Speed Pulse Signal location 2003 Liberty LE?

[Rednroll]

Hi,
I have a 2003 Jeep Liberty LE 3.7L. I'm starting to do a complete audio system install. The head unit I'm installing is an OEM double din Navigation head unit. I just finished modifying my bezel to accommodate the double din head unit, so now I'm planning out my wiring needs.

I need to run a speed pulse signal to the Navi head unit to get accurate navigation. My vehicle has factory installed cruise control, so I'm assuming there must be a speed pulse wire running around some where within the vehicle that I could tap into and run to the head unit, since cruise controls usually require this type of signal. I did numerous searches looking for this type of information and the only info I have found so far is "Yes", there is a speed pulse signal. Can someone point me to a location inside the vehicle where I can tap into the speed pulse signal, so it would be easy to run a wire up behind the dash and to the navigation head unit?? A fuse block location? A wire in a certain location and the color?

 

[tjkj2002]

The speedo is operated from a sensor mounted to the top of the rear diff,just look on top of the center of the rear diff.It's the only 2 wires running to it,can't miss it.

Cruise control does not have use the speedo signal in the KJ.

 

[Rednroll]

I really can't wait to get this set up, off of my bench and into the vehicle.

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[Rednroll]

The speedo is operated from a sensor mounted to the top of the rear diff,just look on top of the center of the rear diff.It's the only 2 wires running to it,can't miss it.

Cruise control does not have use the speedo signal in the KJ.

Sorry, to show my ignorance here.....I'm an electronics geek. So when you mention vehicle stuff like "rear diff" my head starts to spin a little I'm not so bad though....I know where the "muffler bearing" is located......I'm thinking the rear diff is somewhere near the area of the rear axle and thus, a location outside of the vehicle??? Oh my. Can you give me a little more description of where the rear differential is located? If I can locate those wires and they run to the speedo, then Maybe I can follow the wires and find a place where they might run inside of the vehicle and tap in.

 

[tjkj2002]

Sorry, to show my ignorance here.....I'm an electronics geek. So when you mention vehicle stuff like "rear diff" my head starts to spin a little I'm not so bad though....I know where the "muffler bearing" is located......I'm thinking the rear diff is somewhere near the area of the rear axle and thus, a location outside of the vehicle??? Oh my. Can you give me a little more description of where the rear differential is located? If I can locate those wires and they run to the speedo, then Maybe I can follow the wires and find a place where they might run inside of the vehicle and tap in.

The rear diff is what your rear wheels are attached to.Those 2 wires run to the BCM which is located under the dash on the left side.I wouldn't tap in to those lines directly since it will effect the speedo,ODO,and how the trans shift.

By looking at the stereo you are trying to install the speed signal that the KJ has may not be compatible with that head unit.

 

[Rednroll]

By looking at the stereo you are trying to install the speed signal that the KJ has may not be compatible with that head unit.

Nahhhh....now you're talking my area of specialty. I have that part all figured out. YES....this is a MyGig RER head unit for a 2009 Liberty. YES, I know that with a 2003 Liberty, that this is not a direct drop in because the 2003 Liberty has a J1850 bus, and this radio requires a CAN bus operation like found in the newer Mopar vehicles and this would normally require the vehicle computer to turn it on/off via CAN communications and also the speed information is sent over the CAN bus.

What I've got is an external module that connects to this radio which accepts an ignition on/off signal and a speed pulse signal and then the module converts those analog signal inputs to the necessary CAN messages to turn the radio on/off and also give the vehicle speed to the radio. As you can see from the pictures this radio is powered on and functioning on a bench setup.....which obviously doesn't have a vehicle module to turn it on. Now I just need to locate a speed pulse signal.

The BCM inside??? Now you have my full curiosity....Do you know where I can find a picture where this BCM is located? I aint scared when it comes to tapping into wires and figuring out if those wires are carrying the correct signal I'm looking for. The type of speed pulse signal I'm looking for is a square wave pulse, where the frequency of the pulse gets higher when the vehicle speed increases.

 

[Rednroll]

Ok....you really helped me out. I was able to do some google searching based off of what you said, which brought me to a link, where someone else was looking for the same information.

http://www.the12volt.com/installbay/forum_posts.asp?TID=102944&KW=vss

I guess this is what I'm looking for, incase anyone else needs this information:

VSS (Vehicle Speed Sensor) is the Light Green/Yellow and located at C1 pin 20 of the BCM.

Now, I just need to look under the dash and figure out where the BCM is and find this Green/Yellow wire on Pin#20 of the connector.

Thanks for the help!!!....if anyone has any pictures of the BCM with a pin out diagram...that could be useful.

 

[Sir Sam]

Ok....you really helped me out. I was able to do some google searching based off of what you said, which brought me to a link, where someone else was looking for the same information.

http://www.the12volt.com/installbay/forum_posts.asp?TID=102944&KW=vss

I guess this is what I'm looking for, incase anyone else needs this information:

VSS (Vehicle Speed Sensor) is the Light Green/Yellow and located at C1 pin 20 of the BCM.

Now, I just need to look under the dash and figure out where the BCM is and find this Green/Yellow wire on Pin#20 of the connector.

Thanks for the help!!!....if anyone has any pictures of the BCM with a pin out diagram...that could be useful.

Sounds like you need BCM pinout information, I would look here:
http://colorado4wheel.com/allmanuals/Jeep/KJ/

 

[Marlon_JB2]

I dunno about a '03, but on my '04 and '06 the BCM was located next to the fusebox which is accessible on the driver's side of the instrument panel (Colloquially known as the dashboard).

 

[Sir Sam]

I dunno about a '03, but on my '04 and '06 the BCM was located next to the fusebox which is accessible on the driver's side of the instrument panel (Colloquially known as the dashboard).

yup

 

[Rednroll]

Sounds like you need BCM pinout information, I would look here:
http://colorado4wheel.com/allmanuals/Jeep/KJ/

After doing a little more digging, I think what I'm looking for now is the Junction Block pinout.

You guys seem to be correct, that the BCM is connected to the fuse panel on the driver's side dash, by the driver's door. It looks like the BCM plugs directly into a connector on the Junction block, thus there are no wires that tie directly to the BCM, it's just a straight connection of the BCM to the Junction Block. So I'm assuming the wires connect to the junction block, so I just need to figure out a way to get at the wires connecting to the junction block.

Here's a diagram I found in a service manual that shows the Junction block.....I just can't find the actual pin out information. I think I'm going to go with a leap of faith, that the speed pulse signal I'm looking for is on a Yellow/Green wire that ties into that C1 connector of the junction block.

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[Powerslave]

That links to the FSMs, which is against the forum rules, so I bookmarked it, before it gets deleted...

 

[Rednroll]

Ok, I did quite a bit of reading and probing around on different wires to finally find what I was looking for.

After doing a lot of searching on the internet for information, I found a lot of the information was either just too vague on being helpful enough, or was just wrong.

So I'm going to post where to find this speed pulse signal along with all the information you need. This speed pulse signal is required by a lot of NAVI radios, and you want to make sure you're getting the correct signal.

So here goes:

Location:
The Speed Pulse signal or also referred to as the VSS (Vehicle Speed Sensor) output can be found on the 26 pin connector, which plugs into the BCM (Body Control Module)

There are 2 Grey connectors which connect into the BCM. One is a 26 pin connector and the other is a 22 pin connector. There are 2 different speed pulses on each connector. For most NAVI radios, you want the one on the 26 pin connector.

Here is the pin out information that you need:

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[Rednroll]

Location of BCM
The BCM is located under the dash, on the driver's side. You can get access to the BCM and the 26 pin Grey connector by removing the trim panel directly below the steering wheel column. You can pull on the top part of the trim just under the steering wheel colum, and the trim piece will fold down on a hinge.

The BCM is mounted on the back of the terminal block. If you reach behind the terminal block, you will feel 2 wire harness connectors, which plug into the back of the BCM. The top connector is the 26 pin connector, and the one directly below it is the 22 Pin connector.

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[Rednroll]

Here is the correct connector and the SPEED PULSE wire. It is the Green/Yellow wire.

Front of Connector:

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Rear of Connector and Wire which carries Speed Pulse Signal:

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[Rednroll]

I put an O'Scope on the wire to verify the signal. Here is what that signal looks like, to ensure it is the proper signal that you are looking for. It is a 5Volt square wave pulse, which increases in frequency as you increase in speed.

Scope Pics of Speed Pulse Signal:

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[Marlon_JB2]

So does it work?

 

[Rednroll]

There is a lot of information on the internet and guides that say to use the GREEN/ORANGE wire. This is a Speed signal signal, but it's probably not the one that you want to use for a Navi radio. Just in case if your application calls this wire out, I will post the information.

The GREEN/ORANGE wire speed pulse is located on the 22 Pin Grey Connector, that connects to the BCM.

Here is the Pinout information for the 22 Pin Connector (Pin 21)

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Here is what that signal looks like
Notice it's a higher frequency square wave pulse which varies with speed and has a much smaller amplitude and a DC offset voltage.

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[Rednroll]

So does it work?

It should.....that's EXACTLY what I'm looking for......now I just have to move on to the next step which is wiring the Navi radio into the vehicle. I couldn't start the wiring without finding the speed pulse signal.

 

[JeepJeepster]

Wow.. thats alot of stuff Ill never need to know..