98 Beetle Spedometer Problems

[mrgoomis]

Ok so I'm working on my friends car (98 VW Beetle, 2.0L Auto)

The speedo is fluctuating and becoming inaccurate when the car gets over about 45mph. The speed sensor was replaced once and it fixed the problem for about 2 days then right back to the same. (Someone else replaced the speed sensor) I figured I would give it a shot, replaced the speed sensor again and put the oring in this time. Works! (for about 20 minutes)...

I hooked up a tester and got capture readings from OBDII connection, captured readings seem to be way off and are about 5mph below what is read on the speedo, but thats another issue i suppose. Speedo said I was going about 40 when I was zipping past cars on the freeway

Since the tester readings are innacurate even right to the computer I presume it is not the cluster, but something causing the sensor to go bad?

I Am STUCK! Please help with any suggestions!

[hako]

Originally Posted by mrgoomis

Ok so I'm working on my friends car (98 VW Beetle, 2.0L Auto)

The speedo is fluctuating and becoming inaccurate when the car gets over about 45mph. The speed sensor was replaced once and it fixed the problem for about 2 days then right back to the same. (Someone else replaced the speed sensor) I figured I would give it a shot, replaced the speed sensor again and put the oring in this time. Works! (for about 20 minutes)...

I hooked up a tester and got capture readings from OBDII connection, captured readings seem to be way off and are about 5mph below what is read on the speedo, but thats another issue i suppose. Speedo said I was going about 40 when I was zipping past cars on the freeway

Since the tester readings are innacurate even right to the computer I presume it is not the cluster, but something causing the sensor to go bad?

I Am STUCK! Please help with any suggestions!

My book says:
To ckeck the VSS operation, backprobe the 2 wire terminals on the VSS connector using suitable probes. Connect a voltmeter to the probes and turn the ignition on. Hold the right front tyre steady and rotate the left front tyre by hand whilst watching the voltmeter. The sensor should produce a fluctuating voltage of zero to approx 5 volts.

Other than that it says that the VSS is triggered by a toothed rotor on the output shaft - could this be misalgned or somehow out of kilter and the VSS is not getting the trigger it needs? Good Luck anyway mate.

[mrgoomis]

I havent tried the probing yet, but I have a feeling that everything seems to be aligned because when I replace the sensor it works perfectly for a time.

Also it seems that if I take the sensor off now it has actually gone bad already, I think that I would still be getting 0-5 voltages because the speedo is still giving me a reading, just not a correct one...

Ill post again when I try the probing, Any other suggesting in the mean time?

[hako]

Maybe its the actual speedo head....below is a site that fixes them and seems to say that they are troublesome:
http://www.bba-reman.com/content.asp...uster_problems

[veedubmechanic]

Very common problem on the ag4 automatic transmissions. Its the sensor ring for the speedo inside the transmission on the differential. The differential is metal and the sensor ring is plastic. Over time, it gets brittle and the ring comes loose from the metal differential gear ring. You need to remove the differential from the transmission and replace the 30.00 plastic ring.

[Joey-D]

Just found out my ring was bad. My speedometer didn't work. Replaced three vss on the tranny and still didn't work. Replaced speedometer and still didn't work. Pulled the vss and gear out of the tranny and spun it by hand and my speedometer worked. veedubmechanic do you have a break down drawing of this repair or a step by step?