For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using the diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptors

DTC U2201 00: Lost Communication With Entertainment Head Unit (EHU)

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Mid Speed GMLAN Serial Data Circuits | 1 | 1 | 1 | --
B+ | U2201, 2 | U2201, 2 | -- | --
Ground | -- | U2201, 2 | -- | --
1. Scan tool does not communicate with mid speed GMLAN device 2. Radio Inoperative

### Circuit/System Description

Modules connected to the mid speed GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.

### Conditions for Running the DTC

• | The system voltage is between 9-16 volts.

• | The vehicle power mode requires serial data communication to occur.

### Conditions for Setting the DTC

A supervised periodic message that includes the transmitter module availability has not been received.

### Action Taken When the DTC Sets

The module uses a default value for the missing parameters.

### Conditions for Clearing the DTC

• | A current DTC clears when the malfunction is no longer present.

• | A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction.

### Diagnostic Aids

• | Use Data Link References to determine if the module uses mid speed GMLAN serial data communications

• | Some modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no module output voltage circuit is shorted to ground before replacing the module.

• | An open fuse located on the radio near the power connector would cause the radio to not communicate with other modules.

### Reference Information

• | Data Communication Schematics

• | Control Module References

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool References

Control Module References for scan tool information

### Circuit/System Testing

Note: Use the schematic to identify the following:

• | Control modules the vehicle is equipped with

• | Control module locations on the mid speed GMLAN serial data circuit

• | The control modules B+, ignition, ground, communication enable and serial data circuit terminals

1. Ignition OFF, disconnect the harness connector of the radio.
2. Test for less than 5 Ω between each ground circuit terminal and ground.

⇒ | If greater than the specified range, test the ground circuit for an open/high resistance.

3. Verify that a test lamp illuminates between each B+ circuit terminal and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits for a short to ground. If the circuits test normal, replace the radio.

4. If equipped, ignition ON, verify that a test lamp illuminates between each ignition circuit terminal and ground.

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the control circuits for a short to ground. If the circuits test normal, replace the radio.

5. Ignition OFF for 60 seconds, test for less than 5 Ω between the radio connector terminals and DLC terminals listed below:

• | Radio connector terminal 9 and DLC terminal 3

• | Radio connector terminal 10 and DLC terminal 11

⇒ | If greater than the specified range, test the serial data circuit for an open/high resistance between the radio and a module setting the DTC.

6. If all circuits test normal, replace the radio.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | GMLAN Wiring Repairs

• | Control Module References for module replacement, setup, and programming