Navigation Speed Sensor Help

[Vortec4800]

Well I got a Navigation system I'm going to install, and it needs a wire hooked into the speed sensor. I found the wire that the factory nav unit uses, but I'm not sure if it will fit the requirements.

I need a wire that does the following:

"This signal must be a 0Hz - 4kHz square wave pulse of less than 1.5V when the vehicle is at rest and from 5V - 16V when the vehicle is moving."

While I understand basically what this means, I have no idea if the wire in the car meets these requirements or how to even find out if that is correct. Can somebody verify what the wire in the truck reads?

 

[rando]

It just so happens I've been studying the SPD signal in our trucks in hopes of hooking it to my carpc. I'm trying to implement dead reckoning for my carpc navigation system. Presumably, that's what your aftermarket systems does with it too?

The SPD signal is at 0V when the truck is at rest and forms a nice 13.8V Pk-Pk (or whatever your battery/alternator voltage happens to be) square wave when the truck is moving. This is contrary to the information in the OEM shop manuals. They claim the signal is between 4.5-5.5V Pk-Pk max.

Based on my own observations (driving around in the truck with a scope hooked to the speed sensor), the frequency of the square wave appears to be approximately 1.1*(Speed in MPH) or 90% * Freq = Speed. This works out to roughly 15.84 inches per rising edge. You would have to drive 3600MPH to get a 4KHz frequency.

The best place to tap the sensor is at the junction block just behind the A/C controls. There is a bundle of wires there. Tap any of the violet wires with a red stripe.

 

[Vortec4800]

While I did in fact just go cross-eyed, I believe all that information translates to "yes that's exactly what you need".

Haven't taken any electronics classes yet, but they'll be coming soon enough...

It's interesting that the actual wire is so much different than what the shop manual claims it to be, I wonder why that is?

Anyway thanks for the help, its exactly what I was looking for!

It just so happens I've been studying the SPD signal in our trucks in hopes of hooking it to my carpc. I'm trying to implement dead reckoning for my carpc navigation system. Presumably, that's what your aftermarket systems does with it too?

The SPD signal is at 0V when the truck is at rest and forms a nice 13.8V Pk-Pk (or whatever your battery/alternator voltage happens to be) square wave when the truck is moving. This is contrary to the information in the OEM shop manuals. They claim the signal is between 4.5-5.5V Pk-Pk max.

Based on my own observations (driving around in the truck with a scope hooked to the speed sensor), the frequency of the square wave appears to be approximately 1.1*(Speed in MPH) or 90% * Freq = Speed. This works out to roughly 15.84 inches per rising edge. You would have to drive 3600MPH to get a 4KHz frequency.

The best place to tap the sensor is at the junction block just behind the A/C controls. There is a bundle of wires there. Tap any of the violet wires with a red stripe.

 

[rando]

It's interesting that the actual wire is so much different than what the shop manual claims it to be, I wonder why that is?

I wonder too. Either way, I can tell you for sure (at least in my truck) the wire I indicated peaks near 13.8v, not 5.5v.

Sorry about the techno mumbo jumbo. I was trying to give the best answer I could.