U1040

[BrianF]

Alright gents, I borrowed an OTC Genisys from a friend of mine to dig further into my abs/brake light on issue with my 2006 4.2.

I had posted some of this years ago but for a refresher, spring of 2020 or so, driving around in the slush and snow, the abs and brake light would randomly come on and off. Eventually staying on. I cleaned the ground on the frame under the driver area. The ground was rusty but no change when cleaning it. I had cleaned it a few more times since, including daisy chaining a ground wire to a couple other grounds. No change.

Next I tried cleaning the contacts in the ignition switch. This caused the CAD motor to quit, along with the blower fan. New switch, which I believe was the new light colored one was put in. The CAD and fan were back working but still the brake and abs lights on.

Thw e brake switch works as it will chime as soon as you pull the handle.

Brake fluid level is good and they have been flushed a couple times in the last 5 or so years.

So, ECBM..... doesn't look like the ones on the videos but looks to be right in front of the fuel tank, driver side. There is one large connector, which I am leary to mess with as the little lever or cam lock broke off. The electronics look to be accessible with four torx once the connector is removed.

Is it a logical step to remove the connector and dig in?

 

[TJBaker57]

Alright gents, I borrowed an OTC Genisys from a friend of mine to dig further into my abs/brake light on issue with my 2006 4.2.

I had posted some of this years ago but for a refresher, spring of 2020 or so, driving around in the slush and snow, the abs and brake light would randomly come on and off. Eventually staying on. I cleaned the ground on the frame under the driver area. The ground was rusty but no change when cleaning it. I had cleaned it a few more times since, including daisy chaining a ground wire to a couple other grounds. No change.

Next I tried cleaning the contacts in the ignition switch. This caused the CAD motor to quit, along with the blower fan. New switch, which I believe was the new light colored one was put in. The CAD and fan were back working but still the brake and abs lights on.

Thw e brake switch works as it will chime as soon as you pull the handle.

Brake fluid level is good and they have been flushed a couple times in the last 5 or so years.

So, ECBM..... doesn't look like the ones on the videos but looks to be right in front of the fuel tank, driver side. There is one large connector, which I am leary to mess with as the little lever or cam lock broke off. The electronics look to be accessible with four torx once the connector is removed.

Is it a logical step to remove the connector and dig in?

This U1040 code is a loss of serial data issue, not any operational issues of the EBCM.

This can be caused by a loss of momentary loss of power or ground to the EBCM.

I would say every connection, fuse, fuse socket, switch, and so on having to do with power and ground to the EBCM needs to be checked. Also the single serial data wire to the EBCM should be inspected.

Oddly, I see no U1040 listed but instead see U1041?? Understanding how the DTC is coded it still applies.

U1041 — 2006 Chevy Truck TrailBlazer 4WD L6-4.2L VIN S Service Manual | Operation CHARM

Detailed repair manual for the 2006 Chevy Truck TrailBlazer 4WD L6-4.2L VIN S.

charm.li

 

[BrianF]

Thank you. I recall seeing various other codes related to the internal ecbm solder issues. In retrospect, a sig al loss would fit with my original onset, being intermittent while driving through slush and snow.

To make this more fun, I need to get the TB a bit higher off the ground than just ramps as I am not some skinny kid anymore. Also, the wire looms are packed with dirt and debris. I'll have to see what one can do to trace the wires from that ecbm connector.

 

[BrianF]

Got the connector off. Pins all look clean, as do the wires entering the connector.

I dont have a diagram handy but key on, engine off, the two main positive connectors each have 11.5v (battery is low at 12.05v. The two main grounds each have low resistance, maybe half an ohm? Do not recall... but, the ground was checked using the frame ground assigned to the ecbm.

 

[BrianF]

Since I was torn down that far, pulled the board out. Had to clean the torx bolt heads with a pick as there was a layer of corrosion. Hit the connectors with contact cleaner and compressed air. Inspected the circuit board, which "appeared" fine from the best I could tell.

I am not sure who makes this ECBM so I am limited on researching known issues. There is plenty online about the various kelsey hayes.

Cleaned some grounds again but no changes. I assume the ignition switch is good as the power is supplied to the ECBM is there.

Next I will have to see about removing the wire loom to try and find any shorts or wire breaks.

 

[TJBaker57]

dont have a diagram handy but key on, engine off, the two main positive connectors each have 11.5v (battery is low at 12.05v. The two main grounds each have low resistance, maybe half an ohm

The trouble is it can test fine when you are checking. But driving down the road you hit a good bump or the like and say the fuse is loose in the socket or there is a crack in a copper wire in one of the fuseblocks and the power is interrupted momentarily. In just 5 seconds that code sets.

This is one reason why electrical issues can be so frustrating.

 

[BrianF]

Moose had linked the service manuals, which I dug into. I found the pin outs on the connector. Pin 5 is serial data signal but further reading says I will need some sort of scope as its a sine wave of sorts.

Now, this one I missed, so I will either tap into the wire or pull the connector again. Pin 32 is ignition voltage. So dumb me needs to know its output. I assumed the main positives of 31 and 2 were ignition tapped. Perhaps they are and perhaps they are not.

Then further reading says that the ignition switch can cause low voltage to the ECBM among other systems. Tomorrow I will check some suggested fuses in the rear block. If they show low, then test the orange wire at the ignition.

 

[TJBaker57]

Pin 5 is serial data signal but further reading says I will need some sort of scope as its a sine wave of sorts.

Not at all. The U1040 or U1041 code is set when a 5 second time period elapses where no "State of Health" message is transmitted by the EBCM.

To my knowledge no scope is going to tell you precisely what messages are being sent, or even who is sending them.

We read of these SOH (state of health) messages in SI and their importance, but who knows what they even look like??

Well here they are below, read by a low cost OBD2 adapter and an Android device.

Highlighted, beginning with "14:44:44.496 08 FF 29 03 8F" which is sent from the EBCM as evidenced by the "29" right after the "FF".

Note the timestamp and the time that elapses between this message and the next one with the very same data. It's just under 2 seconds as the data specification demands.

If 5 seconds elapses between these messages the U1041 (or U1040) sets.

The same rules apply to all these other SOH messages highlighted here. Every module is required to send these messages EVERY 2 seconds or less. If they don't then a loss of communications code sets for that module (assuming their data is critical to vehicle operations).




The trouble is determining WHY are messages not getting sent on time. I would want to know that power and ground are reliably present at ALL times of vehicle operation.

One power source is always hot regardless of key position. A second power source is hot ONLY in the RUN key position.

A momentary loss of either power wire can cause this sort of issue.

A poor connection of the EBCM serial data wire can also cause trouble. The serial data wire runs from the EBCM through the C101 connector near the underhood fuseblock to the SP205 splice pack.



Does this U1040 code return quickly if you reset/clear codes?

 

[BrianF]

Very interesting and indeed a learning moment for me. As for the return of the code? I cleared everything and it either never cleared or it returned in very short order.

 

[TJBaker57]

Very interesting and indeed a learning moment for me. As for the return of the code? I cleared everything and it either never cleared or it returned in very short order.

If the U1040 returns very quickly that would at least suggest the trouble is more prevalent. In theory that should make it easier to diagnose as opposed to chasing something that may only happen for a few seconds every few weeks.

I will have to research a little but I sort of think that if the communications from the EBCM is missing right from the key ON it sets a different code, and not the U1040.


I saw a forum post from some time ago where you commented on Torque Pro and an OBD2 adapter. Did you purchase these or no?



If you have the OBD2 adapter I could instruct on how to listen in on every message the EBCM sends. That could be useful in tracking down a loose connection.

I have a PCM, BCM, and TCCM in a drawer here in the kitchen set up with power and an OBD2 adapter. Those who know me would not be surprised by this.

Anyway, seen below I told my OBD2 adapter to show all messages pertaining to "Network Control". This is where those SOH messages are addressed. Since there is nothing happening, no engine running or the like this "system" is as would be seen if a key was left in the RUN position for a long time. Essentially idle but ready for action. The modules present on the network are all dutifully sending their SOH messages.

Then I stopped that request and told the adapter to show me everything sent by the TCCM. So there we see only the TCCM messages.


Were I chasing a intermittent fallout of TCCM messages I could do this same exercise and while monitoring the messages on the phone I could go around all the various connections, fuses, wiring looms, etc. and wiggle stuff to see if I got the messages to stop. Presumably if I wiggle a bad connection I might see the messages cease for a few seconds or so.

 

[BrianF]

@TJBaker57 Thank you again for your insight. I cleared all codes again this morning and the U1040 returned right away.

I never did get the a Bluetooth OBD2 as I ended up with 3 other scanners..... currently using that OTC Genisys.

I checked voltage at the orange ignition wire, key on, which showed low 11v range. I checked rear fuses, key on and all were low 11v.

I pulled the EBCM connector and checked pin 32, positive Key on. It showed low 11v range.

 

[TJBaker57]

never did get the a Bluetooth OBD2 as I ended up with 3 other scanners..... currently using that OTC Genisys.

Unless one of those scanners can show the kind of data I mentioned then you are stuck repeatedly checking here and there for the source of the issue, with no real evidence of the SOH message.

As an alternate to the method I posted,,, if one of your scanners can display live data from the EBCM.... you "might" be able to set it up displaying said live data and then wiggle wires, connectors, etc. here and there. The scanner just "might" complain if the data drops out??

From a little reading I think if the EBCM SOH traffic is entirely not there from the getgo a U1000 code would set. I think the U1040 only sets if SOH messages are initially received but then cease for a time?

Anyone else have any thoughts on this?

 

[mrrsm]

This is a Useful Thread concerning a broad range of EBCM Diagnostic Step By Steps from a different Forum (including the U1041 Trouble Code) ... but still involving the GMT360 Platform that may be useful in investigating the U1040 Issue and possible Class II Communications Interruption:

Electronic Brake control module failure??

www.tbssowners.com

...and conceptually... This Video shows how to remove and re-install the Sealed Heat Sink Cover during the refreshment of the Logic Board Connections that might require Re-Soldering with TRUE Lead (Pb) Solder as another attempt at reviving the fairly expensive GM-GMC EBCM Units to prior normalcy:

 

[BrianF]

Thank you for the read. Mentioned in that is that low voltage can cause U codes. Now, what constitutes low voltage? I was regularly getting a low 11v range at the pins. Perhaps I should grab another ignition switch as the new one could be faulty or even one of the pins on the connector is garbage..

 

[Mooseman]

If the voltage stays low while it's running, then definitely investigate that further. Low voltage can cause all sorts of funky things with these trucks. I've got an old Impala at work that the battery got weak and cranked really slow but it started. However, it threw a bunch of lights at me and the power steering didn't work. After letting the battery charge a while, it was fine.

 

[BrianF]

I will dig further into the battery as well. I never did check running voltage. While it still starts fine, the battery is at least 12 years old and frozen at least once a few years back.