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Chris (aka- Moose)
Chris (aka- Moose), Technician
Category: Ford
Satisfied Customers: 48688
Experience:  16 years experience
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I have a no speedo situation no codes abs light is on VSS

Customer Question

hello pearl i have a no speedo situation no codes abs light is on VSS wires are good from sensor to pin 33 on ABS module as well as from sensor to ECM ? replaced VSS got a P720 eraced codes test drove nothing no codes and VSS is reading erraticly
JA: Have you checked all the sensors?
Customer: ohm'd sensors at VSS and OSSS and both are within spec
JA: What is the model/year of your Ford?
Customer: Early 1999 F250 2WD NVK3 ECM
JA: Are you fixing your F250 yourself? What have you tried so far?
Customer: auto
JA: Anything else you want the mechanic to know before I connect you?
Customer: tested wiring harness and it appears to be ok
Submitted: 11 months ago.
Category: Ford
Expert:  Chris (aka- Moose) replied 11 months ago.

Welcome, I'm Chris (aka Moose), my normal schedule online is around lunch and after dinner past midnight.

Are you getting the erratic speed signal in the ABS and PCM when scanned?

Is the transmission shifting poorly?

Customer: replied 11 months ago.
Erratic reading on IDS ABS light on constantly but no codes trans shifting seems normal
Customer: replied 11 months ago.
VSS reads seemingly normal to about 30-40 mph then goes straight to 116
Expert:  Chris (aka- Moose) replied 11 months ago.

If you access the PIDS in the ABS and monitor the rear wheel speed sensor on a graph does it to show this inconsistency?

Customer: replied 11 months ago.
Have not graphed it yet
Expert:  Chris (aka- Moose) replied 11 months ago.

Can you try that and let me know the results?

Customer: replied 11 months ago.
I monitored the vehicle speed sensor through the transmission module on the IDS the graph followed the numbers that were being displayed in that erratic fashion
Expert:  Chris (aka- Moose) replied 11 months ago.

This vehicle does not have a transmission control module. The PCM controls the 4R100/E4OD transmission.

Is this a light or super duty F250?

What liter engine?

Customer: replied 11 months ago.
Early 1999 F250 7.3 Auto
Customer: replied 11 months ago.
I understand that the tcmpcm is the same thing all encompassed in the ECU correct
Expert:  Chris (aka- Moose) replied 11 months ago.

They are all called the PCM. Ford rarely calls its computer modules ECM or ECU like other make vehicles.

Here is a diagram of this circuit. https://dl.dropboxusercontent.com/u/90220402/gybk.pdf

So far the ABS module looks to be to blame here. We need to watch its reading from the rear sensor and its VSS signal it is making when only monitoring the ABS. If the signal is messed up there, then it is the ABS module sending out a bad VSS signal.

Prior to completing the mandatory rating at the top of your screen. Let me know if I have not yet provided you with ~5 STAR EXCELLENT~service. Reply and let me know in more detail what you need to be pleased with my help.

Thanks Chris

Customer: replied 11 months ago.
the ABS module reads converts then sends signal to the PCM and cluster?
Expert:  Chris (aka- Moose) replied 11 months ago.

That is correct the ABS makes the VSS signal and sends it out to everything.

Customer: replied 11 months ago.
if the ABS module is sending a false signal it can cause the p0720 and the p0500 and the constant ABS light even with no codes
Expert:  Chris (aka- Moose) replied 11 months ago.

When the PCM does not get a VSS signal it tries to get a signal from the OSS. When it notices VSS and OSS differing it stores both codes.

Expert:  Chris (aka- Moose) replied 11 months ago.

Hello again Chris here,

  • Sorry you were not pleased with my help.
  • What would you like to do regarding your question now.
  • This post is coming up on the 7 day mark where it times out. When a post times out, that means it's no longer on my active list (you reply and I may never know it.)

Thanks Chris

Customer: replied 11 months ago.
Hey Chris sorry for not responding yet I sent the VA BS module out to have it repaired got it back and I still have an ABS light no speedo the output shaft speed sensor picks up the reading on the IDS but nothing from the vehicle speed sensor I check the wires from the speed sensor to the ABS module they are good I check the ABS module the VSS power line to the PCM and that is also good just curious as to what your thoughts might B I tried another PCM and that also did not fix the problem any idea on how to go or where to go from here could it possibly be the cluster I feel as if I have checked all wiring and everything comes back good
Expert:  Chris (aka- Moose) replied 11 months ago.

What codes are stored in the ABS?

Is the ABS showing an accurate reading from the rear axle speed sensor?

I believe your ABS module is bad.

Customer: replied 11 months ago.
I replaced the ABS module already this truck is an early 1999 2wd
Expert:  Chris (aka- Moose) replied 11 months ago.

2 hours ago you said you sent the ABS module off to get repaired.

Was it repaired or replaced?

What codes are stored in the ABS?

Is the ABS showing an accurate reading from the rear axle speed sensor?

Customer: replied 11 months ago.
Oh that's correct my fault it was repaired the ids has no reading on the rear speed sensor no codes
Expert:  Chris (aka- Moose) replied 11 months ago.

Your ABS module is bad or is not even powering up since your IDS can not get codes from it and the warning light is on.

Customer: replied 11 months ago.
Ok then I'm guessing the "repair" was unsuccessful problem is I cannot get one from Ford because they're obsolete.
Expert:  Chris (aka- Moose) replied 11 months ago.

I suspect the rebuild was not successful.

Customer: replied 11 months ago.
What would cause the module to not power up? If it's not the module itself?
Customer: replied 11 months ago.
Thieves I tell ya!
Expert:  Chris (aka- Moose) replied 11 months ago.

Blown fuse, damaged wiring or connector, bad grounds. All of these can cause an ABS module to not power up.