VSS update "Help"

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Jul 10, 2007 | 05:13 AM

bmcm94

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VSS update "Help"

I have been fighting a problem with my 94, f350, 7.3, e4od, 240k miles. It’s very intermittent problem it throws a code 29 weak/ intermittent vss signal and puts the trans in fault mode. It only seems to happen at slow speed when I’m on and off the throttle in traffic or around town it hasn’t happened at highway speed. The speedometer doesn’t really bounce as bad as I have heard others do only very slight maybe a mph or two at the most. I seem to have a good sign voltage from the vss (the vss is new) and I have completely replace all the wiring from the sensor to the firewall, I have good continuity from the fire wall to the psom (dash cluster) and back out to the pcm (the pcm is about a year old). Do you have any suggestions is this similar to any problems you have heard of could it be caused by the PSOM? [/font]

Jul 10, 2007 | 06:41 AM

Cuda_jim

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From: MICHIGAN

Have you checked the exciter ring in the rear gear for damage or the clearance between the VSS and the exciter. I wonder if dirty fluid would cause this. There is a certain amount of metal particles in the fluid that may interfer with the signal at low speed. Just thinking out loud. PSOM could be it too, have you actually monitored the signal while driving it? There is a RABS data link connector under the hood at the LH rear of engine compartment, on a bracket. It's a 3 hole connector with only 2 wires coming from it. R/PK and LG/BK. The Cruise control is inline with the signal and may be something to look into. Also the RABS module can be the culprit It's on the RH side of the dash by the passengers feet. And then there is the hydraulic side of this too. It takes some very specialized tools and diagnostic equipment to figure out both the electrical and hydraulics. Some brake shops have them, most don't know how to use them.

Jul 10, 2007 | 06:56 AM

bmcm94

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I have checked the ring and changed the fluid there wasen't anything on the vss sensor to speek of. I put probes in the back of the connecctor at the fire wall and with the truck jacked up spun the wheels to check the voltage. Any info on how to check out the rabs module? I don't ever use the cruise control can this be eliminated without causing any ptoblems?

Jul 10, 2007 | 12:41 PM

Cuda_jim

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From: MICHIGAN

I just looked in the repair manual and the RABS module will set a code if it's bad. So maybe that's not your problem.

When you check the RABS output did you get more than 650mV AC? IF not the sensor is bad.

MEASURE RABS SENSOR OUTPUT
Put vehicle on hoist and raise so that the rear wheels can rotate freely.
Verify the vehicle is in 4x2 mode and hubs are unlocked.
Set an AC voltmeter on the 2000mV scale.
Remove the cap from the RABS sensor test connector and connect the AC voltmeter across the connector leads.
Start the engine and turn the rear wheels at 8 km/h (5 mph).
Measure the voltage output of the RABS sensor.
Is 650mV or more registered?

Aug 4, 2007 | 05:23 PM

DYDF250

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Well guys what is the outcome from this problem. I have the same problem, bmcm94,
you have discribed the same situation I am in with my truck 95 F250.

Mark

Aug 6, 2007 | 05:05 AM

bmcm94

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I have changed out the psom a couple of weeks ago but have only put on 1500 miles but I have not had the problem again but my problem was very intermitent and may still be to soon to tell.