There is no "overdrive light". The yellow Arrow light indicates that the Overdrive (4th gear) is disengaged. Normally you'd never see that "Upshift Arrow" Unless you'd pushed the button on the shifter lever.

This is because the OD relay is automatically turned on when you start the car. When the OD relay is on, the Arrow light will be off and voltage from the OD relay will be "relayed" to the OD solenoid on the tranny. If you decide to downshift while driving, the shifter button will turn the OD relay OFF (arrow ON) then on again when you want to go back into Overdrive.

Anytime you see the Up Arrow, it means the OD relay is OFF. If you didn't turn the relay off with the shifter button, it could be something like a blown fuse or a failing OD relay. Maybe the following circuit outline will help you understand the OD operation:

OD operation involves 4 components and the wiring that connects them...

1) Fuse 11 (200) or 12 (700/900) supplies voltage to items #2, #3, and #4.

2) The Shifter button/switch turns the OD relay off and on [Button is flush with the back surface of the shifter knob on '93 940]

3) The OD relay controls the OD solenoid and the Upshift ("OD off") Arrow light (by separate wires). When the Arrow light is ON, the OD relay and solenoid are OFF.

4) The OD solenoid allows OD engagement when ON, (this is the "default" OD relay/solenoid state at start-up)

If your shifter switch makes the Arrow light go on and off, then the OD relay is working (although it could still be failing to control the solenoid voltage due to burnt contact points).

If Arrow light doesn't go on and off, start with the Fuse. If fuse is OK, suspect OD relay, shifter switch, or wiring to the relay—check for Key-On voltage at relay plug terminal 15 (blue and gray wires). If voltage is OK at 15, check for voltage at 86 (gray) when shifter switch is depressed. If 15 and 86 check OK, the relay is bad.*

Otherwise, the problem is most likely the white undercar wire from OD relay to Solenoid (#4 above) or the wire connector terminal at the solenoid. Less likely would be be Solenoid itself.

* NOTE: Relay wire & terminal info above is for 240. The 700/900 is not as easily tested due to relay placement.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.