Vehicle Speed Wire [Archive] - Forum


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02-16-2012, 08:15 PM
Hey Folks,

I have a 2002 Grand Am GT... I am installing a radar system (long story, don't ask)... The radar system has a VSS wire that must be connected to the car speed sensor wire... It does not get any data from that wire regarding the speed of the car, it just gets a signal that the car is moving (which switches the radar from stationary to moving mode).

What would be the best wire to tap into for this? I saw on another posting someone mention the green/white wire going into the Cruise module? My GM dealer gave me the schematics for the wiring, and showed me where the low speed and high speed sensor wires are on the PCM... Sounds like a lot of digging to get at those wires under the dash.

What do you think?

02-17-2012, 08:14 AM
Yeah, tapping in by the pcm is pretty much going to be the best way to do it. That way you don't have to dig around in the engine bay. The vehicle speed comes from a sensor in the transmission, so the wire is going to be buried in the harness. If you take the PCM out then you can get to it right there and you don't have to run a wire through the firewall.

Vehicle speed signal output is the one I'd think you want to use. I don't know what kind of signal your radar system is looking for, but the VSS signal puts out a certain number of 5v pulses per mile to the cruise control to determine speed. When the car isn't moving there should be no pulses. It's pin 55 on connector C1 (the blue one) on the PCM, and the wire color is dark green and white. To get to it you'll have to take out a couple push pins and take the kick panel down. The PCM sits vertically in a plastic bracket under the dash, and the connectors are on the bottom. There is a bolt in the middle holding each one to the pcm. Loosen that and you should be able to pull the connector out.

There are some plastic covers over the back of them that shields all the pins and individual wires. You can release the tabs on them with a couple small screw drivers and pull the covers off so you can see the wires. The back of the connector has numbers molded in the plastic at the corners. 55 will be in the top left row between 41 and 60. Count your way over and find 55 and make sure the wire color is right, then tap into that one.

Be careful if you use one of those clamp on wire splices. I've seen people use the wrong size before, or they just don't fit well because they are designed for a range of wire gauges (ie 18-22), and you either don't get any signal or actually cut the wire you are tapping into and get an intermittent signal. I personally don't like to use them. I take a hobby knife and carefully peel back 4-5mm of insulation around the wire so I have bare wire, then I strip some insulation off the end of the wire lead I'm using and wrap it around the bare wire. I then put a dab of solder on the connection and wrap it with electrical tape. That way I've got a solid connection with my wire lead coming off the main wire, and if I need to go back to stock I can just cut the wire and wrap some more tape around it, and there are no breaks in the original wire. :thumbs:

02-17-2012, 10:22 AM
1st, what's the deal with the radar??

2nd, does it absolutely need to transition from moving to stationary??
if not, fake the signal so it always thinks you're moving, but i dont know why it switches.

02-20-2012, 02:29 PM
Thank you Aaron! That is exactly what I am looking for!


02-20-2012, 02:32 PM
Actually, had another quick question... So can I assume that the green/white wire under the hood at the cruise module is the same green/white one under the dash at the PCM?

02-20-2012, 06:08 PM
Yeah, it should be the exact same wire. It would just be easier to tap into it under the dash rather than running another long wire through the firewall and all through the engine bay if you don't have to.

02-20-2012, 06:10 PM
Yeah, I agree... Thanks again!

03-02-2012, 07:55 PM
Ok, I have found a solution I need some advice on... I ordered a VSS cable from the manufacturer.. It plugs right in to the OBD II port and plugs into the radar... This is what is says:

The CAN/VSS Adapter is used to generate a Vehicle
Speed Sensor (VSS) signal in late-model vehicles.
The CAN/VSS Adapter queries the vehicle speed from
the vehicle’s computer through the OBD-II diagnostic
connector and generates VSS pulses for the radar.
This device works with all 2008 and later vehicles and
some vehicles manufactured as early as 2005.

So the question is... Do you think this will work? I havent gotten the cable yet, so I cant figure out for myself..

03-02-2012, 07:58 PM
Probably not. It says it's a CAN based system. Our cars do not use CAN based OBD2 systems. They weren't introduced into 2005 and later.

03-02-2012, 08:03 PM
Crud :(