[FIXED] 2007silverado 5.3l ABS light on u0073 and c0040

so this truck came in with ABS light on u0073 and c0040 check for powers and grounds all checked ok im able to comunicate w/module checked com. lines and im getting 2.7v on HI+ AND 2.3 ON HI- which im assume these are good readings. found that EBCM is not sending 12v to the RFspeed sensor so replaced EBCM and reprogrammed it truck did ok for couple of days well is back with same codes need help please

Thanks for letting me know about posting this. It helps.
Without doing research for you (I can't right now). Can you give me the definition of both of these codes?
Also, are you again missing the 12v supply/signal to the one WSS?
Why would it be fixed for a few days after EBCM replacement? The only explanation of that is you moved something (wiring) in the process of testing and disconnecting the EBCM. Or, just by disconnecting power to the EBCM, that circuit came back to life, again, suggesting that 12v supply wire to the WSS is touching ground somewhere intermittently and the reason it came back was because of the reset. (I call this "intentional shut-down" in my classes)

thanks for your prompt response u0073 is control module communication bus off. c0040 refers to RF wheel speed sensor circuit. i did a continuity test on the wires and checked ok i get continuity im still little confuse on checking for shorts but if i supply the 12v to the sensor looking at data the sensor starts working and it shows the same speed changes as the LF. now if the EBCM doesnt send the 12v how do I make it come alive again? I hope you can help on this one no rush thanks man by the way love your channel it has helped a lot

I have seen similar symptoms on the Bosch 5.7 ABS, system performs a sanity test on all the sensors at key on. If a sensor fails it would shutdown the 12v supply to that sensor ony. On that vehicle it turned out to be a corroded pin in the ABS unit harness plug.

Like Andy mentioned, I've also seen this ABS system take the 12V feed away if it doesn't like what it gets back on the signal wire. Honda will do the same thing. For whatever reason, I've found many corroded wires within a few inches of the WSS connector on this generation of truck, front AND rear. I know that the ohm meter says all is well, but you can try backing that up by using a test light to load the wires (provide power/ground yourself, WSS and ABS disconnected). Then give the wires a gentle wiggle and see if the light flickers.

now if the EBCM doesnt send the 12v how do I make it come alive again?

This is the right question to ask! In addition to the above, I've also seen these modules act this way when the battery gets run low. The low system voltage throws them for a loop, and causes the module to stop supplying the 12V to one or more sensors. Disconnecting the battery cables and shorting them together for a little while got the modules working again. Some form of 'logic lock' or another. :silly:

Is the battery weak on this truck? If the owner has been running the battery dead, then this problem could be self-induced.

cool i will definetly try that the only thing that was kicking my behind is the missing 12v on a sensor. i let you guys know thanks

thanks Tyler for the tip this kind of info becomes pretty handy since i couldn't find it anywhere else as i mention before didn't think that EBCM would quit sending the 12v if it sees a problem. Now im almost sure I am dealing with a wiring issue although my continuity test says the contrary. i will keep you guys posted thanks

No problem! I dunno if the service info says anything about how the 12V feed driver works, but it's a weird strategy to run into if you're not looking for it.

Let us know what you find.

Like everyone said you will lose the 12v if the EBCM detects a sensor or wiring fault. Here is a waveform of a 2010 pickup that would randomly set a wheel speed sensor code. The bad spot doesn't look like much but after speed sensor replacement the waveform was very clear cut like the good spot in the waveform.

quick test clear codes. unhook left front speed sensor. front probe it use jumper wires to the right front vehicle harness. check scan data spin tire. that tells you wiring integrity, module processing of the speed sensor.

thanks to all your replies guys specially to those that mentioned about the shut down on the 12 v from EBCM to the sensor. So it ended up been a bad sensor but it is worth reading what happened and the mistake I made. this is a regular customer, truck has 300k miles, about 4months ago i had replaced both front wheel hubs assy. (with sensor included) one of the bearings had failed. Anyway customer brought truck in because of an ABS light been on, scanned it and retrieved U0073 and C0040 cleared codes and light went off but had a pending u0073 couple of days later light came back on and both codes were present again (u0073 and c0040) went to my data PIDS and noticed that RF sensor was not reading at all so order another hub and plug it in I turned it by hand while watching data and still no changes on my scanner, pulled wiring diagrams and found that EBCM supplies 12v to the sensor so found that i was not getting 12v i checked the other side and i had 12v so went straight to module and sure enough no 12v to RF sensor but i had 12v to LF. NOT KNOWING ABOUT THE SHUT DOWN i immediately suspected a bad module. replaced it and reprogrammed it light went off and no codes present, 2 days later it comes back with same symptoms. that is when your expertise play a big roll and decided to replace the sensor and this time I did what you suggested and disconected the battery and shorted both wires for a little while. truck has been FIXED. Never really suspected of a bad sensor due to it was a fairly new sensor, aftermarket of course. thanks to every one of your replies. by the way where do you get all the good info from like the shut down on modules? i use prodemand and i dont remember reading anything about it, unless i missed it.






ly

Glad to hear it! Definitely isn't easy when the service info let's you down, eh?

I learned about 12V feed thing because I came very close to changing an ABS module on one of those trucks. :blush: For the same reason, missing a sensor power feed. It was a body shop car, and the battery had been run low during repairs.

I'd made the replacement call, but decided to try a soft reset just for giggles. Plugged everything back in, and got the feed back. Surprised the crap out of me! That's when I figured out that the sensor feeds are on some kind of high side driver circuit.

Bumping this thread with additional info for anyone searching in the future. I stumbled across a GM PI that details a fantastic test for determining if a missing 12V sensor feed is due to intentional shutdown, or a wiring/EBCM issue.



Cliffnotes version: Turn the key off, connect a DMM across an unplugged WSS connector. Turn key on, watch for a brief 12V pulse. If the pulse is there, the lack of 12V is intentional shutdown. If it's not, check the wiring before calling an EBCM.

This parallels SD's approach to intentional fuel injector shutdown - cycle the key and see if you get injector pulse back.

Any meter you used would have to be very fast to catch the initial 12v test pulse, it really needs a scope with the trigger set for a single shot capture. if after power up self-test I don't see power to the sensor and there is no obvious wiring or connector issue. although it is not 100% certain it is a pretty good bet it is the sensor so for the Bosch BMW system with Blue connectors I have a known good sensor that I can connect for a very quick test.

You're absolutely right, it needs to be a fast meter. :ohmy: The PIP mentions the Fluke 87, so I'm guessing GM feels like it's fast enough to catch it while in Min/Max mode. If in doubt, scope it.