Decoder Module

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

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 .
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.
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

K (Lt. Green/Black)

Battery

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

Courtesy of GENERAL MOTORS CORP.