1987 Buick Electra BaseFACTORY OEM SERVICE PROCEDURE

Decoder Module

  1. Place ignition switch in "RUN" position. Probe decoder module terminals and measure voltage to ground. See DECODER MODULE INPUT VOLTAGES table. Place gear selector switch in positions indicated.
    DECODER MODULE INPUT VOLTAGES

    Terminal (Wire Color) Voltage Gear Position
    L (White/Black) Battery All
    J (Dark Blue) Battery All
    B (Black/White) Battery P, R, D, 2
    C (Yellow) Battery R, N, (D), D
    D (Gray) Battery (D), D, 2, 1
    E (White) Battery P, N, D, 1
  2. If voltage readings are correct, go to next step. If none of the voltage readings are correct, check White/Black wire for an open circuit. If voltage reading at any terminal is incorrect, check appropriate wire for an open circuit. If wire is okay, replace gear selector switch. See Fig 1 .
  3. Probe decoder module again and measure voltage readings to ground. See DECODER MODULE OUTPUT VOLTAGES table. If voltage reading at any terminal is incorrect, check affected circuit for shorts to ground. If no short is found, replace decoder module.
  4. If all voltage readings are correct, check Light Green/Black wire and Dark Blue wires for an open circuit. If wires are okay, perform INSTRUMENT CLUSTER C1 & C2 CONNECTOR PIN TEST  .
DECODER MODULE OUTPUT VOLTAGES

Terminal (Wire Color) Voltage Gear Position
H (Light Green) Battery R
K (Lt. Green/Black) Battery P
N (Orange/Black) (1) P, N
N (Orange/Black) Battery R, (D), D, 2, 1
G (Dk. Blue/White) (2) R, (D), D, 2, 1
(1) Reading should be less than one volt.
(2) Reading should change rapidly between 1.3-2.4 volts.
Fig 1: Decoder Module Connector
G8163Courtesy of GENERAL MOTORS CORP.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.