Hi all,

My Ranger is a 1998 with the 2.5, 2 wheel drive, auto transmission. O/D light flashes after about 10 minutes of driving and slips into a lower gear every now and then. It shifts hard sometimes, but sometimes it shifts just fine. The code it pulls is P0500- Speed Senor A.

My ABS light is not on and I have replaced the ABS sensor in the rear differential twice now. I know I do not have a speed sensor in the transmission because I have checked. I looked over the wires that lead from the ABS sensor to where they go inside the vehicle and everything appears just fine.

I just don't know what else to do or try besides taking it to a mechanic. Any advice for a new guy on these trucks? Would a vacuum leak have anything to do with it? I know I have a vacuum leak for sure because my heater switch (the part that switches from hot to cold air under the hood via a vacuum line) does not want to engage from the vacuum. Also, I have crusie control but it cuts in and out. I have vacuum cruise control.

Thanks much,

David

 

From 1998 to 2000 the Rear ABS sensor(VSS) wires were spliced and connected to the GEM module behind the radio.
The VSS generates its own electricity, AC current, but only one signal wire is used, the other wire is a ground reference, so if you test the wires at the VSS with ohm meter one should be low ohms to ground, then other wire goes to speedo/computer via GEM

So ABS still has direct connection to rear axle sensor, so no ABS light means sensor is OK, assuming ABS light bulb is good, lol.

P0500 means computer is not getting speed signal

The GEM module gets same sensor signal and converts it to the 8,000PPM that the speedo and computer expect.
So GEM is programmed at factory for stock tire size, axle ratio doesn't matter for rear axle sensor.
My guess is that either the wires going to the GEM or coming out of the GEM are disconnected.
Could be GEM is failing but it controls ALL the electrics in the cab, so there should be other issues.



Wiring seen below

 

Thank you! that makes a lot more sense and gives me more of a place to check for wires. I will tear into the space behind the radio and find the GEM and check the wires. My ABS light is working, I unplugged the connector to the ABS sensor and the light came on just to see if it worked or not.

The truck does have different size tires than when it came stock with I am pretty sure. It has 235/75/R15's all the way around. I will check on the GEM and report back.

One quick note I forgot to mention: I have given it a full fluids replacement whn I bought it. I replaced the rear-end oil, motor oil, and just recently transmission oil and filter.

Thanks again

 

I checked the GEM, everything is still plugged in.

 

If you can jack up the rear wheels, and BLOCK the front wheels you can test for AC volts, while rear wheels are spinning, at the GEM in and GEM out
Depending on wheel speed idle in gear should be almost 1 volt IN, slightly less out.
That will tell you if GEM is getting VSS voltage and outputting VSS signal
Set volt meter for AC volts, black to Ground, red to VSS wire you are testing

 

Okay, it may be a while until I can do that. I am in college currently, but I will see what I can do. If I can I am going to have the auto mechanic students take a look at it and see what they can come up with.

Thanks for all the help!

 

Yes, it is hard to test this

You can also do continuity test on the wires.
You need a long wire to reach from rear axle VSS to GEM in cab

An OHM Meter set to lowest OHM setting will show 0 ohms when you touch it's probes together, 0 ohms means no resistance, a "short", or full continuity, a good connection

Test the long wire first, to make sure it has good continuity, touch a probe to each end of the wire, may be some resistance but should show low or 0 ohms, this depends on the meter itself

Disconnect VSS wire from the sensor, connect one end of the test wire to either VSS wire, run test wire into the cab
Then in the cab touch one probe to the test wire and then other probe to a Ground, bare metal in Cab, if 0 or low ohms then that VSS wire is the Ground side and it has a good connection to Ground
If high ohms or N/C(no connection) then take probe off ground and touch it to the Pin 9 wire on GEM plug, IN from VSS
It should show 0 or low ohms if wire and splices are OK

Test other VSS wire the same way

One should be a good ground and the other a good connection to pin 9 at GEM

 

UPDATE

I took my truck to the Ford dealarship in Marquette here and they managed to fix the O/D light blinking and shifting issue. The mechanic narrowed the speedometer issue down to the cluster so I am going to replace that and see if that works now.

Thanks

 

What ended up fixing your O/D light blinking? Having very similar problems in my 01'. Throwing a P0741 and P0500 code right now.

 

Hi, the O/D light ended up getting fixed by whatever the mechanic did. I believe he replaced the wires leading from the transmission to the cluster and whatever electrical gremlins I am sure he found. After that, the shifting issues all went away. I replaced the cluster about 5 months ago with one from a 1999 Explorer, worked just fine.

Hope you get it figured out,

Dave