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huntingdeer
Novice
Nov 7, 2013, 4:30 PM
Post #1 of 9
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ford explorer no 4x4
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I have a 97 ford explorer with the 4.o sport trac xl 4x4.
The auto dont work and and the hubs dont lock.I have replaced the gem and done the brown wire mod.But now i want to to work like it should stock.what would be next? or what should i test to see what is bad.The transfer case clutches are good.How i know auto dont wonk is because i went up a hill today and the rear tires spun and i was not moving.I flipped the switch and it went up the hill.(switch to lock the hubs) Ive did alot of wire testing and only one wire is hot on the tod relay.It is blue/black.what makes the tod work or could a sincere make it not power the brown wire to lock the hubs. No lights flash in the dash.the lights work.
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Discretesignals
Ultimate Carjunky
/ Moderator
Nov 7, 2013, 6:02 PM
Post #2 of 9
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Re: ford explorer no 4x4
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Not really too familiar with this system, but looking at the wiring schematic, it isn't that difficult to troubleshoot.
The TOD relay gets power from the accessory delay relay on the light blue black wire with the ignition on or when the GEM energizes the accessory delay relay.
The TOD is basically a transistor that is controlled by the GEM to control the transfer case clutch. The GEM either grounds or sends power to the transistor base to turn the transistor on. The transistor then completes the circuit to allow power to go to the transfer case clutch. From reading the functional description it appears the GEM can control the duty cycle of the TOD, so that torque can be controlled between the front and rear wheels.
The only thing I am not sure about is if this transistor is pulled up or pulled down by the GEM to turn it on.
You know you have power to the TOD on the light blue/black, so all you have to check to see if the TOD is working is to take a test light connected to battery power or battery ground and probe the yellow wire with the circuit connected. If you see battery voltage on the brown wire when you do this, the TOD is functioning.
If you don't see 12 volts at the brown wire when doing the bypass test with your test light, you need to make sure the TOD has a good ground. If the TOD has what it needs, but doesn't function, the TOD is at fault.
If the TOD is functioning, the GEM might not be commanding it for some reason. From there you'll have to make circuit checks at the GEM to see if you have power, ground, input, and/or output problems.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 7, 2013, 6:07 PM)
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huntingdeer
Novice
Nov 7, 2013, 6:26 PM
Post #3 of 9
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Re: ford explorer no 4x4
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ok im a little confused haha what do you mean bu this or the word probe it(so all you have to check to see if the TOD is working is to take a test light connected to battery power or battery ground and probe the yellow wire with the circuit connected. If you see battery voltage on the brown wire when you do this, the TOD is functioning.) I have hooked up the test light to a ground and checked the wires.The one one has + power is the blue/black with the tod plugged it.What do you want me to do with the yellow wire?
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huntingdeer
Novice
Nov 7, 2013, 6:43 PM
Post #4 of 9
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Re: ford explorer no 4x4
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do you mean probe the brown wire? not the yellow?
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Discretesignals
Ultimate Carjunky
/ Moderator
Nov 7, 2013, 6:53 PM
Post #5 of 9
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Re: ford explorer no 4x4
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Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Discretesignals
Ultimate Carjunky
/ Moderator
Nov 7, 2013, 6:55 PM
Post #6 of 9
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Re: ford explorer no 4x4
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Use a 12 volt incandescent lamp circuit tester. DO NOT USE A JUMPER WIRE unless you want to fry stuff.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 7, 2013, 7:02 PM)
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Discretesignals
Ultimate Carjunky
/ Moderator
Nov 7, 2013, 7:51 PM
Post #8 of 9
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Re: ford explorer no 4x4
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I am not sure if the 12 V test light should be connected to battery pos or neg because I am not sure if the signal circuit (yellow) is pulled up or down to make the transistor operate. The only way your going to know is if you unplug the TOD and take a measurement on the yellow wire. The GEM has to be working of course and being told to operate the TOD. If there is voltage on it, the circuit is a pull up. The other way is pull down which means the GEM grounds the signal circuit to turn on the transistor.
Think of it this way:
The transistor acts as a faucet. The faucet is connect to a water supply tank. The valve on the faucet controls the amount of water that comes out. The water comes out the spigot of the faucet when the valve is opened.
The transistor is connect to a power supply (battery) at the collector. The GEM turns the valve (base) on the transistor to allow supply current to flow through the transistor and out the spigot (emitter).
The GEM opens the valve by sending a small amount of current to the base.
If this is a pull up circuit that turns on the transistor, you will see 12 volts at the brown wire when you touch your test lamp connected to battery positive. The ignition has to be on, of course.
If it is pull down, you will see 12 volts at the brown wire when you touch the test lamp connected to battery negative.
I can't get any more layman than that. You need a fundamental understanding of how DC circuits operate to be able to troubleshoot this.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Nov 7, 2013, 7:54 PM)
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huntingdeer
Novice
Nov 7, 2013, 8:07 PM
Post #9 of 9
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Re: ford explorer no 4x4
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ok so try + or - with a test light on the yellow.Still connected test to see if the brown has 12 v if not switch connections and if still nothing the tod is bad.I appreciate your help.Ive tried many forums and this one is the most help.
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