Radio - Buzzing Noise in AM Band With Engine Running

Group Ref.: Accessories

Bulletin No.: 449601

Date: April, 1994

SUBJECT:
BUZZING NOISE IN AM BAND OF RADIO (INSTALL FILTER ON PCM/TCM)

MODELS:
1992-94 CHEVROLET AND GMC TRUCK C/K, S/T TRUCKS AND M/L, G VANS
1992-94 OLDSMOBILE BRAVADA WITH 4L60-E AND 4L80-E TRANSMISSIONS

CONDITION:

Some owners may comment of a buzzing noise in the low end of the AM radio band with the engine running.

CAUSE:

The switching of the force motor in the electronic transmission emits an RFI signal through the PCM/TCM. The AM band of the radio is receiving this interference through the antenna.

CORRECTION;

To determine if this is the cause of the owner's comments. first duplicate the condition and then disconnect the electrical connector at the transmission (this will disable the force motor). If the condition improves. install an in-line filter (P/N 1224205) to the ignition lead (ckt 439) of the PCM/TCM. Some applications may have two (439 ckt), in which case, a filter will be required for each lead.

NOTE:
Disconnecting the electrical connector at the transmission will set the transmission diagnostic codes. It will be necessary to remove these codes after the corrective action has been performed.

IMPORTANT:
Discard the instructions in the filter package. This filter Is an in-line filter with a single lead on one end and two leads on the other end (one lead being black (ground). Install this filter as close to the PCM/TCM connector as possible. It Is important to Install the filter with the single lead end going toward the PCM/TCM and then take the black (ground) lead back and attach it to the case of the PCM/TCM. If this filter is installed incorrectly, the condition will become worse.


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