Mexico

My 4runner is a 1990 v6 4x4 automatic pushing 275k. Runs great, no issues. I am a driver who constantly uses the O/D button when I'm driving anticipating hills and for passing cars. I use my O/D like a stick shift.

Problem: All of a sudden it doesn't work anymore. When I push the button on/off, I get no light in the dash and I get no answer from my tranny. So clearly it is "stuck" on, which is better than being "stuck" off . . . and I can live with this "problem" because obviously the truck is driving normal. However, it is super annoying and I miss being able to shift it.

It seems to me that this could be a fuse, but my investigation of the owner's manual and the online forums haven't yielded anything telling me how to troubleshoot this. I mean, it's not like it was malfunctioning or has slowly died . . . it's just all of a sudden non-functional.

The other forums on overdrive seem to be people that have trouble with function while the O/D button is working normal. I am 99% certain that my problem is the tranny just isn't being told to shift either because the button is now broke, or a fuse somewhere is out. Or if the light burns out on the dash, will that break the circuit and prevent it from shifting? I was thinking maybe the bulb burned out and that is like a fuse??

Thanks for any help.

rustypigeon

When you push the O/D off button, that closes a contact which grounds the OD pin in the ECU, and grounds the O/D Off light on the panel.

Even if the O/D Off light were burnt out, the ECU would still get it's ground signal, and shut off the O/D.

It sounds like you are not getting the ground signal, most likely a bad switch. Just unplug the electrical connector to the switch and check for continuity. If you can't get continuity in either switch position, you found your problem.

FlamingToast

^^^ this. I highly doubt its a fuse since its almost certainly not going to have its own fuse. If you haven't noticed anything else that stopped working at the same time bet on the switch being the issue. Like he said, when the ECU sees ground on the circuit it knows the button has been pressed and overdrive should be disengaged.

scope103

The schematic can be found here: http://personal.utulsa.edu/~nathan-b...34electron.pdf Rustypigeon described it well.

That page also shows the pinouts for the O/D switch, but it's just an SPST switch so the pinouts are trivial.

Mexico

Thanks for the replies, I'm headed out to the truck now. I ran through all the diagrams and schematics that were sent my way . . . the only thing that doesn't seem obvious is access to the switch which it sounds like people think is bad. Hopefully that is more obvious when I get in there, but if it isn't . . . please pass along the how-to in the event I'm back in here in 30 minutes unable to get to it. I'm thinking it should be straight forward though.

Again thanks and I'll post the results. Makes sense that if the ground went bad, there are probably other things using the same ground . . . and given no other symptoms.

I was also thinking maybe a wire has come loose somewhere too . . . I mean, she does have near 300k on her and I don't drive it on the highway all the time. The only rust on the body is where I high-centered the rig on a large rock pile under passenger-side door. Left a nice, gaping and bent dent under the door . . . so she gets rattled every now and again. Maybe a wire broke somewhere.

Mexico

I got the switch apart easily. I tested it by bypassing the switch and hot wiring the two wires together which I assume should complete the ground and activate the O/D off light. This did not result in anything working, so is my testing method okay, but the problem is elsewhere (not the switch), or do I need to buy an ohmmeter and measure the resistance in the switch?

ThatGuy1295

mexico? is that were you are?

rustypigeon

That would help. You don't need a very expensive multimeter, but I would look for a digital one. You can get nice ones for less than $25, and with it you can find out where your problem is.

If you bypassed the switch properly, (shorted the proper connector) and you still do not get a O/D off indication, you can assume that the problem is not the switch. You can use your multimeter to find out if the problem is "upstream" or "downstream" of the switch.

The connector to the switch should have a white wire with a black stripe, and a yellow wire with a green stripe.

The white wire with a black stripe should have continuity with ground at all times. Put your multimeter in the ohms function to verify this. It should read not more than about 1 ohm.

If your ground checks out ok, then you can assume the problem is upstream of the switch. One thing you can check is if you get the "ECT PWR" light when you push the ECT mode switch. This shares a common voltage source with the O/D off switch, and will help to pinpoint the problem area.