For 1990-2009 cars

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

#### SUBJECT: FM RECEPTION CONDITIONS (EXCHANGE CDM RADIO RECEIVER)

#### MODELS AFFECTED: 1992 DE VILLES, FLEETWOODS (WITH CD PLAYERS, ONLY), ELDORADOS, SEVILLES, BROUGHAMS, AND ALLANTES (CDM RADIOS AS LISTED ON PAGE 13 OF DSIB 92-I-1)

Some 1992 DeVille, Fleetwood (with CD player only), Eldorado, Seville, Brougham, or Allante owners may complain of erratic FM reception. The complaint may be described as:

"One channel goes dead for a few seconds." "Sounds like the volume decreases." "Some instruments drop out." "Right door speaker infermittently fades."

This may be caused by the radio receiver changing from FM stereo to mono in an attempt to improve the listening quality of the station when it senses FM multi-path interference. Multi-path interference is caused when the vehicle passes near large objects that can reflect the FM signal, although it may happen at other times.

To diagnose the condition, drive the vehicle outdoors near buildings or other large structures with the radio tuned to a moderately strong FM station and listen for a condition that might be described as above. The Multi-path Interference Reduction (MIR) condition may last for a few seconds or longer and the "ST" (stereo) annunciator light will not go off.

The Tech 1 scan tool may be used to simulate the radio changing from stereo to mono (not applicable to DeVilles and Fleetwoods). With the vehicle outdoors, tune in an AM stereo station. AM stereo may be turned "ON" and "OFF" with the Tech 1 and the effect compared with the symptom in question. Refer to the 1992 Eldorado and Seville Service Information Manual, pages 9A-6, 7 for instructions.

On Eldorados, Sevilles, Broughams, and Allantes remove the remote receiver to locate the bar code serial number label sbown in Figure 1. A large "2" in the lower right corner means that the unit is a 1992 model. If the serial number begins with a "3" or "4", the remote receiver should be sent in for service to an authorized AC-Delco Service Center. If the serial number begins with "5" or a large "3" is present, the latest changes have been made internally and other causes for the condition should be investigated.

On DeVilles and Fleetwoods with Bose CD remove the radio to determine if it has an affected CDM receiver. This type of radio is a two-piece unit with the receiver bolted to the control head to form one unit. Separate the receiver by removing three screws to gain access to the label and follow the procedure above to examine the serial number. Refer to Figure 2.

To repair the condition pre-exchange the radio (DeVilles and Fleetwoods) or remote radio receiver (Eldorados, Sevilles, Broughams, and Allantes) at an authorized AC-Delco repair center as described in DSIB 92-I-1.

If the AC-Delco shop does not have the part number you need in stock, contact the AC-Delco locator service at (313) 635 -1542 between the hours of 7:30 AM and 4:30 PM Eastern Daylight Time.

For warranty purposes use Labor Operation R0750 at the times shown below:

WARRANTY INFORMATION VEHICLE SERIES -------------------- Operation -------------- Operation Description Number C D E K V --------------------- --------- ---- ---- ---- ---- ---- Receiver, Radio - R&R R0750 .2 .7 .3 .3 .3 Diagnosis Time O-.3 O-.3 O-.3 O-.3 O-.3

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.