Speedometer not working
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Speedometer not working
I have a 98 expy, 4.6L, 2wd that the speedometer is not working in. i have checked for 5 volts on the VSS plug and got zero volts. Guess it could be the PCM. Does anyone have a schematic of the PCM or a good wiring diagram to trace the wires back to the PCM? not really wanting to shell out 300+ for a new PCM. Does anyone have any other suggestions for this problem.
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another question about the VSS. it looks like the one i have in my 94 explorer, are they the same? The explorer has what i would assume is a speedometer cable that plugs into the VSS and the Expy only has an electrical connector, no other cables.
just curious.
just curious.
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From: Georgia
rrumba- Here is a link for the diagram. I could not import it into this reply, so I uploaded it to a sharing site. I hope it gives you enough detail. The file is in Word format.
Other than having the diagram, I don't know much about the VSS.
http://www.bestsharing.com/files/1qZdDG367938/VSS%20diagram.doc.html
Other than having the diagram, I don't know much about the VSS.
http://www.bestsharing.com/files/1qZdDG367938/VSS%20diagram.doc.html
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I have replaced the VSS, I have tried a new Reman PCM and still have the same problem. The odometer works fine, the speedometer does not, it does not shift correctly when you first step on the gas, it's like you have to wait for about 30-45 sec for it to engage and does some of the same when at higher speeds.
Can anyone suggest anything else?
Can anyone suggest anything else?
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ok, i checked some other items such as continuity from the connector at the VSS to the PCM, pin 58, and to the cruise control amp. all show a short as they should. still no 5 volts from the PCM with the key on, not running. In the process i also checked the GEM, pulled it out, and now the theft light is flashing. i believe i have th PATS 1 as the key has an oblong hole that is offset. Problem is there is only one key. after reading some other posts i have 2 keys on the way. with all that i have 2 questions,
1. is the PCM relay before or after the PCM, does it have something to do with helping generate the 5 volts?
2. can a locksmith program the one key that i have that no longer works since i disconnected the battery and fuse panel and seem to have lost the programming?
1. is the PCM relay before or after the PCM, does it have something to do with helping generate the 5 volts?
2. can a locksmith program the one key that i have that no longer works since i disconnected the battery and fuse panel and seem to have lost the programming?
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ok, so i got the key problem taken care of, it was a bad diode in the engine compartment power distribution box. now back to the pcm and missing 5 volts
does anyone have a schematic for the PCM itself or suggest other ways to ensure the PCM is not the cause or is?
does anyone have a schematic for the PCM itself or suggest other ways to ensure the PCM is not the cause or is?
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Logistics Pro
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From: Central NYS
Originally Posted by rrumba
I have a 98 expy, 4.6L, 2wd that the speedometer is not working in. i have checked for 5 volts on the VSS plug and got zero volts.
The VSS is a small gear-driven permanent magnet signal generator. It generates an AC signal whose frequency is proportional to vehicle speed.
This signal is available to the PCM on pin 58. The PCM uses this frequency to determine ignition timing, fuel injector on time, and to determine when to lock and unlock the torque converter clutch.
This signal is also used by the GEM module to control the automatic door locks and for the Programmable Ride Control, as well as input to the Instrument Cluster for speedometer control.
Additionally, this signal is used by the Speed Control Servo/Amplifier Assembly for Cruise Control. I believe its also used by the EVO (Electronic Variable Orifice) Variable Assist Steering module.
What leads you to suspect a problem with the VSS?
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hi going from past similar experiences that the transmission would not be shifting if the computor wasnt recieving a signal. the speedometer can be in a no working condition and the computor still recieve the appropiate signal. so with that said I believe the problem lies in the speedometer head itself versus the computor or the VSS. a scanner capable of giving the user the option of reading data stream would quickly give the answer. is the head analog or digital? have you driven the vehicle since replacing the diode?
Jack
Jack
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Originally Posted by pdqford
I'm not sure I understand why you are looking for 5-volts on the VSS wire.
The VSS is a small gear-driven permanent magnet signal generator. It generates an AC signal whose frequency is proportional to vehicle speed.
This signal is available to the PCM on pin 58. The PCM uses this frequency to determine ignition timing, fuel injector on time, and to determine when to lock and unlock the torque converter clutch.
This signal is also used by the GEM module to control the automatic door locks and for the Programmable Ride Control, as well as input to the Instrument Cluster for speedometer control.
Additionally, this signal is used by the Speed Control Servo/Amplifier Assembly for Cruise Control. I believe its also used by the EVO (Electronic Variable Orifice) Variable Assist Steering module.
What leads you to suspect a problem with the VSS?
The VSS is a small gear-driven permanent magnet signal generator. It generates an AC signal whose frequency is proportional to vehicle speed.
This signal is available to the PCM on pin 58. The PCM uses this frequency to determine ignition timing, fuel injector on time, and to determine when to lock and unlock the torque converter clutch.
This signal is also used by the GEM module to control the automatic door locks and for the Programmable Ride Control, as well as input to the Instrument Cluster for speedometer control.
Additionally, this signal is used by the Speed Control Servo/Amplifier Assembly for Cruise Control. I believe its also used by the EVO (Electronic Variable Orifice) Variable Assist Steering module.
What leads you to suspect a problem with the VSS?
The haynes stated that there should be 5 volts on the VSS gray/blk wire, understanding electronics, this should be the voltage needed in order to create the ac refrence sine wave needed for the PCM to adjust accordingly based on the speed. If the 5 volts is not present the manual suggests that it is the PCM. If the 5 volts does not come from the PCM then it comes from somewhere else. I am trying right to track down the source of the 5 volts. Granted i could be chasing my tail right now going off of the haynes manual.
I do not suspect the VSS as the problem, but whatever is supplying the reference voltage needed to create the ac sine wave. The haynes manual does not give a good wiring diagram or even show a PCM relay.
Any suggestions as to where else to look to fix the problem?
thanks for the reply
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Originally Posted by outsdr2
hi going from past similar experiences that the transmission would not be shifting if the computor wasnt recieving a signal. the speedometer can be in a no working condition and the computor still recieve the appropiate signal. so with that said I believe the problem lies in the speedometer head itself versus the computor or the VSS. a scanner capable of giving the user the option of reading data stream would quickly give the answer. is the head analog or digital? have you driven the vehicle since replacing the diode?
Jack
Jack
problem. The head is analog, the odometer and all other intrumentation works except the speedometer. Guess i will look at a trusted (if able to find one) shop to take it to and see what they can suggest.
if you can think of other suggestions that would be great. thanks for the reply.
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From: Central NYS
Originally Posted by rrumba
I do not suspect the VSS as the problem, but whatever is supplying the reference voltage needed to create the ac sine wave.thanks for the reply
If the auto door locks lock when you start moving, or if your cruise control can hold a steady speed, the VSS is okay.
If the speedometer is not working, but the odometer is working, the instrument cluster has to go in for repairs.
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I'm glad you guys brouth this up as I too though the only voltage on the VSS lines were the induced signal by the spinning magnet.
I will see one of my Ford tech friends sometime this week and will ask him if there should be voltage present or not.
I will see one of my Ford tech friends sometime this week and will ask him if there should be voltage present or not.
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Originally Posted by pdqford
AFAIK, a reference voltage is not need to create the AC signal - it is generated by the permanent magnet in the VSS.
If the auto door locks lock when you start moving, or if your cruise control can hold a steady speed, the VSS is okay.
If the speedometer is not working, but the odometer is working, the instrument cluster has to go in for repairs.
If the auto door locks lock when you start moving, or if your cruise control can hold a steady speed, the VSS is okay.
If the speedometer is not working, but the odometer is working, the instrument cluster has to go in for repairs.
Just tested out the cruise control, and yes it does hold the speed, and the auot door locks work when you drive away as they should. Following out the limited diagram that i do have then that would make sense that the ref voltage is present or the speed control servo amp would not work which in turn means no cruise control.
Then that would bring up another question about the GEM. is the path through the GEM or is it just a tie point? I looked at the 3 connectors that plug into the side of the GEM and could not find the gra/blk wire on the pins that they show them on, again i could be looking at the wrong location based on the one diagram that i do have.
I will look at the cluster and see if there is something/someone that can do some repairs or find a shop that could possibly isolate it for me since i do not have a scanner.
thanks for the info and the assistance.
Originally Posted by fte herman
I'm glad you guys brouth this up as I too though the only voltage on the VSS lines were the induced signal by the spinning magnet.
I will see one of my Ford tech friends sometime this week and will ask him if there should be voltage present or not.
I will see one of my Ford tech friends sometime this week and will ask him if there should be voltage present or not.
If you find out please let us know, i would be interested it that.
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From: Central NYS
Originally Posted by rrumba
Then that would bring up another question about the GEM. is the path through the GEM or is it just a tie point? I looked at the 3 connectors that plug into the side of the GEM and could not find the gra/blk wire on the pins that they show them on,
Again, this signal isn't a 5-volt reference signal. The modules look at the frequency of this signal to determine the vehicle speed. When a predetermined frequency is reached, the GEM locks the doors. When the correct frequency is reached, the PCM considers locking the torque converter, depending on TPS, engine load, coolant temp, etc., etc.