave the microphone disconnected.
2. Disconnect the VCIM connector C2.
3. Test the cellular microphone signal circuit and cellular microphone low reference circuit for a short together.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

9 | Inspect for poor connections at the harness connector of the cellular 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 13 | Go to Step 12
10 | Inspect for poor connections at the harness connector of the Vehicle Communication Interface Module. 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 13 | Go to Step 11
11 | Replace the cellular microphone. Refer to Mobile Telephone Microphone Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
12 | Important: Perform the OnStar® setup procedure. Replace the VCIM. Refer to Communication Interface Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | --
13 | Operate the system in order to verify the repair. Did you correct the condition? | -- | System OK | Go to Step 2