Lets talk speedo

[nlfireguy]

I have searched, read, and worked on this for 2 nights now. I am an auto mechanic so I understand "lingo" and offering technical advice is perfectly fine in that I will understand it.
I have a 1998 Mazda B2500. 2X4 Manual 4 cyl. Purchased the truck with a cracked head, purchased another engine, runs awesome now with only 2 minor, but apparently tricky situations.
1) NO SPEEDO------ I have checked, and even swapped out VSS in rear axle (though I had no doubt it would not fix my issue). I have my scanner connected and have vehicle speed in my data and is accurate to GPS. I have No speedo, or odo. I took out cluster, supplied 1.2V to proper wires to motor and the speedo motor functions fine jumping it direct to motor. Where do I go from here??
2) Pass Airbag switch OFF light will not work, and I have a fault code reflecting this issue. Have yet to run down how, or possibly why my pass airbag on/off switch seems to not function.....

Fire away when ready, I am all ears

 

[adsm08]

Well the speedo issue seems to be a wiring problem from your description. I would start doing load and continuity tests.

The only other thing with that, I think the signal is relayed to the IC and PCM by the ABS module.

The PAD light is a common issue. The bulb burns out.

 

[kimcrwbr1]

+1 get some good wiring schematics and start looking for short and breaks. Pull all the connectors you can find apart and clean with electrical cleaner and use some dielectric grease to put them back together to protect from moisture.

 

[nlfireguy]

Well the speedo issue seems to be a wiring problem from your description. I would start doing load and continuity tests.

The only other thing with that, I think the signal is relayed to the IC and PCM by the ABS module.

The PAD light is a common issue. The bulb burns out.

I have a complete wiring schematic and it appears that the 2 wires from rear axle speed sensor "split" going to the GEM and RABS modules both. My main issue is I dont have access to the output, signal wire data as to what it should be. If I knew what the sensor generated in the form of a signal (ie volts) to GEM and RABS I then could figure out if I have proper signals to them both, then possibly check signal output from both.
I have been an auto mechanic in large shops for 21+ yrs, but recently retired and downsized to a small town tire/lube joint. I have my own snap on solus but miss the important information system I was used to having.

 

[adsm08]

Rear speed sensor just generates a variable AC voltage signal that increases with speed registered.

 

[nlfireguy]

Rear speed sensor just generates a variable AC voltage signal that increases with speed registered.

the A/C signal goes to the GEM?? Then from the GEM to PCM or where?? Wiring diagram is not very helpfull. It shows from rear sensor to GEM and RABS but I read data from engine controller and it shows the accurate mph on my solus. Wiring diagrams are not helping much. I cannot read a signal analog, or digital AC or DC even coming out of rear sensor. I know it has to have output or how else could I show mph in my pcm data???

 

[kimcrwbr1]

Does the pcm send the signal to the speedometer why is it stopping there. Does the cruise work?

 

[nlfireguy]

Does the pcm send the signal to the speedometer why is it stopping there. Does the cruise work?

It does not have cruise. I dont know if the pcm sends signal. Dont know where signal comes from. Wiring diagram shows it coming from 2 modules and pcm at the same time....everything I read states the raw signal goes to the 4 wheel control module (which I do not have) then to PCM....Nothing about rear wheel abs

 

[crazypj]

I'm a motorcycle mechanic but if speed sensor is magnetic it could be 'clogged' or shorted from metallic particle build up (haven't had one apart, does it 'count teeth' on crown wheel?)
Harley Davidson use transmission sensor off gear, if there is a problem there are no pulses generated (Suzuki did the same with cam position sensors for sequential injection)

 

[Earl43P]

RABS VSS goes to GEM and out on the GY/BK wire to PCM, Cruise and Speedo.

I can send you 2000, but I doubt it differs.

 

[kimcrwbr1]

http://www.youtube.com/watch?v=bPdPhGcZOe0
Maybe this will help

 

[adsm08]

Ok, VSS signal goes to the ABS module as an AC voltage signal.

The ABS module then relays a the VSS information to the IC, PCM, GEM, and SCS (if equipped), probably as a binary signal since it is moving over the HSCAN at that point.

 

[nlfireguy]

It has a bad Cluster. Picking one up tomorrow. I fixed the blown buld in the passanger airbag switch myself and repaired the airbag fault code. Bought a bulb from Radio Shack, unsoldered old one, soldered in new one...bingo works like a champ...Thank you everyone for the input.