GM Service Manual Online
For 1990-2009 cars only
Table 1: Radio Features
Table 2: Cassette Features
Table 3: Compact Disc Features

Radio Features

Controls

Radio UM7

Radio UM6

Radio U1C

Power

Push PWR/VOL knob to turn the radio on.

Volume

The volume is adjusted by rotating the PWR/VOL knob.

Tune

Turn the RCL/TUNE knob.

Seek

Momentarily press the SEEK button.

Scan

Hold SEEK for 4 seconds.

Presets

Six AM, Six FM1, AND Six FM2

Preset Saving

Press and hold desired button until an audible beep is heard.

Recall

Push the RCL/TUNE button.

Fade or Balance

Press the AUDIO button to select, then use arrow keys to change.

Bass or Treble

Press the AUDIO button to select, then use the arrow keys to change.

Cassette Features

Controls

Radio UM7

Radio UM6

Radio U1C

Eject

--

Eject Button

--

Fast Forward

Preset Button 4

Reverse

Preset Button 3

Auto Reverse

Yes

Side

Preset Button 5

Previous

Preset Button 1

Next

Preset Button 2

Scan

Hold Seek for 5 seconds

Repeat

Preset Button 6

Compact Disc Features

Controls

Radio UM7

Radio UM6

Radio U1C

Eject

--

--

Eject Button

Fast Forward

Preset Button 4

Reverse

Preset Button 3

Previous

Preset Button 1

Next

Preset Button 2

Scan

Hold Seek for 5 seconds

Repeat

Preset Button 6

Random

Preset Button 5

Each item in the list below represents topics covered in detail below:

    • AM/FM Reception
    • Antenna
    • Theft Deterrent
    • Radio Error Messages

AM/FM Reception

Radio Signal

The radio signal is sent from a broadcast station and then is received by the antenna. The strength of the signal depends on the following:

    • The power output - wattage - of the broadcast station
    • The location of the vehicle - or receiver- relative to the broadcast tower
    • Obstacles between the tower and the receiver
    • Atmospheric conditions
    • What band - AM or FM - the station is broadcasting
    • Type of antenna and the ground plane

AM Reception

The AM band has a lower frequency range than the FM band. These longer wavelengths:

    • Bend around obstacles
    • Follow the curve of the Earth
    • May reflect off the ionosphere

The AM frequencies have a longer range due to the ground wave. The ground wave follows the curvature of the Earth and is affected by its conductivity. Greater conductivity equates to less signal loss, thus transmission over water is better than over land. The AM band has a range of 80-320 km (50-200 mi).

FM Reception

The shorter wavelengths of the higher frequency FM band:

    • Reflect off obstacles
    • Are absorbed by the ground
    • Penetrate the ionosphere

Broadcasts in the FM band are limited to "line of sight" reception, which is typically 40 km (25 mi). Even when out of direct line of sight, the signal may be reflected into areas that would be in a "shadow" otherwise. Factors that affect the line of sight would include:

    • Height of the broadcast antenna
    • Height of the receiving antenna
    • Terrain and buildings in the broadcast path

Antenna

The antenna system is comprised of a fixed mast antenna that receives radio signals from the broadcast tower.

Theft Deterrent

The theft deterrent system is a feature of all base radios. There is no need to program a security code into the radio, as in the past model years. The theft deterrent system now utilizes class 2 serial data to determine if the radio is in the appropriate vehicle. Each time the radio receives the "run" power mode message, it compares the VIN information it has stored to the VIN information received, from a module on the class 2 serial data circuit. If a mismatch occurs, the radio display will indicate to the user that the radio is locked. Once this takes place, a DTC will set, then the radio will not respond to any button press and it will become inoperative. The only way to unlock the radio is by using a scan tool. Always refer to the table in this section to diagnose the "Theftlock" DTC for further information.

The 2 scenarios able to cause this condition are:

  1. A radio is installed from another vehicle.
  2. A module which communicates on the class 2 serial data circuit, which supplies the VIN information to the radio, is replaced and not properly setup with the VIN information for that vehicle.

Radio Error Messages

ERR:

This message is displayed when the radio is unable to play the inserted cassette or CD.

LOC:

This message is displayed when the radio has entered Theft mode.

CAL:

This message is displayed when the radio has detected an invalid calibration.