Trans hard shift, speedo not working

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Nov 14, 2015 | 07:41 PM

cypressford

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Trans hard shift, speedo not working

Hello Ford truck enthusiasts!

Mine: 1997 Expedition 4x4 5.4L

Suddenly my speedo stopped working and the trans is shifting late and hard.
I have replaced the VSS on the rear diff; no change.
I have yet to find any sign of abrasion along the length of the wires hooked to it.
I'm wondering if this VSS is fuse protected - can't find mention of it in the owners manual?
Also wondering if there should be continuity across the two connector posts of the VSS with ignition off, on or engine running?
Thanks for any help!

Nov 14, 2015 | 07:56 PM

Mark Kovalsky

Frmr Ford Trans Engr

Joined: Aug 1999

Posts: 24,722

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From: SE Florida

Quote:

Originally Posted by cypressford

I have replaced the VSS on the rear diff; no change.

Then that's not it.

Quote:

Originally Posted by cypressford

I have yet to find any sign of abrasion along the length of the wires hooked to it.

That's nice. How does the wire inside the insulation look? Over the entire length? Just looking at the harness is less useful than cleaning the windshield. At least once you cleaned the windshield you've accomplished something. If you are not checking the wiring electrically you're just wasting time. That takes a meter and a wiring diagram.

Quote:

Originally Posted by cypressford

I'm wondering if this VSS is fuse protected - can't find mention of it in the owners manual?

There is no fuse in the circuit.

Quote:

Originally Posted by cypressford

Also wondering if there should be continuity across the two connector posts of the VSS with ignition off, on or engine running?

No.

You need to unplug the harness at the VSS and at the computer. Using your meter you need to check for continuity in each wire between the computer and the VSS, plus check each wire for short to ground and short to power.

Nov 20, 2015 | 01:29 PM

cypressford

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Got it. Thanks.
The computer is located inside pass side firewall, harness access in engine compartment? Known as the PCM?

Nov 20, 2015 | 01:53 PM

cypressford

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Now looking at a transfer case circuit wiring diag. from "Mitchell Repair Info Co". It shows Front and Rear Speed Sensors going to the GEM.

Nov 20, 2015 | 02:59 PM

Mark Kovalsky

Frmr Ford Trans Engr

Joined: Aug 1999

Posts: 24,722

Likes: 2,648

From: SE Florida

Quote:

Originally Posted by cypressford

Got it. Thanks.
The computer is located inside pass side firewall, harness access in engine compartment? Known as the PCM?

That's the one.

Nov 20, 2015 | 05:31 PM

pdqford

Logistics Pro

Joined: Jan 2001

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From: Central NYS

Quote:

Originally Posted by cypressford

I have replaced the VSS on the rear diff; no change.

The sensor on the rear diff is not the VSS. It is the rear axle speed sensor and is connected to the 4WABS module.

The VSS should be on the tail shaft of the transfer case.

Are you getting a code for the VSS?

Nov 20, 2015 | 07:07 PM

cypressford

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Quote:

Originally Posted by pdqford

The sensor on the rear diff is not the VSS. It is the rear axle speed sensor and is connected to the 4WABS module.

The VSS should be on the tail shaft of the transfer case.

Thanks for clearing that up.

Quote:

Originally Posted by pdqford

Are you getting a code for the VSS?

No.