MACK321 Posted February 10, 2023 Share Posted February 10, 2023 (edited) I have a 2011 Mack cxu613 w/MP7. I am having an issue with the Speedo randomly dropping out which cuts power. If stop & kill the truck & wait for all the instruments to turn off then start back up the Speedo then works until it randomly does it again. The fault light does not come on. If you are going down the highway when this happens I can just turn the key off until all instruments turn off then turn back on & it returns to normal until next time. Very random - 5 minutes, 15 minutes or maybe even 45 minutes apart. Replaced speed sensor and speed sensor harness truck been to 5 shops no one can figure it out couldn't get up to 45mph loaded please help me Edited February 10, 2023 by MACK321 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/ Share on other sites More sharing options...
Onyx610 Posted February 10, 2023 Share Posted February 10, 2023 What trans do you have? Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525040 Share on other sites More sharing options...
Onyx610 Posted February 10, 2023 Share Posted February 10, 2023 Sounds like the vecu is losing communication with the vss. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525042 Share on other sites More sharing options...
MACK321 Posted February 10, 2023 Author Share Posted February 10, 2023 Onyx610 I have eaton fuller transmission 13speed Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525057 Share on other sites More sharing options...
Joey Mack Posted February 10, 2023 Share Posted February 10, 2023 Have you checked the ground connections down below the fuse panel? You may be able to pull the panel around the throttle pedal, and reach up to get to them. There is also ' pass through connector's ' in the firewall.. all those ground wires are gray.. 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525061 Share on other sites More sharing options...
MACK321 Posted February 10, 2023 Author Share Posted February 10, 2023 Joey Mack i haven't done that I will check that for sure tomorrow Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525063 Share on other sites More sharing options...
Onyx610 Posted February 10, 2023 Share Posted February 10, 2023 I’ll see what other info I can find on this issue as well. Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525065 Share on other sites More sharing options...
MACK321 Posted February 10, 2023 Author Share Posted February 10, 2023 Please thank you anyone that figures out my problem you will be gifted Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525066 Share on other sites More sharing options...
Onyx610 Posted February 10, 2023 Share Posted February 10, 2023 Not needed. Gift will be getting you back on the road. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525067 Share on other sites More sharing options...
Joey Mack Posted February 10, 2023 Share Posted February 10, 2023 Yeah !!!! What Onyx said... 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525068 Share on other sites More sharing options...
Joey Mack Posted February 11, 2023 Share Posted February 11, 2023 Just curious?? What is not the solution?? I'm losing my MP knowledge quickly. However, I still work on trucks here and there.. jojo Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525086 Share on other sites More sharing options...
Joey Mack Posted February 11, 2023 Share Posted February 11, 2023 I expect that you are on target.. I am a grounds checking guy.. I have chased many issues, way back,, only to find a bad ground or even a blown fuse... I was trying to show off at times, only to find the issue was simple.. so now i toss out the simple stuff.. jojo 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525089 Share on other sites More sharing options...
Onyx610 Posted February 11, 2023 Share Posted February 11, 2023 (edited) Id like to see Mackpro in on this one for this guy. However for the hell of it can you check engine hours on the instrument cluster and see if you get a bunch of dashes? Edited February 11, 2023 by Onyx610 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525091 Share on other sites More sharing options...
Joey Mack Posted February 11, 2023 Share Posted February 11, 2023 Just for kick's.. I'm going to stay with a bad ground or a chaffed wired shorted to ground.. I don't mind if I'm wrong here at BMT.. because there alway's is someone who nails it down, and solves it.. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525092 Share on other sites More sharing options...
Onyx610 Posted February 11, 2023 Share Posted February 11, 2023 (edited) What’s odd is that shutting the truck off resets the truck and all is fine. I wonder if the instrument cluster module is going out of it or abs sensor(s). Let’s have him check easy and free things first though. Id like to see some other ideas on this too. Edited February 11, 2023 by Onyx610 Spelling. Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525093 Share on other sites More sharing options...
Joey Mack Posted February 11, 2023 Share Posted February 11, 2023 A bad relay that gets hot can do that, but to crank right back up??? yeah, I see your point.. Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525094 Share on other sites More sharing options...
Onyx610 Posted February 11, 2023 Share Posted February 11, 2023 Well hopefully we can get him back to 100 percent. Sounds like he really needs the help. Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525095 Share on other sites More sharing options...
Joey Mack Posted February 11, 2023 Share Posted February 11, 2023 Yep. Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525096 Share on other sites More sharing options...
Solution Hot oiler Posted February 11, 2023 Solution Share Posted February 11, 2023 12 hours ago, Onyx610 said: Sounds like the vecu is losing communication with the vss. i had exact same issue, turns out it was the rear axle anti lock wheel speed sensors. if they don’t match up to the transmission speed sensor it causes exactly what you are saying to happen. 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525098 Share on other sites More sharing options...
Onyx610 Posted February 11, 2023 Share Posted February 11, 2023 36 minutes ago, Hot oiler said: i had exact same issue, turns out it was the rear axle anti lock wheel speed sensors. if they don’t match up to the transmission speed sensor it causes exactly what you are saying to happen. Thanks hot oiler! This is what we need. You are very correct on the abs wheel speed and correlation with vss. It will cause a derate. He claims to have no codes. Did you have any? 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525099 Share on other sites More sharing options...
Mackpro Posted February 11, 2023 Share Posted February 11, 2023 Most of the time it’s a ABS wheel speed sensor issue. You will get the lighting bolt with both ABS and ATC lights on if this is the cause . If only the lighting bolt comes on and absolutely no ABS/ATC light comes on when this happens. Then pull the center floor mat and floor board out ( 10 mm socket) , real easy to do , push the shifter boot through floor board. Carefully follow the trans harness towards the driver side and you will see a 10 or 12 pin connector ( 2 rows of 5/6) . Look for rubbed wires near this connector. Do be afraid of cutting zip ties and pulling the wires up and looking underneath them . I had 2 of our 2014-15 CXU’s have shorted wires in this area. It was due to who ever pulled the trans to change the clutch, didn’t zip tie up the connector and both rubbed on the braided air compressor line. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525104 Share on other sites More sharing options...
Onyx610 Posted February 11, 2023 Share Posted February 11, 2023 (edited) Not sure what brake system you have but try this. https://www.anythingtruck.com/instructions/060-WS24ServiceDataSheet.pdf Edited February 11, 2023 by Onyx610 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525137 Share on other sites More sharing options...
MACK321 Posted February 11, 2023 Author Share Posted February 11, 2023 So picked up my truck from the shop brought it home went straight to the rear axle speed sensor found that the speed sensor is bad on the rear passenger side gonna wait Monday to get parts to replace it when I unplug it I lose my speed I hooked it up to the driver side and so far it hasn't messed up with the passenger side not hooked up hope that makes sense I'm not a handy guy but you guys made me work on my truck and big help thank you guys I hope this is the problem 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525139 Share on other sites More sharing options...
Hot oiler Posted February 11, 2023 Share Posted February 11, 2023 14 hours ago, Onyx610 said: Thanks hot oiler! This is what we need. You are very correct on the abs wheel speed and correlation with vss. It will cause a derate. He claims to have no codes. Did you have any? no i did not - but not sure what may have been turned off in the cumputer my mechanic replaced both sensors - but his discription was that they were out of position to the point they could not have worked. i have i not looked at the position of these since he worked on it but i almost wonder if i could have possibly bent a bracket while changing brake shoes 🤷♂️ 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525140 Share on other sites More sharing options...
Onyx610 Posted February 11, 2023 Share Posted February 11, 2023 4 minutes ago, MACK321 said: So picked up my truck from the shop brought it home went straight to the rear axle speed sensor found that the speed sensor is bad on the rear passenger side gonna wait Monday to get parts to replace it when I unplug it I lose my speed I hooked it up to the driver side and so far it hasn't messed up with the passenger side not hooked up hope that makes sense I'm not a handy guy but you guys made me work on my truck and big help thank you guys I hope this is the problem You got this! Check out the Bendix stuff for reference. The sensors will come with instructions too. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/72498-speedo-randomly-dropping-out/#findComment-525141 Share on other sites More sharing options...
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