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new speed sensor truck won't start? - hosetrucking - 02-04-2019
2009 Peterbilt 388 ISX and 18 speed eaton. The last few months the cruise control and speedometer quit working anytime there is rain. Initially I thought of the junction where all the wires come into the cab, cleaned that up and still the same problem when it rains. Everything else works fine. So then I thought maybe it's just the speedometer sensor or wires. I followed the wires from the speedo sensor on the back of the transmission up towards the harness by the firewall where a bunch of other wires join together. I found a few minor breaks in the wiring as well as some corrosion around the sensor. I went to replace the sensor and it broke apart on me. I was able to slowly chip away and extract the broken pieces of plastic out of the sensor port. I have been driving around the last week with no sensor and aside from lack of cruise, speedo, and jake it has started up and ran just fine. Today I finally get the new sensor, install it, and put new wiring all the way up to the firewall and now the truck won't start via the starter. I now have to roll start the truck. I removed the new wiring and new sensor and still it won't start on it's own. Any suggestions? Do I need to reset something? Thanks, Adam.
RE: new speed sensor truck won't start? - imalumberjack - 02-04-2019
Checked the fuses?
RE: new speed sensor truck won't start? - Waterloo - 02-04-2019
Check the cab for leaks?
RE: new speed sensor truck won't start? - hosetrucking - 02-04-2019
Thank you for the responses. I have the truck running and can't turn it off at the moment to check the ignition fuse and relay. The speedometer, engine brake, cruise and everything else is working fine now that the sensor and wires have been replaced. Now the only problem is that the starter will not engage. The fuel pump and everything else turns on but the starter won't turn over. Now I have to push start the truck. Never had a problem with the starter until the moment I put the new sensor in. However now the starter won't turn over whether the sensor is plugged in or not. Being that I have not had any problems with the starter until the moment I put the new sensor in, I'm assuming it has something to do with it, however maybe it's just coincidental. And for the record the starter is only 10 months old so I'm assuming it's still ok. And the only reason it was replaced 10 months ago is because I had a new rear engine seal / rear block subframe put on and so just had them replace the starter while they were they at it. Other then that, I've never had a starter failure on this truck in the last three years I owned it. Thanks again for any suggestions.
RE: new speed sensor truck won't start? - Waterloo - 02-04-2019
With the truck running, take a screwdriver and whack the ECM with the handle of it, see if anything happens.
RE: new speed sensor truck won't start? - Waterloo - 02-04-2019
Also, have you checked the cables running from the battery box? Long story, but I had to replace over 100 feet of cabling in my 2008 ProStar. From the factory the cable was missing the jacket, all of my cable, ground and power was green. Something you may want to look at if you have not.
RE: new speed sensor truck won't start? - Nilao - 02-04-2019
Check the clutch switch...just unplug it and jumper it. If it starts, replace switch. If not you could have a faulty starter relay. Peterbilt uses a ignition relay as well as a starter relay. My friend had this issue so i had him swap the ignition and starter relays.
Truck would then turn over but not start...a new relay fixed his issue.
RE: new speed sensor truck won't start? - hosetrucking - 02-04-2019
Thanks Waterloo. All the cables are good going to and from the battery box.. Nilao, thanks, this truck does not have a clutch switch for starting. It will start whether the clutches in or out and even if it's in gear it will try to start. The only clutch switch on it is for breaking the cruise control. As far as the relays go there are two main access relays. One of them is clicking the other one is not. I swapped out relays and it's the same thing, the one in the back is still clicking in the one in the front is not. I'm going to have to go get a new multimeter since my old one is not working and then slowly trace the wires. I'm still not sure if replacing the speedometer sensor had anything to do with the truck not starting but I've never had any other truck starting issues until the minute I put that speedometer sensor in. Since then it won't start whether the speedometer sensor is plugged in or not but I don't know if plugging that in has anything to do with the crankcase positioning sensor and if so if the ECM just has to be reset?
RE: new speed sensor truck won't start? - Waterloo - 02-04-2019
Try hitting the ECM with the screwdriver handle... ;-)