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VSS

K

ktwalker01

NAXJA Forum User
Location
Jackson, WY
99 4.0l np231 ax15

Okay so my speedometer went out 2 weeks ago. I went on the jeep verified the wiring and the sensor was getting 5 volts at the connector, the gear is in great shape, along with the gear on the output shaft in the transfer case ( it has no play). SO i ruled the sensor went bad only because for the past few months sometimes the speedo would quit and come right back. I replaced the sensor and it still is doing nothing... What gives? Any one fight something similar like this on a 97+

Like I said the wiring is good at the connector.

I'm waiting for my drill to charge to see if that will give me any kind of a reading by spinning the sensor directly and looking at the speedo.
 
drill test was no good.

Also I am getting 5v from both the orange white cable and orange purple cable..

I really hope this isnt going to be a computer...
 
is the odometer counting, or no? it sounds like the speedo died. or there's an issue with the electrical connection at the back of the cluster, kinda common on the late models.
 
Physically inspect the wires and wire plugs more closely for corrosion, damaged or misaligned wire pins, and chafed or melted wires. Don't forget the plug near the dipstick.
 
That should be correct. Like a lot of the other sensors, it uses a 5v reference. Sounds like either the connection at the vss is bad, you're losing the signal upstream toward/at the speedo/cluster, or the gauge itself died.

ktwalker01 said:
Well my concern is Im getting 5 volts on pin 1 and 3 on the connector and if that's normal..
Click to expand...
 
I forgot to add this in my original post but i am throwing a cell from before with the old sensor and now with the new one it popped up again p0500 i reset and cleared it to make other go away. It went away and came back after a reset with both the old and new sensor. I traced the wired and connectors all is good no burnt or frayed. I removed and reseated the cluster. Also unplugged the computer and and rechecked all connections as well.

Im figuring its the computer i don't know what else is killing me here I've thrown a ton of money at this rig in the past few months and Im trying to not throw more. Ugh i love this xj to much.

Chime in with ideas...
 
Is the VSS properly clocked in the t-case?
 
Well IIRC on the 99's the speed is bussed out to the cluster through the ECU, so what I would do is see if the ECU is seeing VSS. I would either see if you can barrow a DRBIII or find a cheap obd2 to laptop adapter. That should help you figure out if it's the something going to the ECU or something going to the cluster.

Also you can have the gauge cluster do a sweep test, hold down the odo reset and turn the key on and see if the speedo sweeps.
 
tj'sxj said:
how that work, thought ya just plugged her in?? not to poach!
Click to expand...

The retaining clip is C-shaped. And the VSS has notches with numbers next to them. The tang on the outer end of the clip has to be in the notch that corresponds to the number of teeth on the speedo gear.

For example, if you have a 39-tooth speedo gear, the clip has to be in the notch that says "36-40". (I forget the actual numbers on the VSS.)

If the clip is not in the correct notch, the speedo will work erratically, or not at all. So I'm thinking that the OP may have had a bad VSS and did not properly clock the new one.
 
I put it in the same way the old one came out (formerly working one). Ill check this issue when it stops pouring out.

Yes I did a cluster sweep all works well.

The thing its been doing is it wont read anything and then out of no where for 1 second im doing about 110 mph and then nothing.
 
ktwalker01 said:
..sometimes the speedo would quit and come right back.......out of no where for 1 second im doing about 110 mph and then nothing.
Click to expand...

To me, this points to a wiring/electrical issue. Water/dampness inside the wire plugs can short out the signal and cause erratic readings, I have seen it happen. Failure of the ECU or the cluster itself is rather unlikely.

Clean and dry all the wire plugs with electrical contact cleaner and re-assemble them them a coating of dielectric grease.
 
ktwalker01 said:
Well my concern is Im getting 5 volts on pin 1 and 3 on the connector and if that's normal..
Click to expand...

I wouldn't think you would have 5 VDC on pin 3 of the connector. That's the VSS signal from the VSS to the PCU. Looks like there's a short from pin 1 wire (5 VDC supply from the PCU), or from another source.

You can disconnect connector C2 (White) from the PCU and see if that 5 VDC at pin 3 goes away. If it does the short may be in the PCU. If it's still there, the short is between PCU C2 and the VSS connector.
 
Sidewinder CC said:
I wouldn't think you would have 5 VDC on pin 3 of the connector. That's the VSS signal from the VSS to the PCU. Looks like there's a short from pin 1 wire (5 VDC supply from the PCU), or from another source.

You can disconnect connector C2 (White) from the PCU and see if that 5 VDC at pin 3 goes away. If it does the short may be in the PCU. If it's still there, the short is between PCU C2 and the VSS connector.
Click to expand...

Sorry, my wife was yelling at me so I sent the reply before I was finished. LOL

With the PCU C2 connector disconnected use an Ohmmeter to read between pins 1 and 3 of the VSS connecor to see if these wires are shorted.
 
Sidewinder CC said:
I wouldn't think you would have 5 VDC on pin 3 of the connector. That's the VSS signal from the VSS to the PCU. Looks like there's a short from pin 1 wire (5 VDC supply from the PCU), or from another source.
Click to expand...

Thats what I was thinking to. I was always under the impression pin 1 5v power source powers the sensor, and then pin 2 ground. and pin three would be output voltage based on speed.

with the sensor disconnected and the key in the on position when I checked the
pigtail off the wiring harness I was getting 5v on both pin 1 and 3.

Excellent advice I will give this a shot and report back.
 
Last edited:
okay so i finally had time to mess around with this. Everything basically led me back to the computer with the connector removed from the computer i had infinite resistance, but with it connected to the computer i had zero. With me testing the pins directly at the computer i got zero resistance. The pins i was testing were input and output.

Im convinced its the computer at this point unless this is what its supposed to be. There is a company up in davie Fl a few miles north of me that has a good ebay store and good review quoted me 160$ for it. Jeep doesn't even have the ecu for a 99 xj 4.0l manual discontinued womp womp

Let me know if im making the right choice.
 
ktwalker01 said:
okay so i finally had time to mess around with this. Everything basically led me back to the computer with the connector removed from the computer i had infinite resistance, but with it connected to the computer i had zero. With me testing the pins directly at the computer i got zero resistance. The pins i was testing were input and output.

Im convinced its the computer at this point unless this is what its supposed to be. There is a company up in davie Fl a few miles north of me that has a good ebay store and good review quoted me 160$ for it. Jeep doesn't even have the ecu for a 99 xj 4.0l manual discontinued womp womp

Let me know if im making the right choice.
Click to expand...

with the connector removed from the computer i had infinite resistance,

Isthis reading between pins 1 and 3 at the VSS connector? If so, this is good.

but with it connected to the computer i had zero.

Isthis reading between pins 1 and 3 at the VSS harness connector? If so, it may be a short inside of the PCU. Did you examine the connector on the PCU closely for corrosion around pins B32 and B27?

Try a little shock therapy (using a small hammer - gently now) on the PCU above connector C2 when it's connected to the PCU and while reading between pins 1 and 3 of the VSS connector with your Ohmmeter. See if anything changes.

I have no idea what the inside of the PCU looks like but my guess is that there are wires running from its connector to a printed circuit board. Any short would probably be in that wiring, not the PCB.

There are several shops that repair PCU's. You may want to contact one and see if you can talk to someone about this.
 
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