I bought an 88 240 auto wagon a few months ago with 234K. The transmission is quite smooth and fluid is clean and full. However last week I began to experience times when the tranny would not shift into 4th gear when the 4th gear inhibitor is off, i.e. no illuminated arrow on dash. Note the dash light toggles as expected with switch presses. Another way of describing this is that cruising at 50MPH and pressing the switch has no effect on upshift/downshift and the engine sounds like it is working harder than it would in 4th gear (no tach on this car). It may be a little early to describe a pattern but it seems as if 4th gear is available when the car is cold and then becomes unavailable.
I found lot of discussion of this problem in old NG posts but I am looking for one diagnostic tip. Can I remove the relay and jump contacts in a way that would disable inhibiting 4th gear? If I still can't get 4th gear that would seem to isolate the problem to wiring from the relay to the solenoid, the solenoid, or the tranny itself. If I can get 4th gear that would seem to isolate the problem to the relay or perhaps even as some have suggested a fuse. One NG article claimed the relay consists of a single switch that sends voltage to both the dashboard light and solenoid when 4th is inhibited. If true that suggests that simply removing the relay should give me what I want.
RC