LoWeLL216

iTrader: (1)

I posted this in the audio / electronics section, but thought I'd ask here as well since it sort of applies.

This is actually a question concerning my wife's vehicle, a 2004 Mitsubishi Endeavor. Since those forums have such limited information I thought I'd post up here.

Here's my situation. I got a Clarion dvd/cd head unit along with a separate Clarion navigation unit. The audio installer hooked up the head unit which works fine. They hooked up the nav unit, but didn't connect it to the speed sense wire (which tells the nav unit how fast the vehicle is going and is required for the unit to track movement) on the PCM. After later tapping the speed sense wire my speedometer went dead and the nav unit still didn't track movement.

The installer is telling me the nav unit is bad and may have fried part of the vehicle's PCM. The vehilce hasn't thrown any codes. I didn't buy the unit from them and because of this they're telling me they are not liable for the "damage" it caused. (I agree with this IF the nav unit did in fact cause the problem)

Question #1 - Does the speed sense wire on the nav unit output any power or is it simply used to read the signal output by the PCM? It seems to me this is no different than connecting a gauge to read an output sigal and highly unlikely that this wire (or the nav unit for that matter) caused this.

I took the vehicle to a dealer to have it diagnosed and they tell me the PCM is fine and that it's most likely from a damaged wire. Basically, the PCM is outputting correctly, but the signal just isn't getting to the speedo anymore. They're not done working on it yet so the story may change, but this is what they think so far.

What I'm thinking is that the nav unit isn't bad, it just wasn't getting a signal (like the speedo) due to a bad speed sense wire tap that damaged the PCM wire. Does this seem reasonable or am I off base here? I do a fair amount of tuning on my Trans Am and have tapped a few PCM wires before to read various information, but have never worked on or installed a nav unit.

Question #2 - I know anything is possible, but is it very likely the nav unit could have done this or is the installer maybe trying to shift a little blame here?

Thanks in advance for everyones help!

caliswangin916

iTrader: (3)

does the navigation unit's instructions specify that a wire is to be connected to the speedo? i've never owned a nav unit so just throwing this out.

i do have gps for my laptop which tracks my speed by using the gps unit itself. so in my case, speed is communicated from satellites to the gps unit which woud be more accurate than relying on a car's speed sensor.

caliswangin916

iTrader: (3)

my bad...just did a google and got this: Vehicle Speed Sensor (VSS)
In addition to the standard power and ground leads, many car navigation systems connect to a vehicle's Vehicle Speed Sensor (VSS) wire. The VSS wire is used by the vehicle's cruise control to determine the vehicle's speed - it serves the same function for the car navigation system. The VSS wire sends a series of pulses, anywhere from 800 to just over 1,000 per mile, and sends these pulses only when the car is in motion. If the VSS wire is not hooked up, then the unit will not realize that the car is moving at all, and will be unable to track position.

try this forum: http://www.mp3car.com/vbulletin/

jimmyblue

iTrader: (11)

Start with disconnecting the VSS tap and see if the car functions
return to normal. If so then it's either a loading problem (add a
resistor between vehicle VSS and nav unit, try a blocking capacitor
or whatever you can determine based on the nav unit info at hand,
what its input might like) or an actual defect or a miswire.

Separate possibilities from the herd one by one starting with the
weakest.