I have a 92 diesel with auto trans and speedometer quite working. Anyone with ideas to troubleshoot ? VDO Gauge goes thru the steps for programing but I can't seem to be able to calibrate it as instructions say to do ? I bought a sender and gauge from Spartan and worked for about 1000 miles.

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Originally posted by bigcat:
I have a 92 diesel with auto trans and speedometer quite working. Anyone with ideas to troubleshoot ?

Are you telling us that this is a VDO gauge? Is it a digital display or a regular sweep style display like what was original? Is this a hall effect speedometer, magnetic impulse or is it controlled by the ECM?

Hall-effect has three wires controlling the speedometer (5 total wires)

Magnetic impulse has two wires controlling the speedometer (4 total wires)

ECM has one wire controlling the speedometer (3 total wires)

Based upon info thus far (and a hunch) I'm going to guess that this is a magnetic impulse. This "should be" what most Barth's diesel pusher coaches are so I'll give you the diagnostics for this.

On the back of your speedometer there is an 8 wire disconnect plug? Yes. The terminal plug for this is wired (gauge side)

8 7 6 5
4 3 2 1

This would be how it is wired by taking the speedometer out and looking into the back of the gauge. Gauge side.

If you were looking at the plug (plug side) it is wired

5 6 7 8
1 2 3 4

The plug is flat across the top (5 6 7 8) and irregular across the bottom.

Pin 3 is the ground
Pin 4 is key on hot 12 - 14 volts
Pin 7 is the 5 volt feed for sensor
Pin 8 is the speedometer pulse signal line

Then this is a magnetic impulse speedometer

(If pins 6 2 8 3 4 are used this is a hall-effect speedometer. If just 3 4 8 are used then it's an ECM controlled speedometer)

Still with me? Test voltage with a volt gauge. Test pins 3 & 4 should be between 12v and 14v (battery voltage) if not then fix this first.

Test pins 7 & 8 by leaving the black test wire on pin 3. Have a helper drive the coach forward or backwards 4 feet while testing pin 7 & 3 (while pluged into the gauge) then try pins 8 & 3. With pin 8 & 3 the voltage should go up and down from 0v to 4v (0v 4v 0v 4v 0v 4v etc) If you get a steady 4v or 5v then the sending unit is bad. If you get the voltage to jump 0v 4v 0v 4v then the speedometer is bad.

7 pin should be a steady 5v. 8 pin will fluctuate. If both 7 & 8 stay at 5v (keep 3 pin as ground) replace the speedometer sending unit. If you get one side reading 5v and the other side reading 0v 4v 0v 4v while testing replace the speedometer.

Lets say pin 7 or 8 has 5v on one side and nothing on the other. Jump the two wires together at the transmission. You should now have the same voltage at both terminal 7 & 8 (keep test probe ground in pin 3) If not then you have a break in the wire.

Other things to consider. The magnetic pickup could have metal flakes stuck to it. It may be an indication of other problems.

Remove the sensor and check for metal flakes. At this point you could take a metal wrench and wave it over the magnetic end of the sending unit to see if the speedometer reacts or the 0v 4v 0v 4v is noted.