so, I Am trying to add a cruise control to my 96 geo prizm. I need to find the VSS (vehicle speed sensor) wire. I have the schematics and after much confusion and ripping half the dash out I found the ECU and it seems to be plug C9 , violet/white colored. Now, how can I be sure this is the right one ? How can I measure this IS the right plug ? Everything else (12v, brake light, etc) I can measure, but the VSS is supposed to work on 4000 ppm Same story for the TACH signal. Hope someone can help me out.
Check for continuity between the plug at the ECU and the speed sensor itself. The speed sensor is located on the transmission, it should look like a threaded cap with a couple of short wires sticking out, leading to a connector.
Um, this is for an '88 Supra. You have to pull the combo meter and look for test points. With an ohm meter set to resistance measure the test points for the speed sensor.
Maybe. If you car is electronic, the VSS may not be in the combo meter...
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I would also give my local Toy dfealer a car and ask them how to test the CKT.
Great idea. I might take it one step further.. I will probably hook into the wire coming from the speed sensor in the engine bay and use that for the vss signal. I see 3 wires, and I believe I need the red/yellow one ( there is a red/blue and a red/white)
If the cruise control computer uses the raw signal from the speed sensor (my guess is that it uses the raw signal and then you have to calibrate it somehow to translate the on-off signal to a speed signal) then you should be able to tape the wire in the engine bay. Keep in mind that the engine bay is a wet and hot environment and the tap is subject to corrosion. I would solder the connection and seal it with heat shrink tubing.
Well, I had to set it up to the ppm (pulses per minute) and it told me to take 4000. I plugged in the wire in the engine bay and it worked at the first trial !! woohoo. Well, it won't see much wetness here (arizona) but it will get hot in there so.. I might have to use something more solid. Thanks for all the help. most work was finding the wires. But it's working great. Keeps the car nicely at speed.. no fluctuations at all ! This is an audiovox model.
That works, but it makes it rather difficult to disconnect it as a troubleshooting method. Strip, solder, a squirt of RTV silicone sealer and then heat shrink works.
Myself, I'd use a Scotchlock female tab crimp on the vehicle harness, and a squirt of silicone inside right before crimping to seal it from the worst of the elements. (Or crimp it, then pop the lock on the cover, squirt, and close again.) Then you use an 'insulated' (shrouded) .250 male tab crimp to the cruise control computer. And another dab of silicone will keep the water out, yet leave it easy to disconnect.
When complete, use a small ty-rap to secure the new wires to the existing harness so nothing has an excuse to vibrate and break from fatigue. You'd be surprised how fast that happens, especially on an engine where it gets all frequencies of vibrations - it'll make like a tuning fork on one of them.
4000 works - now check the minimum and maximum engagement speed, and adjust that setting as needed... You really don't want the cruise control to be actuatable on surface streets, on the off chance you bump the "Resume" button at a stop and the car takes off like you slapped it on the rump. This is why factory cruise won't engage below
25 MPH.
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