POOR FM PERFORMANCE W/CDM (RETURN AC DELCO SERV. CTR.)

SUBJECT: POOR FM RADIO PERFORMANCE WITH CDM RECEIVER BOXES (RETURN TO AC DELCO SERVICE CENTRE)

VEHICLES AFFECTED: ALL 1992 MODELS EXCEPT "M,R,S,T" CARS AND "J1,E1,G" TRUCKS

APPLICATIONS: 1992 Model Year ------------- Chevrolet: B, F, J, L, W, Y Carlines C/K, M/L, S/T, U Trucks Pontiac: F, H, J, N, W Carlines, U Truck Oldsmobile: B, C, E, H, N, W Carlines, U and T Trucks Buick: A, B, C, E, H, N, W Carlines Cadillac: C, D, E, K, V Carlines GMC: C/K, M/L, S/T Trucks

CONDITION:

---------- Some 1992 vehicles equipped with a CDM (Communication Data Module) receiver box may exhibit one or more of the following conditions on FM stations: both channels fade, right channel fades, loss of volume, radio switching from stereo to mono, or treble cutting out.

CORRECTION:

----------- For 1992 vehicles with any of the symptoms listed above, verify that the receiver box is both a CDM and a 1992 model radio.

There are two ways that CDM receivers are mounted: a remote mounted receiver box, and a receiver box integral with the radio control head.

1. Remote Mounted Receiver Box - this type of radio has the box mounted in a different location from the control head. All these receiver boxes are CDM.

Remove the receiver box to locate the bar code serial number label, shown in Figure 2. A large "2" means that the unit is a 1992 model. If the serial number begins with a "3", or "4", the receiver box should be sent in for service to an authorized AC DELCO service centre. If the serial number begins with "5", the latest changes have been made internally, and other causes for the conditions should be investigated.

2. Integral Receiver Radio - Remove the radio to determine if it is a CDM unit. This type of radio is a two piece unit with the receiver box bolted to the control head to form one unit, as shown in Figure 1.

Locate the bar code serial number label, shown in Figure 2. A large "2" means that the unit is a 1992 model. If it is a 1992 unit, return the integral receiver radio to an authorized AC DELCO service centre.

For vehicles repaired under, warranty use:

Use labour operation R0750, with appropriate time.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.