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Vehicle Speed Sensor Error

skiinxs

New CEG'er
Joined
Nov 1, 2006
Messages
5
I have a 98 Mystique auto w/2.5 Liter (daughters car). I have been battling a VSS error for several months. (I have researched all of the related posts on this forum). The problem started manifesting itself with an occasional lurch on the highway. My daughter told me this several times over several months, but when I drove the car it never did it. The CEL light then came on, when I checked it there was a vehicle speed sensor error code. I had the VSS replaced and the code came back a month later. I then started paying attention to the indicated vehicle speed coming out of the computer (I use Autotap software on my laptop) and noticed that the speed reading was sometimes wrong. The speed would indicate 0 to 60 mph when the car was running in park, and vary all over the board when driving. The actual vehicle speedometer ALWAYS reads correctly, sometimes not agreeing with the indicated speed from the ecm. I once again replaced the VSS. This once again did not fix the problem. I checked all of the grounds and battery cables. Indicated voltage on the ecm and my voltmeter on the battery agree and are stable around 13.8 when the vehicle is running, so I think I have ruled out that issue. My next thought was either a bad connection or bad wiring between the sensor and the ecm. (When I looked into the wiring on this car I was shocked to see very deteriorated insulation on many of the wires). Since the ecm seems to see a signal when the speedo doesn't, I suspected some sort of interference getting into the wire from the sensor to the ecm, so I cut the wire at the sensor, found the correct wire at the ecm connecter, and spliced a coax in between to replace the stock wiring, grounding the shield at both ends. (I always solder and heat shrink all connections) Other than the speedo not working, nothing changed. That should have ruled out wiring. Apparently the speedo splices off in the loom in the piece I bypassed. I hooked the factory wire back up at the ecm end and the speedo started working again. I then cut the wire again at the ecm so there was absolutely no feed going in and of course the speedo stopped working again and the computer no longer read vehicle speed, but the random output of 0 to 60 mph when in park persists, even with no wiring hooked up to the input to the ecm. My last guess is that the ecm itself has a problem in the circuit that converts the pulses from the VSS to whatever signal it reads, maybe an analog to digital converter of some sort. Unless someone on this forum has another idea, I am going to try to replace the ecm. Once again, the vehicle speedo has always read correctly, never jumping around as the speed indicated as read by Autotap from the ecm. It does appear to have the problem mainly when cold. Obviously the transmission shifts very poorly while the ecm indicates the incorrect speed and shifts properly when the ecm indicated speed agrees with the speedo. Did I miss anything? Any other ideas?
Thanks,
Dave
 
Welcome :) . If your CEL code is P0500, yes, it is VSS or VSS related issue.

P0500 is indicative of either one or combination of below faults.

* VSS signal circuit (hertz) is open or shorted to ground.
* VSS is damaged or failed.
* VSS power signal (VPWR) circuit is open.
* PCM is damaged

I suggest you check all the wiring before investing in a new PCM.

Edit. http://www.contour.org/FAQ/recall/99M03/Recall-ONP%2099M03_files/r99m03r.htm

VSS wiring is No. 21 in ATX 2.5 schematic.

VSS has 3 wires. Green/Red (to MAF sensor), White/Blue (signal to PCM) and Black/Orange (to Power Steering??) . Check with your DVOM and post the results.
 
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re: VSS error

re: VSS error

I appreciate the link to the wiring bulletin, but the car is a 98 and has 122,000 miles, so it is beyond their extended coverage period. It is odd that they only extended the coverage throught 97's as though they thought they had it corrected and my 98 has the exact same issue. Since I have run a direct signal wire to the ecm to bypass the wiring harness I don't think it is the wiring. I am still leaning towards the PCM. Do you know how the VSS signal (hertz) is converted inside the PCM? Analog to digital converter of some sort? My guess is that is the problem. I will post the results after I replace the ECM.
Thanks,
Dave
 
I appreciate the link to the wiring bulletin, but the car is a 98 and has 122,000 miles, so it is beyond their extended coverage period. ....Do you know how the VSS signal (hertz) is converted inside the PCM? Analog to digital converter of some sort? My guess is that is the problem. I will post the results after I replace the ECM.
Thanks,
Dave

The wiring harness link was posted for you to probe the wires to determine if those were the problems.
 
Re: VSS error

Re: VSS error

Thanks! I hadn't scrolled down far enough to see all of the detail on the link. The actual error code was P1500, which I believe is "Intermittent VSS signal.
Dave
 
I think I have some sort of VSS problem but my symptoms are different than any of the other ones I have read. I have a 99 se with MTX, When I get up to about 40 MPH the speedo just sticks there. If I go faster it does not move, and does not come back down until I brake aggresively. I think I should just change the VSS right?
 
I think I have some sort of VSS problem but my symptoms are different than any of the other ones I have read. I have a 99 se with MTX, When I get up to about 40 MPH the speedo just sticks there. If I go faster it does not move, and does not come back down until I brake aggresively. I think I should just change the VSS right?

Did you install an aftermarket instrument panel? It sounds like the needle is stuck. You may want to check that first.

Some info on taking the panel out.
http://www.contour.org/ceg-vb/showthread.php?t=202
 
I was thinking maybe that too.... I looked. there is plenty of room. After I wrote this and went back to my car for lunch, it worked perfectly the whole way. Weird... Intermitten speedometer stuck.
 
Re: VSS error

Re: VSS error

Well, I bought a new PCM and installed it but still have the same issue. :mad: P1500 intermittent VSS error. The only other thing that I can think of is to try a third Vehicle Speed Sensor. Since I did run a shielded coax between the vss and the PCM, I really don't think the problem is the connection between the VSS and PCM. (I soldered and heat shrinked the splices and grounded the shield at both ends.) One other idea is maybe there is some sort of intermittent connection on the other wires connected to the VSS. (It ws mentioned that "VSS has 3 wires. Green/Red (to MAF sensor), White/Blue (signal to PCM) and Black/Orange (to Power Steering??)") Does anyone know if the MAF sensor or Power Steering wires are supplying voltage to the vss to create the signal or are they simply another signal that the vss sends? When I monitor the sensor with my Autotap and laptop, I did get a value of "8" on the "Maximum Intermittent VSS Fault Value" while the care was on the highway. A few minutes later the P1500 code was set. What am I missing????
 
VSS Error Update

VSS Error Update

Well, I got a little time to work on it again last night. I purchased another VSS from Ford, pulled the old one out, tested the wiring at the connector while it was apart (removed the coax I had previously tapped in to the wiring on the VSS itself). Ground wire good, no intermittent issues with the car running or off, 12v wire good, no intermittent issues with the car running or off, VSS signal wire around 100 ohms resistance both running or off. PCM indicated through laptop via Autotap stable zero speed with car running or not running (with key on) before plugging in new VSS. After pluggin in VSS speed indicated at PCM varying all over the board, speedometer stable at zero. Cut VSS signal wire at PCM, indicated speed on laptop stable at zero. Voltage at VSS side of cut wire stable at 13.6v. reconnected wire, speed all over the board, voltage still stable ate 13.6 and car speedo stable at zero. Tested old VSS by hooking up 12v to power wire, ground wire to ground, tested voltage at signal wire. Voltage flipped from zero to 12v as shaft turned. Everything checks out as I would expect but the #@!#* speed reading still varies. I now have to go back and suspect a dirty signal in the VSS wire into the PCM, possibly RF interference. I think I am going to go to Radio Shack and buy one or more RF filters. I looked at their web site, they have an inline filter that I am going to put on the signal wire immediatly before it goes into the PCM. They also have some pass through coils that I am going to put around the loom close to the PCM and around the alternator wire at the alternator. I'll let you know if any of that works. Anyone want to buy a "lovely" Mercury Mistake??:crazy:
Dave
 
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