smarrs

Hi all, I've got a 2000 XJ, auto, 4wd. My speedo quit working yesterday. Through searching I found a few things to try.


I cleaned the ground points on the side of the block and fenderwell, pulled the VSS and inspected the gear (it looks like new), the contacts look nice and clean. I also pulled the cluster and tightened the screws to the board, and performed the cluster test (tested fine).


Now I am trying to figure out how to test the wires. I checked pin one and am getting 5.13v. My first question is about testing pin 2. I'm supposed to get a reading of 0 (or close to) ohms, if I understand correctly. If the ignition is on I'm reading around 16 ohms, with it off it varies from 0 to -.2 ohms. Am I supposed to test pin 2 with the ignition in the on position or in the off position? My second question is about pin 3. Is there any sort of test that I can/should do on it?


I am just trying to rule everything out before I go and buy a new VSS. I've read numerous threads where people have replaced it and it was not the issue. If there are any other suggestions of what to try I would appreciate it. Thanks in advance!

CCKen

You've figured out that you have the 5 volts +/- .5 volts available as the supply voltage (Violet/Orange tracer wire), but you don't need to be checking resistance (Ohms) at this point. In fact, you shouldn't be using the Ohms scale on your meter with system voltage on line - it may hurt that function of your meter.

At pin 2, Brown/Yellow tracer wire, you should see between .016 and .020 volts with the ignition switch to ON (engine not running) and zero volts with the switch OFF/LOCK. Meter + probe to pin cavity 2 and meter - probe to the transfer case as the meter ground.

Pin 2 is the Sensor Ground. It splices into the sensor ground network, which includes just about every sensor in the Jeep, so that .016 volts should be seen at any sensor, like the TPS, Brown/Yellow tracer wire.

Pin 3 is the Sensor Signal wire. You won't see any voltage readings here with the VSS not hooked up and turning. The only way to check this wire is to unhook the PCM connector C2 and read the resistance of the wire from PCM C2, pincav 27 to VSS pin cv 3. Max 5 Ohms.

If these readings are okay...

Examine as much of the VSS wire harness as you can get at for chafing, etc. Examine the VSS connector for pin cavity damage (corrosion, enlaged cavs, cavs pushed back inside the connector) if everything is okay, shotgun a new VSS.

Are all other instruments functioning okay?

smarrs

CCKen, thanks for the response. I just went out and probed 2 (with meter set at 20) and got nothing. So, does this mean that that wire is shorted out somewhere between the sensor and the PCM connector? I am pretty much a novice when it comes to the electrical stuff. Is the C2 connector the large grey one close to the dipstick tube for the tranny? It seems my issue would be with this wire, but just for my own understanding regarding pin 3 are you saying to check resistance from pin cavity 27 in the c2 harness to the cavity for pin 3 by the tranny?

smarrs

Forgot, yes all other gauges are working, but the odometer of course is not.

CCKen

When you checked pin cav 2 did you have the ignition switch turned to ON/RUN (setting just before cranking the engine?

If so, and you got zero volts there's no short. It would mean there's an open in that circuit.

Don't worry about checking the pin cav 3 wire to the PM until it is resolved that you do have connection to the ground circuit (pin cav 2).

smarrs

Yes, the ignition was in the on/run position (engine not running). How do I proceed from here?

CCKen

To double cheack that sensor ground circuit, go to the TPS and repeat the voltage reading procedure there. Again, Brown/Yellow tracer wire. To check even futher do it on the MAP sensor.

All sensor ground circuit wires are Brown with a Yellow tracer.

smarrs

OK, just got home and tested the MAP and the TPS, both read .009v. The speedometer started working on the way home. It operated normally for about half the drive and then it started jumping around. I checked the VSS as well thinking that since it was working intermittently that I would get something, but it is still reading 0.

CCKen

You're in the ballpark with the .009 Volts. Check battery voltage.

Sounds like you have an intermittant open in that Sensor Ground wire. Start wiggling wire harnesses and checking voltage - on and on until the voltage reappears. It would be adviseable to have an assistant wiggle wires or watch the voltmeter.

You'll be wiggling harnesses all the way from the VSS to the PCM - no shortcuts.

If, per chance, the .009 volts appears when wiggling, that's the open spot.

Let us know what you find.

smarrs

After testing the voltage of the MAP, TPS, and VSS I pulled the wires out of the loom all the way into the engine bay, looking for any suspect looking areas. I didn't see any and now it is working constantly. I must have moved something just right. I'm sure it will be back but is working for now. I'm going up to Oklahoma to go camping tomorrow so we'll see how it does. When I have an afternoon and somebody to help guess I'll have one of us monitor the output on pin 2 and the other wiggle wires/connectors.

Thanks CCKen for you're input!! I'll post here if I track it down.