Bronco Forum - Full Size Ford Bronco Forum banner

1 - 20 of 21 Posts

·
Registered
Joined
·
946 Posts
Discussion Starter · #1 ·
Well, I was coming home from work today and the speedo needle just dropped and the tranney came out of overdrive. I have had this happen before and all I had to do is thump the front of the instrument cluster and the needle work just jump up to speed and the tranney would go back into over drive. Today of course thumping, hitting and yelling did not fix it. I got home and pulled codes and there wre none. I checked all of the fuses and I am going to Ford to pick up a VSS in the morning. Is there a way to test the sensor? I don't think it is the vss. I think the speedo itself is bad.Can the speedo it self go bad? I pulled the cluster out and I do not know which wire goes controls the speedo its self. Am I right or can some one tell me what to do next. Oh, I did a search and did not find any help. I like the search feature myself it keeps me from haveing to type that much.
 

·
Registered
Joined
·
565 Posts
does it move at all? if it moves some, then I pull the speedo gear out of the tranny and check for any missing teeth. If it doesn't pull out then i'm afraid this could be early signs of seeing the tranny maybe about to go?? not good man. :(
 

·
Registered
Joined
·
1,563 Posts
I would try replacing the VSS it is what controls your speedometer and its in the rear axle....it doesnt calculate it off the transmission....those are some signs that the VSS is bad...search on VSS and you will see more on it...
 

·
Banned
Joined
·
11,163 Posts
The sensor in the rear axle is the ABS sensor; '93-96 Broncos don't have a VSS, which would be in the t-case.

Yes, PSOMs are notorious for going bad, but there are people who can fix them. I'd just go shopping in the junkyards & buy a whole '92-96 cluster, & swap PSOMs. Read this thread for more info.

.
 

·
Registered
Joined
·
946 Posts
Discussion Starter · #6 ·
well let me tell you this, the NAPA store did not know what I was talking about when I said vss. It took some time and he told me it was called a ABS sensor. So, if anyone had a problem finding a vss for a 94-95 this may be why. I did not know it was a ABS sensor. I heard it called vss on here all the time.:histerica
 

·
Never ending project
Joined
·
1,084 Posts
The sensor in the rear Axel are both a vss and abs signal generator depending on the year and model of ford some fords have a signal generator on the speedo cable at tcase it can get confusing it all depends what equipment the truck has.:thumbup
 

·
Banned
Joined
·
11,163 Posts
The signal it puts out can be used to read vehicle speed, but he's not asking about the signal. It's the sensor. The sensor's ORIGINAL purpose was for ABS, so if you ALWAYS call it an "ABS sensor", it will STOP being confusing for anyone. ;)

 

·
Registered
Joined
·
946 Posts
Discussion Starter · #9 ·
Well I have replace the whole insturment cluster and the vss/abs sensor and my speedo still does not work. I my tranney still goes into "limp mode" when I try to drive it. I am running out of ideas. I was sure it was the speedo due to the fact that I could thump it and it would start working again. I guess this has nothing to do with that. Could the RABS module keep it from working? How does the signal from the rearend make its way to the speedo?
 

·
Banned
Joined
·
11,163 Posts
Turn the key off, hold the RESET button on your speedo, & turn the key on. Release RESET after ~4 seconds, look at the display, & then turn the key off. Post what you see.
 

·
Banned
Joined
·
11,163 Posts
Good. The PSOM is probably working right.

Test continuity of the 2 ABS sensor wires (LG/Bk & R/Pk or maybe LG/R) from the rear diff all the way to the 4WABS controller behind the L headlight. Resistance should be under 5 Ohms.

If the wires are good, put the rear axle on jack stands, & hook up a digital multimeter (one that reads frequency) to the RABS sensor (disconnected from harness). The signal frequency should increase smoothly as the rear wheel speed does. Let the engine idle in gear so the wheel speeds stabilize, then measure frequency & voltage (at the millivolt range) of the sensor.

From the CD:
> Disconnect the rear axle speed sensor connector at the rear differential.
> Allow rear wheels to spin and stabilize at engine idle speed.
> Set the Digital Multimeter to the frequency counter (Hz) setting. Measure and record the frequency between the two pins of the sensor component connector.
> Change the meter to the AC mV setting. Measure and record the voltage output between the two pins of the rear axle speed sensor.
> Determine the rear axle speed sensor output in mV/Hz:

Output -- AC Voltage/Frequency

NOTE:
Measurements of BOTH the frequency and the voltage output must be taken. The actual speed the wheels are turning is not important -- the result of voltage output divided by the frequency will not change with wheel speed. However, it is crucial that both the frequency measurement and the voltage measurement be taken at the SAME wheel speed.

Sensor output should be greater than 6.0 mV/Hz.
 

·
Banned
Joined
·
11,163 Posts
InkDawg said:
...the CD calls it a Rear Axle Speed Sensor...
Yep, and on the same CD for the same application, it's called a VSS, a RABS, and an ABS sensor, and probably a few other variations. Confusing, huh? ;) Better to stick with "ABS", right? :toothless
NDIXIE said:
is the 4WABS inside or under the hood.
Steve83 said:
...to the 4WABS controller behind the L headlight.
Try to check the whole wire at once from one end to the other. If it's bad, then check each connector. Both are at the firewall. The circuits go in thru C205, then turn right around in the harness & come back out thru C202.

If resistance is slightly high, then you probably just need to clean the connectors. Disconnecting & reconnecting them should be sufficient for another 5-10 years, but adding some silicone grease would be even better.

If a wire is open (infinite resistance), you can either try to find the break, or just overlay a new wire & splice it in at each end.

If everything looks good, check each wire for resistance to ground with only the 4WABS & ABS sensor connectors UNplugged. Both should be over 10KOhm to ground. If not, find the short or overlay a new wire.
 

·
Registered
Joined
·
946 Posts
Discussion Starter · #19 ·
Well I have checked every wire for ohm and all seems good.

If everything looks good, check each wire for resistance to ground with only the 4WABS & ABS sensor connectors UNplugged. Both should be over 10KOhm to ground. If not, find the short or overlay a new wire.

Are you talking about each wire or are you talking about the 4WABS and ABS sensor themselves?

Damn there is alot of wire in there. More than I want to see again. If I have or done everything you say to do, what then? Could the 4WABS be bad? How do I check it?
 

·
Banned
Joined
·
11,163 Posts
"Check each wire for resistance to ground" means the 2 wires for the ABS sensor. To check for short to ground, just put the meter's ground lead on a good ground, & check the resistance at each of the 2 wires. But the 4WABS module has to be unplugged before you do this, or you'll be checking thru it.

If they both have over 10KOhm to ground, AND the sensor passed the volts/frequency test, then the speedo is probably bad. I've never heard of a 4WABS module going bad, except on a truck that was struck by lightning. To find out, though, you could repeat the sensor output test AT the speedo connector. That would check the output from the 4WABS.
 
1 - 20 of 21 Posts
Top