Robd1225 Posted December 15, 2020 Share Posted December 15, 2020 Have 2 mack trucks both throwing pid 84 fmi 5 road speed code both have new sensors checked at vecu resistance is 157.6ohms not sure why they keep throwing code Quote Link to comment Share on other sites More sharing options...
Vmac3 Posted December 15, 2020 Share Posted December 15, 2020 What year are the trucks? Quote Link to comment Share on other sites More sharing options...
Robd1225 Posted December 19, 2020 Author Share Posted December 19, 2020 2006 if I check at vecu I have 159 ohms if I plug in the vecu connector it goes up to 190ohms key on Quote Link to comment Share on other sites More sharing options...
Vmac3 Posted December 19, 2020 Share Posted December 19, 2020 Sorry, I should of asked earlier. What model trucks are they? Quote Link to comment Share on other sites More sharing options...
Vmac3 Posted December 19, 2020 Share Posted December 19, 2020 The code is saying that the current is low and or open circuit. The speed sensor circuit has 2 dedicated wire that are twisted together. Since its a series circuit, any added resistance to the circuit would decrease the amount of current flowing through the circuit. With the key off, disconnect the J2 plug at the VECU. Disconnect the speed sensor and jump the two terminals at the sensor with a wire. Measure the resistance at the J2 plug at pins 11 and 12. The resistance should be very low with continuity. With one lead on pin 11, check to see if any other pins with the other lead is shorting with pin 11. Do the same with pin 12. Should take only a few minutes. If that is okay then there is a square connector on top of the transmission that would get loose. Give that a shake and see if the resistance value changes. If it does, open the connector and check the pins. If they are okay put a zip tie around the two halves of the connector and secure nice and tight. Let us know what you find. There are a lot of smart people here that can chime in. V 1 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted December 20, 2020 Share Posted December 20, 2020 Just curious.... is the tranny yoke loose..? 1 Quote Link to comment Share on other sites More sharing options...
Vmac3 Posted December 20, 2020 Share Posted December 20, 2020 1 hour ago, Joey Mack said: Just curious.... is the tranny yoke loose..? Good point. If the tranny yoke is loose then the tone ring will slip. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted December 20, 2020 Share Posted December 20, 2020 Heck, I also forgot to ask if its a Mack tranny... the tone ring may be pressed onto the yoke, Eatons have a separate tone ring, in this year model. just like the FRO 15,16,210C tranny's ive put synchros in... Correct me if i'm wrong, Vmac3.. Jojo Quote Link to comment Share on other sites More sharing options...
Vmac3 Posted December 20, 2020 Share Posted December 20, 2020 I remember that the older Mack trannys were pressed on with the yoke where they were inside the bearing cover. Can't really say I remember. Its been a long time now. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted December 20, 2020 Share Posted December 20, 2020 It's all good.. I feel sure the tone ring is pressed on in Mack tranny's. His series would be a 300, not much different from 200's... there are some slight differences, the 4th 5th sliding clutch is fine splined like an eaton. otherwise its similar to 200's. Multi speed reverse adds a different set-up in the back box with caged reverse idlers...... anyway, a loose yoke could cause the code... its great to chat with you, Jojo 1 Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted December 20, 2020 Share Posted December 20, 2020 I also forgot to ask if the sensor is "set" right... ( all the way in, then one full turn out)? 1 Quote Link to comment Share on other sites More sharing options...
Robd1225 Posted December 24, 2020 Author Share Posted December 24, 2020 Thanks everybody for the help harness jumped out at Sensor fron pins 11 and 12 got .01ohms was great until key on is when it changed ran out of time and had to put vecu panel back together and code cleared after that probably a chaffing wire up at vecu somewhere it has a eaton trans and yes speed sensor set correct no on the loose yoke. Have not had come back on yet 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.