Mac 2 Posted March 14, 2022 Share Posted March 14, 2022 I just bought the truck with this issue it has code 4-1 speed sensor engine is derated low power I replace the speed sensor 1 turn back out after bottoming out as it says the old one was plastic had a lot of oil and grease on it so the ring is not loose I repaired the oil leak and went ahead to test drive and still speedometer not working and still no power I don't have a wiring diagram to trace the problem. Quote Link to comment https://www.bigmacktrucks.com/topic/69383-2003-mack-r688s-e7-350-8ll/ Share on other sites More sharing options...
Joey Mack Posted March 14, 2022 Share Posted March 14, 2022 try this,,, see if the wires at the sensor are broken up stream. if that doesnt show results, the white wire at the sensor plug has the circuit printed on it... for example: VJ-1 - 22- 0.5.... that means: VECU plug number 1, pin number 22. wire size in .05.. the wire size is no biggie, but you can trace the wire using the code, and you can un-plug the VECU plug and ohm out the wire. yes you will need to make an extension wire, but its do-able. you put the DVOM on 'audible' and wiggle the wires along the harness, and listen for the ringing to stop, then you can locate the weak point in the circuit.. Quote Link to comment https://www.bigmacktrucks.com/topic/69383-2003-mack-r688s-e7-350-8ll/#findComment-492140 Share on other sites More sharing options...
Joey Mack Posted March 14, 2022 Share Posted March 14, 2022 Here is a quick look at the VECU. this is what you have... jojo Quote Link to comment https://www.bigmacktrucks.com/topic/69383-2003-mack-r688s-e7-350-8ll/#findComment-492141 Share on other sites More sharing options...
Joey Mack Posted March 14, 2022 Share Posted March 14, 2022 on top left of the tranny, is a wide rectangular plug. that should be where the speed sensor wires are . notice VJ2 #11 and VJ2 #12... those are the wires for the sensor. jojo Quote Link to comment https://www.bigmacktrucks.com/topic/69383-2003-mack-r688s-e7-350-8ll/#findComment-492142 Share on other sites More sharing options...
doubleclutchinweasel Posted March 14, 2022 Share Posted March 14, 2022 Dude! You continually amaze me with your knowledge of these things and your ability to help people work on them! 1 1 Quote "Eagles may soar, but weasels don't get sucked into jet engines." Link to comment https://www.bigmacktrucks.com/topic/69383-2003-mack-r688s-e7-350-8ll/#findComment-492152 Share on other sites More sharing options...
mowerman Posted March 14, 2022 Share Posted March 14, 2022 You should provide a Joey the genius website with a pay as you go option that way you could just sit in the house with the heat and dogs and stay clean…,. Come on????!!!!! . Bob 2 Quote Link to comment https://www.bigmacktrucks.com/topic/69383-2003-mack-r688s-e7-350-8ll/#findComment-492168 Share on other sites More sharing options...
Joey Mack Posted March 14, 2022 Share Posted March 14, 2022 you guys are very kind... I really care about every one here and the newbies. and if I have the info, I am glad to post it.. it's a brotherhood.. and there are so many smart guys here, all 3 of you guys as well, and we ALL give our knowledge.. This is fun for me and I have never been that guy in the shop that wont tell the secrets... Jojo 1 1 Quote Link to comment https://www.bigmacktrucks.com/topic/69383-2003-mack-r688s-e7-350-8ll/#findComment-492170 Share on other sites More sharing options...
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