Southampton diesel Posted December 16, 2015 Share Posted December 16, 2015 Hi all, I am brand new to this forum, but have found lots of useful info already. I have a 2004 Mack cx613 that is experiencing low power. It started out of the blue. With an unloaded trailer it struggles to get to 50 mph. Low boost pressure also. The only fault code in it is road speed voltage to high. I changed the sensor and now my speedo works but same low power same code. Just wanted to ask some more seasoned Mack guys if I'm going in the right direction looking into that fault code. I traded my Volvo in on this one and now I'm having regrets. Any help would be much appreciated Quote Link to comment Share on other sites More sharing options...
turckster Posted December 16, 2015 Share Posted December 16, 2015 If you still have an active fault for the speedo then it will derate HP and speed. Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 16, 2015 Author Share Posted December 16, 2015 Thanks for the response. That's what I was gleaning towards. Just not to sure on where to go it's got a spn85 fmi 4 fault. Which is voltage less than normal. Before I changed the speed sensor it was a different fault. I'm just not sure where to look next. Both wires are reading .2 volts. I'm not much of a Mack man, but from reading earlier posts there are sure a bunch of you on here Quote Link to comment Share on other sites More sharing options...
turckster Posted December 18, 2015 Share Posted December 18, 2015 I would begin by removing the passenger side kick panel. It houses the VECU and ABS modules. The FMI:4 is low voltage or short to ground, The kick plate is metal and the harness wires are notorious for rubbing/chaffing on the cover. I would check the wires and make sure everything looks ok there. If all looks good then you need to measure the resistance between pins VJ2-11-1.0 and VJ2-10-1.0. These are on the Vj2 connector on the VECU, the wires are labeled and the VECU has VJ1, VJ2 and so forth labelled on the cover next to the connectors. The resistance of the circuit should be nearly the same as the sensor-approx 140-180 ohms. Most that I've measured were around 160-170 ohms. If that checks out ok then measure pins VJ2-10 and VJ2-11 against all other pins on the VECU including ground, all should be open circuits. If you find continuity in a circuit outside the two for the sensor then you have a short to that circuit. Now the fun begins....finding the short.Most likely its shorted to ground somewhere. My guess would be the VECU/ABS cover or on top of the transmission somewhere. I'll post a picture of the wiring diagram for the sensor circuit, its crude but it works: Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 21, 2015 Author Share Posted December 21, 2015 Thanks so much for the detailed post. I was away for a few days but I'm going to dig into it now I'll keep you updated Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 21, 2015 Author Share Posted December 21, 2015 Well I have some interesting news. All the wires look good. Pins ten and eleven have no resistance at the plug at all. Nor are any pins shorted with another wire. I believe this is going to be a project. Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 21, 2015 Author Share Posted December 21, 2015 Not sure how there is no continuity yet the speedo is working! Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted December 21, 2015 Share Posted December 21, 2015 Is this a four wire sensor? Quote glenn akers Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 21, 2015 Author Share Posted December 21, 2015 No just a two wire. I went through the great previous info top to bottom and have no continuity between the two. My check engine light would come on and off last month but the truck ran great. Then all of a sudden the light stayed on and the truck lost substantial power Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 21, 2015 Author Share Posted December 21, 2015 Does anyone know if both wires go through the bulkhead connector? I realized the wires at the speed sensor have different numbers on them. So my guess is those wires tee off, one set to speedo one set to ecm. I'm pretty much learning as I go along haha Quote Link to comment Share on other sites More sharing options...
turckster Posted December 22, 2015 Share Posted December 22, 2015 The wires go directly to the VECU. The speedometer gets its info from the VECU. After looking at the diagram again I realize I mislead you. You should be measuring pins VJ2-11 and VJ2-12 for speedo sensor resistance and these pins vs all others to make sure there are no shorts. Sorry about that, blond moment I guess. Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 22, 2015 Author Share Posted December 22, 2015 I realized that last night also. I have moments like that myself. Especially the older I get. I'll dig into at some point today Quote Link to comment Share on other sites More sharing options...
MackFarmer05 Posted December 22, 2015 Share Posted December 22, 2015 (edited) If that doesn't work then you may check your boost sensor. We had one go out and it showed little to no boost but it was actually telling the ECM it was over boosting. New sensor fixed it. Edited December 22, 2015 by MackFarmer05 Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 22, 2015 Author Share Posted December 22, 2015 Thanks for the reply Mack farmer. My boost sensor was irradic so I did change it. But I'm still getting the low voltage code for the speed sensor. And still have no continuity between vj2 11 and 12. I did notice the wires at the speedo are vj2 9 and 41-a-8.0 Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 22, 2015 Author Share Posted December 22, 2015 And still low power. I just don't understand how the speedo is working and I'm showing no continuity Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 22, 2015 Author Share Posted December 22, 2015 Gotta love my luck. It seems this Mack is wired differently than it should be. I found continuity on vj2 9 but the lettered wire I cannot find Quote Link to comment Share on other sites More sharing options...
Southampton diesel Posted December 22, 2015 Author Share Posted December 22, 2015 Gotta love my luck. It seems this Mack is wired differently than it should be. I found continuity on vj2 9 but the lettered wire I cannot find Quote Link to comment Share on other sites More sharing options...
turckster Posted December 24, 2015 Share Posted December 24, 2015 VJ2-9 and 41-A-0.8 are for PTO #1 switch. I believe the wrong connector is plugged into the speedo sensor. Find the wires labeled VJ2-11 and VJ2-12 on top of the trans and plug it into the speedo sensor. The speedo may be working because it is getting its reading from the ABS module. The ABS module gets its speed reading from the right front steer axle sensor. Quote Link to comment Share on other sites More sharing options...
TotoCh613 Posted August 1, 2018 Share Posted August 1, 2018 Hi, there. Im also new to this forum, Im having a similar situation after a shop installed a rebuilt transmission and clutch, its a mack ch613 1997 427hp, my speedometer is not working and I don't have any power!!, electronic malfunction light is on and code is 4-2. I bought a new speed sensor, installed it and checked the tone ring last night and nothing still have the same problem... I wonder if you guys can give me some ideas on what could it be. Thanks! Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted August 1, 2018 Share Posted August 1, 2018 Check all connections and wires for damage and put your eyes in connectors for terminals backed out or damaged. Assume they stretched your harness, which can cause an invisible internal separation in the wires. They swapped rear output yoke, so make sure pickup ring is tightly compressed below yoke shoulder and not loose(or missing). Make sure your adjusted (gapped) properly at sensor. In the good old days drivers would disconnect the Speedo pickup to over ride governed speed. In the not so good ol days the computer recognizes the Speedo loss as an attempt to manipulate the governing so it derates your power as a “ha ha” maneuver. Good luck! Quote Link to comment Share on other sites More sharing options...
Hobert62 Posted August 1, 2018 Share Posted August 1, 2018 4 hours ago, Mack Technician said: In the not so good ol days the computer recognizes the Speedo loss as an attempt to manipulate the governing so it derates your power as a “ha ha” maneuver. Them bastards! Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted August 1, 2018 Share Posted August 1, 2018 17 minutes ago, Hobert62 said: Them bastards! Manipulative, control freak, underhanded, narcissistic, corporate "Yes-men", engineering Bass Turds! 1 Quote Link to comment Share on other sites More sharing options...
Hobert62 Posted August 1, 2018 Share Posted August 1, 2018 (edited) Our freightliners will shut off if the speedo quits working. Edited August 1, 2018 by Hobert62 1 Quote Link to comment Share on other sites More sharing options...
Mack Technician Posted August 1, 2018 Share Posted August 1, 2018 Makes you chuckle a bit when your calling for a five hour (warranty) tow, from the deep end of the Upper Peninsula, for a cheesy sensor. Not so funny once the warranty has expired. Quote Link to comment Share on other sites More sharing options...
TotoCh613 Posted August 2, 2018 Share Posted August 2, 2018 Found the problem, (code 4-2)with my speedometer not working and low power. After a clutch and transmission installment. When they changed the transmission, someone plugged the female conector from speed sensor (on the back of the transmission)into a wrong male plug wire.....it fitted perfectly ! Got under the truck and found a hanging wire near the back of the transmission unplugged the speed sensor from that connector and plugged back to this other one BAM ! It works now.... Thanks guys ,this is a great forum. 2 Quote Link to comment Share on other sites More sharing options...
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