VSS Testing
#31
11-18-2015, 04:51 PM
Hotshot
From this thread: https://www.ford-trucks.com/forums/1...t-come-on.html
#36
04-30-2017, 11:49 AM
1997 f250 7.3
Ok 1995.
Put jack stands under the rear axle.
There should not be a plug under the dash for this system other than the plug for the RABS module.
The plug should be at the drivers hood henge just aft of the EEC Self-Test plug.
Put a A/C volt meter on this plug, it only has two wires.
Run the truck up to 30 MPH.
Does the voltage increase smoothly and continuously from 0 to approximately 3.5 volts AC as vehicle speed increases from 0 to 48 km/h (0 to 30 mph) at the plug?
If not unplug the RABS module and see if you get it now.
If not unplug the PSOM also, do you get the VAC now?
If not change out the VSS sensor at the rear end.
If the wiring is OK and you still do not get the voltage reading then you may have a bad tone ring or bearings in the rear end.
Put jack stands under the rear axle.
There should not be a plug under the dash for this system other than the plug for the RABS module.
The plug should be at the drivers hood henge just aft of the EEC Self-Test plug.
Put a A/C volt meter on this plug, it only has two wires.
Run the truck up to 30 MPH.
Does the voltage increase smoothly and continuously from 0 to approximately 3.5 volts AC as vehicle speed increases from 0 to 48 km/h (0 to 30 mph) at the plug?
If not unplug the RABS module and see if you get it now.
If not unplug the PSOM also, do you get the VAC now?
If not change out the VSS sensor at the rear end.
If the wiring is OK and you still do not get the voltage reading then you may have a bad tone ring or bearings in the rear end.
subford - I have problem I have been chasing for a bit and would like you to weigh in my abs light comes on around 15 mph my spedo works great but It won't shift down at crusing speeds and no cruise kinda dumb founded tried to ground out wire under the passenger dash to see flash code got nothing. Tried some other stuff got nothing like replaced rear diff speed sensor. Plan on doing the procedure up above tomorrow when I see the truck. But if you have any input that would be great
#37
04-30-2017, 01:19 PM
If the speedometer works great then the VSS signal would be OK to the PSOM and abs system.
Sounds like maybe you have a problem with the abs system and you would then to see what codes the abs has to why it turned on the abs light.
I am not talking about the PCM codes as the abs codes are from the abs system. The PCM does not know the abs system even exist.
It also sounds like the "cruise" (the speed control system) and the shift down has a problem also, maybe a bad TPS. You need to see what codes you have stored in the PCM to track this down. The KOEO electrical test might tell you something but the stored codes is what you need to look at.
Sounds like maybe you have a problem with the abs system and you would then to see what codes the abs has to why it turned on the abs light.
I am not talking about the PCM codes as the abs codes are from the abs system. The PCM does not know the abs system even exist.
It also sounds like the "cruise" (the speed control system) and the shift down has a problem also, maybe a bad TPS. You need to see what codes you have stored in the PCM to track this down. The KOEO electrical test might tell you something but the stored codes is what you need to look at.
#38
04-30-2017, 04:55 PM
If the speedometer works great then the VSS signal would be OK to the PSOM and abs system.
Sounds like maybe you have a problem with the abs system and you would then to see what codes the abs has to why it turned on the abs light.
I am not talking about the PCM codes as the abs codes are from the abs system. The PCM does not know the abs system even exist.
It also sounds like the "cruise" (the speed control system) and the shift down has a problem also, maybe a bad TPS. You need to see what codes you have stored in the PCM to track this down. The KOEO electrical test might tell you something but the stored codes is what you need to look at.
Sounds like maybe you have a problem with the abs system and you would then to see what codes the abs has to why it turned on the abs light.
I am not talking about the PCM codes as the abs codes are from the abs system. The PCM does not know the abs system even exist.
It also sounds like the "cruise" (the speed control system) and the shift down has a problem also, maybe a bad TPS. You need to see what codes you have stored in the PCM to track this down. The KOEO electrical test might tell you something but the stored codes is what you need to look at.
#40
04-30-2017, 07:21 PM
I will go ahead and guess you have a 1997 F250. If so the following will apply.
CAUTION:
Care must be taken to connect only the black/orange stripe wire to ground. Connecting the red mating connector wire to ground will result in a blown fuse.
Diagnostic Trouble Codes, Retrieving
Verify the key is in the RUN position (engine does not need to be running). Next, locate the black RABS II diagnostic connector. The diagnostic connector has two mating halves (one of which has a black/orange wire connected to it). Disconnect the two halves.
Attach one end of a jumper wire to the black with orange stripe wire side of the diagnostic connector. Momentarily ground the other end of the jumper wire by connecting it to a good chassis ground for 1-2 seconds. Grounding this wire should start the yellow REAR ABS warning light flashing. If grounding this wire does not start the yellow REAR ABS warning light flashing, go to the «Symptom Chart».
The code consists of a number of short flashes and ends with a long flash. Count the short flashes and include the following long flash in the count to obtain the code number. For example, three short flashes followed by one long flash indicates diagnostic trouble Code 4. The code will continue to repeat itself until the key is turned off. It is recommended that the code be verified by reading it several times. This code will be used later for system service instructions. It should be written down for future use. Diagnostic trouble code 16 indicates that the anti-lock electronic control module detects normal system operation.
RABS diagnostic connector is located in the cab and clipped on the main instrument panel wiring harness about three inches below and to the right of the anti-lock electronic control module.
/
CAUTION:
Care must be taken to connect only the black/orange stripe wire to ground. Connecting the red mating connector wire to ground will result in a blown fuse.
Diagnostic Trouble Codes, Retrieving
Verify the key is in the RUN position (engine does not need to be running). Next, locate the black RABS II diagnostic connector. The diagnostic connector has two mating halves (one of which has a black/orange wire connected to it). Disconnect the two halves.
Attach one end of a jumper wire to the black with orange stripe wire side of the diagnostic connector. Momentarily ground the other end of the jumper wire by connecting it to a good chassis ground for 1-2 seconds. Grounding this wire should start the yellow REAR ABS warning light flashing. If grounding this wire does not start the yellow REAR ABS warning light flashing, go to the «Symptom Chart».
The code consists of a number of short flashes and ends with a long flash. Count the short flashes and include the following long flash in the count to obtain the code number. For example, three short flashes followed by one long flash indicates diagnostic trouble Code 4. The code will continue to repeat itself until the key is turned off. It is recommended that the code be verified by reading it several times. This code will be used later for system service instructions. It should be written down for future use. Diagnostic trouble code 16 indicates that the anti-lock electronic control module detects normal system operation.
RABS diagnostic connector is located in the cab and clipped on the main instrument panel wiring harness about three inches below and to the right of the anti-lock electronic control module.
/
#41
07-31-2017, 04:25 PM
I have the same problem with my 95 e350....replaced the vss twice....removed psom and had 9t checked ...put in a used one that speedometer place gave me to try while mine was being checked....same problem ..mine checked out ok so I put it back in... I currently have the abs unplugged....the thing is I get no Speedo for a few minutes of driving then it turns on and stays on until I turn the engine off....driving me crazy
#44
08-01-2017, 07:58 AM
Sounds like the gap is to large between the tone ring and the VSS.
Key OFF.
Remove the harness connector from the anti-lock electronic control module.
Raise the vehicle so that all the wheels (1007) are clear of the ground. If the vehicle is a 4x4, verify the transfer case is in the 4x2 mode.
Connect a Hand-Held Automotive Meter between harness connector Pin 10 (Circuit 523-R/PK) and Pin 3 (Circuit 519 -- LG/BK).
Set the meter to the frequency counter (Hz) setting.
Gradually spin up the rear wheels.
Does the frequency increase as the rear wheel speed increases?
Key OFF.
Remove the harness connector from the anti-lock electronic control module.
Raise the vehicle so that all the wheels (1007) are clear of the ground. If the vehicle is a 4x4, verify the transfer case is in the 4x2 mode.
Connect a Hand-Held Automotive Meter between harness connector Pin 10 (Circuit 523-R/PK) and Pin 3 (Circuit 519 -- LG/BK).
Set the meter to the frequency counter (Hz) setting.
Gradually spin up the rear wheels.
Does the frequency increase as the rear wheel speed increases?
#45
08-25-2017, 03:35 AM
Subford knows his stuff, and I can just about guarantee it's the psom, bec after a $2K trans rebuild from a shop that wasn't up to snuff, and rechecking by the original owner after he re-took ownership, while HE owed me nothing, he still spent the time to correctly diagnose the prob; psom. Found a used gauge cluster on eBay, swapped it, prob cured. From those few yrs, Ford ran the signal thru the psom ���� mother board, but when this prob reared its head, they went back to mboard ���� psom. Mileage change is the next hurdle; I gained ~100K �� Too complicated for my taste, but he knows his stuff.