Speed Sensor

[microELVIS]

Thinking I need a new speed sensor, scan master wasnt registering over 30 mph last time to the track.

However the channles I am going through to get one asked me if its the front or back speed sensor. They're saying there are two speed sensors. Which one would it be ? Or is there just one speed sensor and they are looking at something wrong ?

 

[GNut]

Huh??

Front speed sensor?? Rear Speed Sensor?? I don't think so. The GN/TR Vehicle Speed Sensor is built into the speedometer cluster. It's a reluctor wheel/optical sensor setup. This info is transfered to the speedometer buffer, a little green box in the dash between the instrumnet panel and the radio. From the buffer, the signal is transferred to the ECM where the signal is used to control several engine and electrical functions including Cruise Control. If the speed sensor was bad, you'd get a check eng light and a code, and the cruise control would not work. A bad or faulty buffer might cause the problem you describe... but I doubt it. If your car was set up for the 145mph speedo conversion (worthless sticker!) and the trans speedo gear was changed that would most definitely cause a problem with speed readings from Scanmaster or any other scan tool. There is an external Vehicle Speed Sensor available that works very well with the GN/TR as I use them everyday in the GNX style replacement dashes I build. It will replace the speedometer cluster VSS but you still have to use the stock buffer box.


Tom Houser
Performance Instruments
www.gnxdash.com

 

[Black Car]

The only thing I can add to Tom commit is that you won't always get an error code.

Gary

 

[microELVIS]

The cruise control does not work and there is no error code.

Ill look further into the issue.

Thanks guys.....

 

[GNut]

The reason you're not getting an error is because there is a signal being transmitted although it is an incorrect one ("My Scanmaster shows 35mph"). If you had NO SIGNAL from the VSS, you would throw a code 24 in a very short distance. My best armchair diagnosis is the speedo buffer (little green box between the radio and instrument cluster). The speedo buffer is the same for non turbo cars and should be readily available in most any salvage yard. I also just thought of another remote possibility.. check the needle movement on the speedo for erratic behavior. It's a one in a million that the speedo cable is not functioning correctly (I'd check the gear at the trans while I was at it!) You mention no code but no cruise either...doesn't the vehicle have to be traveling at a certain speed to even activate the cruise?? Last point... Is this a new problem or one you've always had but didn't notice until you installed your Scanmaster?

Tom

 

[microELVIS]

I hadnt noticed the problem, so I couldnt tell you if its new or old. That night at the track, I had one run at 12.9 which the speed seemed to be working. After that it all dropped 13.20 13.30 13.50 . The speedo needle is slightly erratic but at very low speed, its fine once you get moving.

 

[dpok69]

Does this same info apply to digital dashes? Since i have owned the car it has not registered a speed over 40 mph. I had the speedo gears and the rear end checked by a TR tranny shop and they are correct.

I have seen the light green box near the radio under the dash. Maybe i will pull one out of the junkyard. If all else fails, i may be interested in that alternative vss sensor option.