O/D how does it work

Looking at the wiring diagram for the O/D circuit when you push the button it goes to ground and the light comes on. The ECU is tied into this circuit how does momentarily going to ground lock O/D off and on? Please help explain how that works! And does the engine need to be at a certain temp for O/D to turn off when button is pushed?

 

Overdrive on/off button?? Do any of the tacomas have this feature
Discussion in '2nd Gen. Tacomas (2005-2015)' started by Jreaka13, Jan 23, 2010.

 

The ECU is just going to look at that signal line. If it has voltage (you have the button pressed), it's OK to shift into the highest gear. If no voltage, don't shift into the highest gear. It's only a signal, the transmission will maintain its normal shifting points -- you are not "locked" into O/D.

 

I understand it doesn’t lock into O/D, it locks out of O/D and O/D light comes on. When I start the truck and push the button on the shifter the light comes on the when I release the button it goes out. Does the truck need to warm up before it will stay in O/D off with light on tell button is pushed again to go back into O/D. And from looking at the wiring diagram I still don’t understand how it completes the circuit to cause light to stay on and O/D to turn off!

 

Maybe somebody will chime in ,but it sounds like you have a bad O/D Button

 

From a 1st gen owner's manual:

"Always turn the overdrive switch on for better fuel economy and quieter driving. If the engine coolant temperature is low or when the front drive control lever is in “L4” (low–speed position, four–wheel drive), the transmission will not shift into the overdrive gear even with the overdrive on."

 

Everything I’ve read says the O/D button is a momentary switch so it won’t stay latched.

 

This is how my '02 with the A340F trans behaves.

I have noticed that the fluid temps need to be above 80°F to shift from 2nd to 3rd. Once it goes to 3rd the OD on/off works normally regardless of temp. The trans only shifts to OD from 3rd gear. The button always turns the light on or off regardless of temp.

What year is your truck? Is it a 6 lug 4x4?

 

It’s a 2002 with a 3.4 V6 2wd automatic. If I start the truck and push the button on the gearshift the light comes on and if I release the button it goes out and won’t stay on.

 

It's a little hard to determine what your actual issue is.

The O/D light on the dashboard should illuminate when the O/D is OFF.

With the O/D OFF light illuminated, the transmission will not shift above 3rd gear. Once you press the button again, I would expect the light to turn off on the dashboard, and the transmission would be able to shift into O/D / 4th gear.

Here are the Owners Manual pages:

 

On an 01, which is probably the same, it looks like the switch is not momentary, so the ecu doesn’t latch the od lock, that is done mechanically by the switch itself.

I suspect you have a bad switch. Maybe tape it down and see if it stays out of od

 

I haven’t looked at the diagrams…..yet.

But the O/D off light should come on and stay on when you press the button. I don’t believe it is momentarily. I think it’s a latching relay, the relay will “unlatch” once the ignition is turned off. Or you press the O/D button again.

Again, I have not looked at the diagrams.
But that’s how I remember my 99’ working.

 

Looks like the switch just grounds out an input on the ecu

 

Not that is makes any difference.
But Toyota like to use pull to ground 0v.
I speculate that if one were to probe the ECM connection it would show 12v with OD on. And .5-0v with it off.

Again that doesn’t make a bit of difference.

I’m suspecting a bad O/D switch.

 

So it sounds like your truck behaves a bit differently than Digiratus.

If it is a momentary switch, it likely sends a "request" to the ECM to turn OD off, and the ECM decides what to do with that request. From the diagrams, that is what it looks like, no direct connection to the dash light. If it accepts the request, it leaves the light on or turns it off, depending on what the starting value was. One of those other lines coming out of the ECM likely goes to the dash light.

 

^ this

 

Yeah, the key here is whether it is a momentary switch or whether it is latched and has an actual off and on position. If it's just a momentary switch, it appears that it is working because the light comes on, at least temporarily. That means a signal is making it to the ECU, and the ECU is turning the dash light on. It's just not staying on.

 

This is consistant with what I am seeing on mine.

In playing around with it a bit today, the button's action does not indicate the button itself is latched. It is a single action button.

However, as @TnShooter indicated, pressing the button when the dash light is not on activates a latching relay that turns on the dash light, drops the trans back into 3rd gear and keeps that function engaged until the truck is shut off or the button is pressed again. Further, if the dash light in on, pressing the button releases the latched relay and allows the trans to shift into OD.

 

Looking at the diagram, though, wherever that latched relay is, it is energized by another output from the ECM, not directly connected to the switch itself. There are several other lines listed, not sure where those go (assuming at least ONE goes to the dash light).

Question for the OP, is it just on startup, or does it ever stay in the "O/D Off" state?

 

The dash light is powered by the 10A gauge fuse.
When OD is off, the ECM provides a ground for OD Off light. ( ODLP terminal of the ECM in the above diagram)