O/D Main Switch & O/D Off Indicator Light Circuit

O/D MAIN SWITCH & "O/D OFF" INDICATOR LIGHT CIRCUIT

CIRCUIT DESCRIPTION
The O/D Main Switch contacts are OFF when the switch is in the IN position, and ON when the switch is in the OUT position. In the IN position, the "O/D OFF" indicator lights up, and the engine control module (ECM) prohibits shifting to overdrive.
The ECM also causes the "0/D OFF" indicator light to blink when a malfunction is detected. However, when the O/D Main Switch is IN, the "0/D OFF" indicator light will not blink, but stays ON. In this case, connecting the terminals in the DLC1 can not display the trouble code.

WIRING DIAGRAM

O/D Main Switch and O/D Off Indicator Light Circuit:

INSPECTION PROCEDURE
1. Check O/D main switch function.




a. Turn ignition switch ON.
b. Push the O/D main switch out (OFF) and check "O/D OFF" indicator lamp.
OK: "O/D OFF" indicator lamp comes ON.
c. Push the O/D main switch in (ON) and check "O/D OFF" indicator lamp.
OK if: "O/D OFF" indicator lamp goes OFF.

NOTE:
If the "O/D OFF" indicator lamp blinks when the main switch is ON, a malfunction is occuring in the system. Check for trouble codes as described in Procedures / How To Display And Read diagnostic trouble codes.
^ OK: Proceed to step 2.
^ NG: Go to step 4.
2. Check voltage between terminal "OD2" of the engine control module (ECM) and body ground.




a. Turn ignition switch ON.
b. Check voltage between terminal OD2 and body ground.
OK:
O/D Main Switch OFF (out).....below 1 volt
O/D Main Switch ON (in)......10 - 14 volts
^ OK: Proceed to step 3.
^ NG: Go to next circuit inspection indicated on Matrix Chart for Electronically Controlled Circuits. (Non-Trouble Code Charts)
Matrix Chart of Problem Symptoms
3. Check harness and connectors between "O/D OFF" indicator lamp and the ECM.
^ OK: Check and replace ECM.
^ NG: Repair or replace harness or connector.
4. Check O/D main switch continuity.




a. Disconnect O/D main switch connector.
b. Measure resistance between terminals 2 and 4 of the O/D main switch connector.
OK:
O/D main switch ON (in)....No continuity.
O/D main switch OFF (out)......Continuity.
^ OK: Check and replace combination meter.
^ NG: Replace O/D main switch.