Abs & brake light

[fritzcartage]

Having a problem with my 07 mega. ABS, BRAKE and CEL came on. Now speedo and exhaust brake dont work. Truck has h&s xrt with dpf delete pipe. Pulled codes p063c-generator voltage sense low, uc121-i think is an abs module code, p0501-vehicle speed sensor 1 performance, p0532-air conditioner pressure sensor low, p0169-water in fuel detected. P063C, P0532, P0169 are old codes that needed to be cleared out from previous work done to the truck. The ones i'm concerned with are the uc121 and P0501. I think i'm going to need to replace the speed sensor/sensors or abs sensors. But am unsure of there locations and dont want to replace anything that doesnt need to be. Has anyone ever run into this problem before?

 

[p-Bar]

If your speedo is dead do the speed sensor first should fix the problem

 

[Bob4x4]

With that many sensor codes check wiring first,many sensors share supply voltage

 

[fritzcartage]

Everything started working normally very soon after I started this thread, I just attributed the problems to the very cold weather we were having. Then I smoked the transmission and had it rebuilt. Anyway we put it back in last nite and the speedo doesn't work and the abs lite is back on and the brake lite is on too, also the check gages lite is on. Pulled the codes: uc121 - lost communication with antilock brake module, p063c - generator voltage sensor low, p0501 - vehicle speed sensor performance. I have replaced the speed sensor on top of the differential and cleared the codes and they come rite back. 5 months ago I had the cummins repair shop in Chicago replace the head gasket on the truck and adjust the valves. When they did this they left all 4 of the battery terminals loose which caused me to lose both batteries, replaced them and all seemed fine. Over the next couple days I noticed the truck was charging less and less and then finally no charging. 1 month prior to the truck going to cummins we had replaced the alternator. So I took off the alternator and brought it in to the rebuilder, who is right around the corner from our shop, and they said the whole inside was destroyed. I asked if it was possibly from the battery terminals being left loose and they said definitely. They rebuilt it and we reinstalled it. I don't know, could that have damaged the computer? The check gages lite has been on this last 5 months. I don't know what I should try next. I checked all the fuses and they're all good. Maybe abs sensors? Any advice greatly appreciated.

 

[fritzcartage]

I cant believe it. In the time it took to type all that, after I got done I got up from the computer walked over to the truck and cleared the codes 1 more time. This time they have not come back. I don't know if I just had to clear them a bunch of times or what. I'm gonna lower the truck down and take it for a test drive. I hope they don't come back again.

 

[fritzcartage]

Just got back from test drive and no CEL, no ABS lite, no BRAKE lite, and the speedo works, however the check gages lite is still on. Voltmeter on the truck says less than 14 volts. Hooked up the battery charger/voltmeter at the shop and it says 13. 5 volts, so its still charging just not very much. Maybe that's why the check gages lite is on. Anyone know what these things are supposed to charge at?

 

[fritzcartage]

Yup 20 min later and theyre back. Its gotta be a voltage/wiring issue. Im headn 2 the gin mill. I need it.

 

[p-Bar]

It should be charging to about 14. 4 volts

 

[fritzcartage]

Have load tested both batteries and they're both good. Found some corrosion on the wire to the fuse block, cleaned that up. Checked all battery connections and they're ok too. Today the bat charger/volt meter says it's charging at 14. 3 volts. Still have all the same problems p0501 - speed sensor performance, p063c - generator voltage sense low, uc121 or u0121 - lost communication with abs module. On Monday I am going to try a new alternator and see if that does any good.

 

[cerberusiam]

Check and make sure you did not pick the harness on the firewall when you replaced the transmission. Also, check the harness thouroughly for ANY suspicious rubbing or scuffing. If you pinch or short the trans control wires you will get all manner of electrical gremlins.

 

[fritzcartage]

OK. Have cleaned and reinstalled (even though they looked ok) the driver side ground wires on the fender and the frame and no changes in codes detected. Inspected all wiring looms from trans reinstall and all are ok. Inspected all other looms and they also appear in good order. Today I replaced the alternator and have a change in the codes. No longer spitting the code p063c for generator voltage sense low and the CHECH GAGES light is off. However still spitting the p0501 - speed sensor performance, u0121 - lost communication with abs module, and CEL, ABS & BRAKE lights are still on, and the speedometer still doesn't work. Now I am really leaning toward the pcm unless there's another sensor somewhere I have missed that controls abs and the speedo? Forgot to mention also installed new front and rear pads and rotors. I inspected the abs sensors on the front bearings and nothing out of the ordinary. I may end up bringing it to the dealer before I replace the computer just to be sure. Hopefully someone will have a better idea to point me in a different direction. Thanks to all for reading and answering.

 

[cerberusiam]

Have you replaced the speed sensor on the transmission? Your truck doesn't use the ABS sensor for speedo it still uses the speed sensor.

For the ABS, on the frame above and in front of the axle should be a connector for the ABS harness. Make sure it is still plugged in, wires not broke, and the pins clean.

 

[fritzcartage]

Thanks for replying cerb. I have not replaced the speed sensor on the trans, I was unaware of it. For the connectors on the abs sensors, I did check to see if those were ok and they were. All connected and clean inside. When I called the parts store to order the speed sensor they only told me there was one that was located on top of the diff housing. Maybe I should try calling the dealer and ordering the speed sensor on the trans. I assume it's located near the tailshaft. I remember installing some wire looms back there on the trans reinstallation. I should be able to get it out without pulling trans, shouldn't I?

 

[fritzcartage]

I have ordered the other speed sensor on the trans from the dealer. It will be in Wednesday morning. Hopefully will solve the problem. Thanks for the help. Will update the post when I get it installed.

 

[cerberusiam]

I keep thinking you are working on the 96 in your sig.



If it is your 07 thats different. The oput shaft speed sensor usually doesn't throw that code but who knows. You also have sensors and wiring on the both front wheels on the 07. Possibly one of them is bad?

 

[fritzcartage]

Update on my issue. Installed the new speed sensors on the trans and still had the same problems. Then went into the hospital with a ruptured appendix. Finally got out and back to work on the truck. Figured it was beyond my capability so took it to the dealer. They determined that the abs module was defective. They replaced it and all is well. Thanks to all for the advice.