VSS testing

[Okiedokie]

Crosley or Wayne, Help. I am trying to diagnose a lack of "vehicle speed" reading on my scan tool. I have been having trouble programing my Autometer electric speedo and reallized that the scan tool always reads 0. The harness I used with my TPI has the connector for the VSS in the harness, and the speedo get signal from ECM. I read somewhere that the correct reading of resistance is 190 to 250 OHMs. Mine reads 410. The BVD unit I bought at Oreillys reads 380. How do I tell if the old one is defective or not. It is a 1990 Camaro 7730 speed density computer. When I follow the steps to program the speedo the final step that should result in the needle going to zero, it pegs to top. Joe

[Okiedokie]

Left out that it is a 700R4 transmission.

[enjenjo]

What brand of guages do you have? Is it supposed to work with a stock GM sender, or do you have an aftermarket sender.

There are two possible wave forms used on VSS senders. A sine wave, and a square wave. They don't always interchange. GM uses a square wave form. In addition there are different frequencys used, any where from 2000 cycles per mile to 16000 cycles per mile. Some aftermarket speedos will adapt to read all the different cycles, some won't. if the sender frequency is wrong, it can sometimes be fixed with a VSSB, a buffer to correct the frequency.

To test the sender, hook a multimeter set on 6 volts to the sender wires. Then put the trans in gear, and let the wheels turn at idle. The voltage should vary from 0 to 6 volts as the shaft turns. If there is no voltage, or a steady 6 volts, the sender is bad.

I have had new aftermarket sender that were bad out of the box.

[Okiedokie]

Thanks enjenjo. It is an Autometer. Yes it is supposed to work with either. Thanks for the tip on the 6 volt reading. I am using stock GM sender.

[enjenjo]

http://www.autometer.com/tech_faq_answer.aspx?sid=2&qid=70

[Okiedokie]

Thanks again, I could not find that. I try it.

[enjenjo]

I did make a mistake on checking the sender. Check it with the ignition on, engine NOT running, turn the rear wheels by hand.

[wayne petty]

to start with...  when i looked at the 90 camaro VSS..  i know this is NOT in a camaro...  i am still looking around for info..
i did notice that when VSS problems pop up.. that charts C1  C8 and C8a are called into play.. more to come as i look for copies of those..

i saw 5 different options at AZ...

the wells site lists them between 200 and 600 ohms..

this is not going to help much except for the bottom link that takes you to a PDF file..

Duralast/Vehicle Speed Sensor
Part Number: SU1013
Notes: Transmission mounted sensor. Sensor option label D9E. Driven gear 19, 20, 22 teeth
no image..


Duralast/Vehicle Speed Sensor
Part Number: SU1010
Notes: Sensor option label D9A. Driven gear 37, 38 teeth
http://www.wellsve.com/custom_searches/showpartimage.php?partno=SU1010

Duralast/Vehicle Speed Sensor
Part Number: SU1003
Notes: Sensor option label D8E, D8N
http://www.wellsve.com/custom_searches/showpartimage.php?partno=SU1003

Duralast/Vehicle Speed Sensor
Part Number: SU1024
Notes: Sensor option label D8G, D8M
http://www.wellsve.com/custom_searches/showpartimage.php?partno=SU1024

Duralast/Vehicle Speed Sensor
Part Number: SU1005
Notes: Sensor option label D8F, D8I
http://www.wellsve.com/custom_searches/showpartimage.php?partno=SU1005





i did also find this short tech write up on VSS sensors on various cars...  probably worth 10 minutes to read..

http://www.wellsve.com/sft503/counterp_v4_i2_2000.pdf

from some random sites..

1985-93 GM TBI not using factory buffer (DRAC) 2000 counts per mile..

1985-93 GM TPI Systems 4000 counts per mile..

Late model GM trans mount units 80000



some generic VSS testing info...

http://www.diycardoctor.com/vss_sensor.htm

[wayne petty]

waynes thoughts..  exactly what frank said...

look at output voltage from the VSS.. ON.. OFF.. ON  off.. as you slowly turn the drive shaft or rear wheels...

you will also want to look up CODE 24 section of the DTC pages..


Vehicle Speed Sensor

The Vehicle Speed Sensor (VSS) sends a pulsing voltage signal to the ECM which the ECM converts to a miles per hour reference. This sensor mainly controls the operation of the automatic transmissions Torque Converter Clutch (TCC) system and also provides an input for the GM electronic cruise control unit. On all Corvettes, and some of the later Camaros and Firebirds, this unit is mounted directly in the transmission extension housing, where the speedometer drive gear sleeve would have been and provides the VSS signal for the above inputs and also for the electronic speedometer. In vehicles that utilised a speedometer cable, the mechanism is a small unit mounted to the back of the instrument panel behind the speedometer and activated by the speedometer cable. In most Street Rod or similar installations this function is not required, unless you would be interested in having the TCC function totally as originally designed, or adapting a late GM electronic cruise control to the installation.

1990 - 1992 TPI ENGINES USE A 4-PULSE VSS.
THE 1985 - 1989 USES A 2-PULSE VSS

found a great resource at this link...

http://www.hotrodhandbooks.com.au/eBooks/TPI/IX.html

[Okiedokie]

Thanks for the help all, I found my VSS sender to be fine. It looks like the problem is in the way the harness is routed.

[wayne petty]

speed sensor wiring should be TWISTED pair..  probably 10 to 12 twists per 12 inches..

there is a specification on this.. so the 10 to 12 is a ROUGH GUESS...

does it have to be shielded???

next time i run across one or two of these.. i think i will crack them open and see what they do inside..

[enjenjo]

Not much there Wayne, a magnet and a crystal connected to wires. No moving parts. As the reluctor ring moves by, the magnetic field affects the voltage passing through the crystal.

[Okiedokie]

Back to making the speedo work. I have verified, by removing the VSS and chucking the shaft in a drill and spinning it, that the signal is good to the speedo, checked with a multimeter set on ac. With the VSS installed and rear end in the air and the engine spinning the rear tires, no signal. The drive gear on the output shaft appears to be ok and is centered in the hole. The driven gear is perfect. I'm lost as to why no signal? What am I overlooking?

[enjenjo]

Which transmission do you have? How large is the hole for the speedo drive, slightly over 1", or more like 3"? Can you get me the number of teeth on the driven gear?

[Okiedokie]

700R4, more like 3" hole, 39 teeth on the driven gear. Drive gear is more of a light green although all the info I could find said there are 4 drive gears, none green.