4x4 low diagnosis

[96eb96]

I can't shift into 4x4 low. No GEM codes, because as you will see this could never be detected as a fault.

You can really start throwing parts if you don't check first...

There is a relay in the dash. That is commanded when the GEM sees

• Neutral
• 4Low on switch
• Foot on brake
• Speed <5Mph.
• ABCD shift motor position switches have to be set correctly (I think it is ACD) when in Auto.

If you don't hear a click, something above is not working.

The relay is a pair. It can command the motor clockwise or counterclockwise.
The transfer case motor has ABCD switches, that report position back to the GEM.

So I used Forscan and the GEM diagnostics.
You can see every GEM parameter above (there is an extensive list for 4x4).
There is even a bi-directional mode- you could manually control the clutch and the shift motor!

I noticed that my Neutral safety switch PID wasn't flipping when I shifted. All the other data was good.
I jumped that NSS pin on the GEM to ground, and it shifted.
So it is either a wiring issue or the MLPS on the trans. The MLPS has a special switch and set of pins just for this shift.

But you see why this can't throw a code? The GEM is sitting there thinking..this stupid driver didn't put his shifter in neutral!

 

[Pete Deering]

I can't shift into 4x4 low. You can really start throwing parts if you don't check first...
There is a relay in the dash. That is commanded when the GEM sees Neutral, 4Low on switch, Foot on brake, and speed <5Mph.
Also, the ABCD shift motor position switches have to be set correctly (I think it is ACD) when in Auto.

If you don't hear a click, something above is not working.

The relay is a pair. It can command the motor clockwise or counterclockwise.
The transfer case motor has ABCD switches, that report position back to the GEM.

So I used Forscan and the GEM diagnostics.
You can see every GEM parameter above (there is an extensive list for 4x4).
There is even a bi-directional mode- you could manually control the clutch and the shift motor!

I noticed that my Neutral safety switch PID wasn't flipping when I shifted. All the other data was good.
I jumped that NSS pin on the GEM to ground, and it shifted.
So it is either a wiring issue or the MLPS on the trans. The MLPS has a special switch and set of pins just for this shift.

I have the same issue on my 1995. What is the MLPS? I am having problems with neutral safety switch on and off. Working fine now. I replaced the gem module no change. I was thinking it was corrosion in the shift motor. When I first started to have the problem it work and it did not work. Its not working now.

 

[96eb96]

I have the same issue on my 1995. What is the MLPS? I am having problems with neutral safety switch on and off. Working fine now. I replaced the gem module no change. I was thinking it was corrosion in the shift motor. When I first started to have the problem it work and it did not work. Its not working now.

Manual lever position switch/Neutral Safety Switch/Trans Range selector. The tricky thing is that the PCM gets a different version of the signal. So if you monitor the PCM PID, it shows the right position. That is why you need a service manual and real scan tool.

It is on the drivers side of your transmission.

Note "Electronic Shift Control"

Pin 8 could be the issue:

 

[96eb96]

Did more testing. The switch may not be the problem, still diagnosing. The switch terminals are in bad place making it difficult to test directly. On the Explorer, it is not a common failure point. It is on some other vehicles. Usually they fail with other symptoms (transmission related).

In order to notify the GEM of neutral, the switch must connect the below two circuits:
Circuit 463 in the connector above is good. It goes to the GEM.

Circuit 57 above goes from the connector above, to the firewall (see G201 in the diagram below). It is then grounded. It makes a full trip back to the GEM. This test failed.

You will see two black wires come out of the harness, they meet in a crimped connector, and are bolted to a stud.

I found that connector to be extremely crusty. The ground wire was so corroded it is difficult to strip. Going to pursue that next.

There is also no continuity to ground from Pin 5 in the diagram above.

 

[Pete Deering]

Did more testing. The switch may not be the problem, still diagnosing. The switch terminals are in bad place making it difficult to test directly. On the Explorer, it is not a common failure point. It is on some other vehicles. Usually they fail with other symptoms (transmission related).

In order to notify the GEM of neutral, the switch must connect the below two circuits:
Circuit 463 in the connector above is good. It goes to the GEM.

Circuit 57 above goes from the connector above, to the firewall (see G201 in the diagram below). It is then grounded. It makes a full trip back to the GEM. This test failed.

You will see two black wires come out of the harness, they meet in a crimped connector, and are bolted to a stud.

I found that connector to be extremely crusty. The ground wire was so corroded it is difficult to strip. Going to pursue that next.

There is also no continuity to ground from Pin 5 in the diagram above.

View attachment 324174

Thank you for the information. A lot of my ground wires are crusty or broken. When I find then I replace them.

 

[96eb96]

Thank you for the information. A lot of my ground wires are crusty or broken. When I find then I replace them.

It fixed my problem. I repaired the harness. 4x4 low shifts nice and smooth. Just changed the tcase fluid too.

Now I'm working on some door ajar switches that keep the lights on :lol:. Forscan said my liftgate (there are 3 switches in there).

 

[Pete Deering]

Did more testing. The switch may not be the problem, still diagnosing. The switch terminals are in bad place making it difficult to test directly. On the Explorer, it is not a common failure point. It is on some other vehicles. Usually they fail with other symptoms (transmission related).

In order to notify the GEM of neutral, the switch must connect the below two circuits:
Circuit 463 in the connector above is good. It goes to the GEM.

Circuit 57 above goes from the connector above, to the firewall (see G201 in the diagram below). It is then grounded. It makes a full trip back to the GEM. This test failed.

You will see two black wires come out of the harness, they meet in a crimped connector, and are bolted to a stud.

I found that connector to be extremely crusty. The ground wire was so corroded it is difficult to strip. Going to pursue that next.

There is also no continuity to ground from Pin 5 in the diagram above.

View attachment 324174

What is the MLPS? What does that stand for?

 

[Pete Deering]

It fixed my problem. I repaired the harness. 4x4 low shifts nice and smooth. Just changed the tcase fluid too.

Now I'm working on some door ajar switches that keep the lights on :lol:. Forscan said my liftgate (there are 3 switches in there).

So what the cause of the 4x4 low not to shift or engaged? What is forscan?

 

[96eb96]

So what the cause of the 4x4 low not to shift or engaged? What is forscan?

That pigtail under the hood near the firewall was rotted. G201 in the diagram above.

Forscan is a free scan tool that lets you do dealer level diagnostics. You just by an obd adapter that cost between $15-80.
Most consumer scan tools are toys.
forscan.org

Unfortunately, I don't think your 95 can use it. Some 95 Fords could.

 

[Pete Deering]

That pigtail under the hood near the firewall was rotted. G201 in the diagram above.

Forscan is a free scan tool that lets you do dealer level diagnostics. You just by an obd adapter that cost between $15-80.
Most consumer scan tools are toys.
forscan.org

Unfortunately, I don't think your 95 can use it. Some 95 Fords could.
Thank you

 

[96eb96]

What is the MLPS? What does that stand for?

Best to read thru everything I wrote above from the top of the thread. It explains in depth. MPLS is the trans shift switch (manual level pos sensor).

 

[Pete Deering]

Best to read thru everything I wrote above from the top of the thread. It explains in depth. MPLS is the trans shift switch (manual level pos sensor).

I clean Off my ground stud.its was rusty. Also the connector. Reinstall no change. What fluid did you use in the tcase?

 

[96eb96]

I clean Off my ground stud.its was rusty. Also the connector. Reinstall no change. What fluid did you use in the tcase?

Did you remove the eyelet crimp and resplice/reinstall the wires? That is where the issue is. In that crimp.
I use what they say to use now - Mercon LV. You can use Mercon (regular Mercon, NOT V), or Valvoline Transfer Case Fluild.

 

[Pete Deering]

Did you remove the eyelet crimp and resplice/reinstall the wires? That is where the issue is. In that crimp.
I use what they say to use now - Mercon LV. You can use Mercon (regular Mercon, NOT V), or Valvoline Transfer Case Fluild.

No, just clean surfaces, thanks pete

 

[96eb96]

No, just clean surfaces, thanks pete

Crimp connects the trans switch to the gem computer, so that could be it.