1998 4x4 5speed inop speedometer

[Mint12]

I recently bought my ranger about a month ago and one of the first things I noticed before buying it was the lack of a speedometer. There were some other small issues but those were solved pretty quickly. I've been looking through threads for a similar problem but nothing seems to be like what I'm experiencing.

The speedo threads I have read state that the needle will fail/work intermittently or will have other electrical issues tied in with the gem module. I have checked the vss ohm reading and it looked to be in spec. I even pulled a couple of them from pick a part to try but it hasn't changed anything. I checked for continuity in the wires from the sensor to the connector under the driver seat inside the frame and that checks out along with the conditions of the pins in the connector. I also bought a cheap data reading scanner and while on the highway I wasn't getting any data from the vss. Could it be a bad gem module?

My odo and speedo aren't something I absolutely need but it would be nice to have. If the parts are costly I might just buy a gps speedometer.

 

[RonD]

Welcome to the forum

Yes, in the 1998 to 2000 Rangers the rear axle ABS sensor was used for the Speed signal at the speedo/odo, computer and for cruise control

The rear axle ABS sensor produces 30,000ppm(pulse per mile) the Ford speedometer needs 8,000ppm
So Ford used the GEM module, in Rangers, to converter the signal for these 3 years, from 30,000ppm to 8,000ppm
In later years the Computer did this conversion but using an OSS sensor on the transmission.

If the computer was not seeing the 8,000ppm signal it would set code P0500 and turn on the CEL

So its odd you don't see a Speed signal on the OBD reader, and also don't see P0500 code

If you have Cruise does it work?

The rear axle sensor is a VR sensor, so it generates its own power, is sends out an AC volt signal .5 to 2v AC
The Sine wave of the AC volts is what is used not the "volts"
And it only uses the "+" side of the wave
So one of the wires at the sensor should show up as a ground, or close to it, 0 ohms to frame

The GEM module, behind the radio, gets the "+" signal on pin 9 then sends out the corrected signal on pin 1, to the computer, speedo/odo and cruise
speedo/odo share 1 signal wire

The ABS wires are spliced to share the rear axle sensors signal between ABS module and GEM
So no ABS light means the ABS module is getting the signal from the rear axle sensor
You can unplug the rear axle sensor and go for a drive just to confirm this
You should get an ABS light right away, because wires are unplugged

 

[Mint12]

I think the scanner may be faulty. I bought it specifically to check the O2 sensor data and it gave me nothing from all three. I realized that it may be a bad reader when I plugged in a snap on Apollo and it immediately showed a dead upstream O2. Now I'm thinking this data may be inaccurate because there was cruise control but I removed the steering wheel controls because they were damaged. Never tried cruise tho.

Yeah, and no cel for p0500
I'll try unplugging the sensor today

the .5v-2v and ground should be seen as the wheels spin correct?

Thanks for the response!

 

[RonD]

Yes, but meter has to be set to AC volts, and sensor is working if no ABS light

So you most likely have a bad connection at Cluster if no ABS light and no P0500 code(CEL light), so sensor and GEM is OK

If odometer works then speedo motor may be the issue

 

[Mint12]

Thank you

I'll check out the connector behind the cluster
If for whatever reason I am able to find and fix The issue, would the vss be able to generate the same signal with a Detroit locker instead of the stock diff?

 

[RonD]

Yes, shouldn't be an issue with detroit locker, you will use your current ring gear which has the ABS sensor's tone ring on the back of it
Picture here: https://www.supermotors.net/getfile/1022190/fullsize/tonering_3.jpg

You can see the tone ring behind ring gear, its just a press fit, the sensor "reads" each tooth as it passes by

Speed signal is a grey/black stripe wire at GEM, cluster, computer and cruise
Its at pin 1 on GEM(source), pin 58 on computer, pin 3 on Cruise and pin 1(center connector) on cluster

And as said, the speed signal uses the vehicle ground so just needs the 1 wire as the "signal", and you would have many other issues if these devices didn't have a good ground, lol, not just no speedometer