4+3 Transmission Question

[CharlesBrown]

I'm told there is a relay in the subject transmission that prevents it from going automatically into overdrive unless a certain engine temp. is achieved. If so, please tell me where this relay is located and what it's called. My search,here, brought up tons of usless info. Thanks

 

[Hib Halverson]

Have you looked for the information in the factory service manual?

 

[CharlesBrown]

Have you looked for the information in the factory service manual?[/QUOTE
Yes! Now I'm not saying it's not there, but have the writers of these manuals ever heard of an alphabetical index? Well the 1988 FSM sure doesen't have one. In the one I have you need detailed knowledge of the car just to find a part. If I had that knowledge, I wouldn't need to ask this question.

 

[vetteoz]

there is a relay in the subject transmission that prevents it from going automatically into overdrive unless a certain engine temp. is achieved.

All O/d operation is controlled by the ECM through said relay.
There is a Min engine operating temp programmed in the tune that the ECM will not engage below
Unless this temp or greater is indicated to the ECM , it will not turn the O/d on
Setting varies by year.
For 88 min operating temp is 122F

O/d relay is on firewall next to fuel pump relay

 

[rayquayle]

My search,here, brought up tons of usless info. Thanks

No more useless than what you've been told! There is no relay that prevents it from going automatically into overdrive unless a certain engine temp. is achieved. There is an OD relay on the firewall.

But it is under control of the ECM. It is true that the ECM will not allow OD engagement until a certain engine temp is reached, but to say that it is the relay that performs this function is misleading. Here's the schematic.

 

[rayquayle]

Oops, OZ beat me to it. Never mind!

 

[vetteoz]

If you are having O/d problems need to follow through the wiring circuit ( from the FSM ).
Now very common with age to have bad connections that prevent voltage getting to O/d solenoid in unit
If O/d light comes on , it shows ECM is "trying" to operate the unit; problem may be with wiring downstream of relay.

 

[vetteoz]

Oops, OZ beat me to it. Never mind!

Great minds think alike , Ray

 

[rayquayle]

Great minds think alike , Ray

Not so great, in my case, but I'm with ya mate!