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Buddy
Buddy, Technician
Category: Heavy Equipment
Satisfied Customers: 730
Experience:  20 years experience. Freightliner tech for last 14 years
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Looking for wiring diagram for a western star m the speed o

Customer Question

Looking for wiring diagram for a western star m the speed o meter does not work for about 30 miles then starts to work , replaced speed sensor and speedometer head
Submitted: 4 years ago.
Category: Heavy Equipment
Expert:  DR.Cummins replied 4 years ago.

Hello just wanted to let you know that the trans tone wheel that the speed sensor reads in important and always over looked. remove the sensor put a screw driver in the hole try to move the tone wheel if it moves at all you must replace it. Hope this helps

Customer: replied 4 years ago.
The ecm reads the speed but the speedometer is not right we feel it is either the connection out of the ecm or a connection along that wire harness somewhere we need a schematic that shows what pins are what out of the ecm
Expert:  Buddy replied 4 years ago.

HiCustomer Welcome to JA. I am Buddy, and i will try and help you out.

 

What is your engine serial number and also the last 6 of your truck vin # ?

 

Thanks
Buddy

Customer: replied 4 years ago.
Engine ser 5EK90454 last 6 of vin 946818
Expert:  Buddy replied 4 years ago.

Thanks for the info.

 

The vehicle speed sensor wires are at pin location 12 and 18 of the vehicle harness at your ecm. Here is also a diagram. DIAGRAM <<<<<< click there for wiring diagram and go to page 2.

I hope this helps you out. If you have 2 sensors or 1 four wire sensor, then 2 are going to the ecm and the other 2 are going to the speedo. If you just have 1 two sensor, then the ecm gets the vehicle signal and then sends it the speedo head. If you have anymore questions, just ask.

 

Thanks
Buddy

 

I



Edited by Buddy on 2/19/2010 at 7:57 PM EST
Customer: replied 4 years ago.
We have one sensor with 2 wires that go to the ecm we changed the speed sensor and tried a new speedo still the same we have no speed reading until about 30 miles are put on the truck we have power to the head ( speed o fuse) we show voltage from the ecm to the speedo head via pin #16 9.58 volts , when we check the neg pin from the ecm (#10) we have -9.58 volts out of the ecm to the speedo head does that seem right
Expert:  DR.Cummins replied 4 years ago.
your in good hands now.
Expert:  Buddy replied 4 years ago.
Thanks for the information.

Does your speedo head show the correct speed when it reaches 30 or is the speed way off?
Does the speedo head have dip switches on it?
Was truck doing same thing before anything was replaced?


Thanks
Buddy
Customer: replied 4 years ago.
The truck was doing this when it came in that was the reason it came in as far as the rate from what the driver has told us it is real close or right on ( using mile markers) and it does have dips on the back and we set the new one to the old one we were wondering if someone changed them at one point as the customer recently bought this truck and it has been doing this since he got it. Can not get any info from previos owner
Expert:  Buddy replied 4 years ago.
Thanks for the reply.

If the speedometer does not work, till it reaches about 30 mph and the speed is pretty accurate and it happens like this every time. This would eliminate a dip switch issue. Normally speed is off when the dip switches are set wrong. That would also eliminate the pulses per mile setting in the ecm also.You replaced the speedo head and the speed sensor, so that eliminates those 2. I have seen on peterbuilts when you replace speed sensor to the newer style sensor, you would have to get a short little pigtail harness with a resistor in it from pete before the speedo would work correctly. I have only seen that in petes tho. If all of the wires ohm out good, i would be trying to hang a test ecm on truck and seeing what it did. I hope this helps you out. If you have anymore questions or info, just ask.

Thanks
Buddy
Customer: replied 4 years ago.
It does not start at 30 mph it starts working after the truck has gone 30 miles or so , PS we do not have a test ecm
Expert:  Buddy replied 4 years ago.
Thanks for clearing that up with me.

How many wires are in the plug at your speedo head.

Buddy

Edited by Buddy on 2/20/2010 at 4:50 PM EST
Customer: replied 4 years ago.
There is a 6 wire plug into the back of the head
Expert:  Buddy replied 4 years ago.
Thanks for the reply.

I dont know what the 6th wire would be. Normally you have both your wires coming from the ecm. Then a hot and ground,and another hot for the light when lights are on.

I would ohm all wires and look for a open. I would figure your problem is between the ecm and the speedo head, ecm, or a hot or ground problem to the speedo head. It should be coding if it was a problem between the speed sensor and the ecm.

Thanks
Buddy
Customer: replied 4 years ago.
We ohmed out all of the wires they ohm out fine as far as coding the terminal on the ecm for diagnostic is broken off into the plug so there is no codes showing , we have power a good ground the two from the ecm ohm out between the ecm and the head the sixth wire is just a pig tail 6 inches long goes no where , some one said if the dips are in the wrong place it would not know when to start reading i thought it was just fo calibration , we are leaning towards somthing in the ecm and after it heats up it starts to work we do not want to buy a ecm and be wrong.
Expert:  Buddy replied 4 years ago.
Thanks for the reply.

Everytime i have seen dip switches off, it throws the speed off. I have seen that the new speedo heads have different way dip switches. I have seen on alot of trucks when you put the new speedo head in, the dip switches are completly opposite. I would try that, if that did not work i would flip them back to where they are now. If there is 10 dip switches also, i can try and give you the correct setting, just keep up with the originals just incase. I would need rear end ratio and tire revs. If you could just mark the tire and ground and move the truck one tire rev and measure the distance. Normally around 11 feet. Give me that reading also.

On the ecm, you might be able to get a ecm programmed in test mode from a cat dealer and try it. If that didnt fix it, the ecm would automatically blank out in 24 hours if serial number was not put in. If it did not work, you could take it back. Thats how we do it at my work, but i dont know if that is how they do it for the public or not. Might try calling and seeing.

I hope that helps you out.Let me know what you come up with.

Thanks
Buddy
Buddy, Technician
Category: Heavy Equipment
Satisfied Customers: 730
Experience: 20 years experience. Freightliner tech for last 14 years
Buddy and 4 other Heavy Equipment Specialists are ready to help you
Customer: replied 4 years ago.
We took the ecm out and cleaned all of the pins and the speedometer is now working not sure for how long as there seems to be corrosion inside the connection on the ecm also there was a broken pin ( for the diagnostic light ) probably why there was no code thans for the help
Expert:  DR.Cummins replied 4 years ago.
ok
Customer: replied 4 years ago.
You did not answer my question I asked for a wiring diagram
Expert:  DR.Cummins replied 4 years ago.
i know and i opted out.
Customer: replied 4 years ago.
That is why I paid buddy , thans maybe next time
Expert:  DR.Cummins replied 4 years ago.
i know

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