2004 Pete 379 C15 speedo issues

corneileous

Well-Known Member
Hey guys, been having a problem with the speedometer on this truck ever since I’ve had it which is now been for probably around four or five months and everything the mechanic’s done to try to fix it hasn’t changed anything at all.

When I first started driving it, on average, it’s about 30 miles an hour too slow. It works, but at normal highway speed it shows I’m doing 30 miles an hour when my Garmin says I’m doing 70 but if I accelerate up to like 80 miles an hour, it may show 35 miles an hour on the speedometer and so far what the mechanic has tried, they put a new speedometer in it and calibrated it to the gear ratio and all that stuff but nothing changed; he claims that he replaced both of the speed sensors that’s on the back of the transmission and still, nothing has changed. He put the original speedometer back in after supposedly replacing both speed sensors and still, nothing has changed.

He even tried playing around with the calibration with the little switches on the back of the new speedometer but yet again, nothing really has changed so what would possibly be the problem? I’m thinking maybe it’s got to be in the wiring harness on one or both of those speed sensors that may be doing something but I don’t know? Any ideas? Thanks.
 

corneileous

Well-Known Member
Last six of the s/n?

Either the dip switches are incorrect or its a 70 pin ecm with a single speed sensor and calibration should be done in the ecm.
Serial number of the speedo itself?

The rest of that, I don’t know. I’d probably have to crawl under there again but the last time I looked, I thought I saw two speed sensors. The cruise still works though, if that helps.

But just in case it wasn’t implied, the new aftermarket speedo is what’s in there now and has been ever since. I asked him about the original speedo but he thinks another mechanic swiped it and put it in another truck, or somethin, I dunno. Lol.
 

pushbroom

Goldmember
Premium
Serial number of the speedo itself?

The rest of that, I don’t know. I’d probably have to crawl under there again but the last time I looked, I thought I saw two speed sensors. The cruise still works though, if that helps.

But just in case it wasn’t implied, the new aftermarket speedo is what’s in there now and has been ever since. I asked him about the original speedo but he thinks another mechanic swiped it and put it in another truck, or somethin, I dunno. Lol.

Last six of the truck s/n. That will tell me engine/ speed sensor setup
 

pushbroom

Goldmember
Premium
Truck has a BXS CAT in it. There is only one speed sensor on the back of the trans. Speed goes directly to the engine ECM then out from there to the speedo in the cab.
Dip switches on the back of the speedo should be set to 1,3,9,10 in the On position.
The actual speed sensor calibration is done in the engine ecm.
Verify dip switches are correct then it needs to get hooked up to a laptop to set the speed calibration.
 

corneileous

Well-Known Member
Truck has a BXS CAT in it. There is only one speed sensor on the back of the trans. Speed goes directly to the engine ECM then out from there to the speedo in the cab.
Dip switches on the back of the speedo should be set to 1,3,9,10 in the On position.
The actual speed sensor calibration is done in the engine ecm.
Verify dip switches are correct then it needs to get hooked up to a laptop to set the speed calibration.
Ok, thank you.

But like I was saying, since this speedo is an aftermarket one- not sure what the brand is, I’ll attach a pic but the dip switch positions is the same for this speedo, correct?

And also, what is the calibration procedure? I thought that my mechanic already would have done this but is it just as simple as using the laptop to input tire size and rear gears? Anything else? Again, thanks for your help, it’s mucho appreciated.
 

corneileous

Well-Known Member
Forgot to attach the photo....lol.
 

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corneileous

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Ok so, the fist picture is how the dip switches were set.... the second one was to what you said to set them at.... third just shows the brand and other information about the speedo.
 

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pushbroom

Goldmember
Premium
Ok, thank you.

But like I was saying, since this speedo is an aftermarket one- not sure what the brand is, I’ll attach a pic but the dip switch positions is the same for this speedo, correct?

And also, what is the calibration procedure? I thought that my mechanic already would have done this but is it just as simple as using the laptop to input tire size and rear gears? Anything else? Again, thanks for your help, it’s mucho appreciated.
Your speedo is just the updated amatek 900 series. Dip switches work the same on all of them.

Your dip switches now look correct.

Yes just need to input the ppm pulses per mile.
Tire size and rear gear calculation. That may already be correct, the dip switches being incorrect could have caused your issues. Take it for a spin and see how it is
 

corneileous

Well-Known Member
Your speedo is just the updated amatek 900 series. Dip switches work the same on all of them.

Your dip switches now look correct.

Yes just need to input the ppm pulses per mile.
Tire size and rear gear calculation. That may already be correct, the dip switches being incorrect could have caused your issues. Take it for a spin and see how it is
Well, I’m not really sure exactly what my mechanic did finally this weekend but after a quick phone call to him after I got in my truck this morning, took off and noticed that speedo is pretty damn dead on now, he said that the calibration for the tire size and all that was just way off and I asked him, I said why was it off so much and he said well probably because since this last bunch of trucks they bought were all oil field trucks that they had them deliberately backed off on purpose so they wouldn’t be racking up as many miles which, I thought was a little far-fetched but irregardless, he made it sound like he took your advice, left the dip switches alone on the speedometer and only concentrated on the calibration so a big thank you to you for your help, and whoever it was who tagged you to come in here… LOL.
 

Rigjockey

In Gord we trust!
Truck has a BXS CAT in it. There is only one speed sensor on the back of the trans. Speed goes directly to the engine ECM then out from there to the speedo in the cab.
Dip switches on the back of the speedo should be set to 1,3,9,10 in the On position.
The actual speed sensor calibration is done in the engine ecm.
Verify dip switches are correct then it needs to get hooked up to a laptop to set the speed calibration.
For you this must be very simple. For me this is very impressive!
Good job! :thumbsup:
 

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