I searched the forum, but I'm still not finding the information I need. I have a 1996 4cyl 2WD Automatic. The speedometer works very intermittently, hardly ever. Using the OBD, I'm able to see the speed signal is not reaching the PCM. The ABS and brake lights are also on. I replaced the sensor in the differential (ABS) and the one at the transmission (VSS). Now my truck stays in 1st gear way too long until it eventually jerks into 2nd gear, at which time the O/D lights starts flashing. So, I cut the VSS ground wire near the plug and ran a new, dedicated chassis ground. My thinking was since the ABS and VSS share a ground, that connection must have been lost. Nothing changed. I have an extra gauge cluster which I changed out, just to rule that out completely, but I didn't think that would work anyway, since there's no mph reading at the OBD. What should I do next?

 

Welcome to the forum

In 1996 Ranger the speed sensor on transmission has no connection to rear axle ABS sensor, that was only in 1998-2000 Rangers

ABS system is a separate circuit, so is the ABS light off now, after new rear axle sensor was installed?

Speedometer and odometer share the one speed signal from VSS(on trans) but each has its own electric motor in the cluster
Is Odometer also intermittent when speedo acts up?

The VSS is gear driven, and these are nylon gears so can wear out, there is a DRIVE gear on the output shaft of transmission, it can get "cupped" so cause speed signal to be irratic
DRIVEN gear is the one that pulls out when VSS is pulled out, make sure it looks in good shape, you can often see the DRIVE gear thru the hole, mirror or camera shot
You can use a drill to spin the gear/shaft and see if speedometer reads normally at a steady drill RPM, can't remember if drill needs to rotate clockwise or counter clockwise, does NOT hurt anything to go opposite direction, you do that every time you back up, but it will not show Speed, just like when you back up, lol


Yes, both of these sensors are VR(variable reluctance) so generate their own voltage, AC Voltage, and only 1/2 this AC signal is used, so one wire on each is a relative ground. only the + side of the AC sine wave pulse is used
1997 RABS will be the same as 1996
The 2 rear axle sensor wires run directly to ABS module not grounded externally, so don't ground either wire, you can check the modules ground

In the 1996 instrument diagram you will see the VSS in the center with its wiring, the pink/orange wire is the ground, and its directly grounded

On the back of the Head in the engine bay there should be a Ground Strap that goes to the firewall, this is the Main Ground for all Cab Electrics
This is often left off after engine work, make sure it is there, or add your own new ground from engine to firewall, wiper motor bolt was a common ground point on firewall, or computer wiring should be grounded on firewall as well, you can use that bolt

 

The only logical solution left for the speedometer issue that I can see is the grey/black wire between the VSS and PCM is broken. But I think that might be beyond my ability today.
I have no idea what to do next about the ABS, but honestly I really need to fix whatever the problem is with the VSS first as it is severely affecting engine power and transmission shifting.
Thank you for your help so far.

 

The speedometer works! I put the old part back on with the new chassis ground and it works. The odometer still doesn't work 🤷🏼‍♂️

 

If BOTH Yellow ABS and Red Brake light are on then check that Packing brake pedal is up all the way, there is a switch on it that grounds the red brake bulb and ABS can't work with Parking brake on so it would also come on

And check the brake fluid level in the Master, there is a "low level" sensor on the Master, unplug its 2 wire connector and check it for corrosion

ABS system resets each time key is turned off, then at key on it should come on, Bulb Test, and then go off, if there is a problem with ABS sensor or module then it should take a few miles of driving for ABS light to come on again

If ABS light comes on with key on, and stays on, then its because red brake light is on

The VSS sensor's grey/black wire is spliced in a few places and runs to Speedo, PCM, GEM and Cruise(if so equipped)
If PCM doesn't see a speed signal it will set P0500 code and turn on the CEL(check engine light)
These devices just share the VSS signal, no interdependence in 1995-1997 Rangers
So if two devices, speedo and PCM, have no speed signal then wiring from the VSS would be suspect, or VSS gears

 

Well, the speedometer quit working again this afternoon. However, I am able to collect a freeze frame of data through the OBD app and it shows a constant value of 43 mph no matter how fast going. Every other data point collected and shown is also always the same. I think i may actually have a PCM problem??? Edit: I was wrong about what freeze frame did. It logs the parameters upon the first fault condition which could give a CEL. So that's why it didn't change when I refreshed.

On the ABS, yes both lights are on. I'll check out the switch under the pedal tomorrow. Fingers crossed.

 

Everything looks to be in order at the parking brake and master cylinder. Perhaps the actual switch is bad. That doesn't bother me nearly as much as the speedometer issue.
Speedometer working again this morning but still not the odometer 🤷🏼‍♂️ and I have zero faith it will continue to work.

 

And no P0500 code?

 

I think I must have/had multiple issues. Originally I had a P0500 code. Now there's no code. I can see the speed through the OBD but the speedometer itself works intermittently. The odometer never works and hasn't for years, even after replacing the gauges twice.

 

If speed seems correct via OBD2 then VSS/gears are working fine

1996 thru 2003 Ranger instrument clusters use same dimensions and wiring, so interchangeable
Tachometer is also pre-wired on all Rangers, plug and play

Speedo and odo use separate electric motors, but share the one speed signal from VSS, computer shares same signal as well, as does Cruise control

So the speedo and odo do rely on 12v and ground to work, in addition to speed signal
So you may want to test those wires at the connectors on the back of the cluster
In the diagram Fuse 25(7.5amp) powers the speedo full time, its not shared with other cluster instruments

 

Thank you! This information is super helpful!

 

Probably unrelated, but today the truck started acting strange on my way home from work. AC was blowing half speed even though the setting was high. A light on the dash, I think the airbag light, started flashing. And a series of beeps from behind the dash. Weirdly enough though, the speedometer was working 😂
Anyway, the darn truck shut completely off just as I was pulling into my driveway. It's hot as blazes here in Florida today so I haven't dug into it very far. But initially I'm thinking the alternator died. Put the battery charger on it and it fired up. I'm letting it fully charge before I go any further. Surely I wouldn't get so lucky as that has anything at all to do with the speedometer and odometer too.

 

Well the speed signal is AC voltage, 0.5vAC up to 8vAC
And an alternator generates AC voltage that is converted to DC Voltage
If a diode fails in the alternator it can Leak AC volts, called AC Ripple, and it goes into the vehicles electrical system, which causes all sorts of odd things in electronics

Google: Alternator Diode Check and AC Ripple Check

There is a 2:44 video, watch it, simple test

You can REV the engine during the test just to be sure AC volts stays low

Do the DC test as well

 

Interesting!