3 communication errors U1000, U1021, & U1045

[Hatchet]

So got my truck towed to the mechanic last night because the truck died while driving and wouldn't start but would crank. Happened once before with EricSS and we thought it was fuel pump. Just got call back saying the fuel pump is fine.

But I it does has 3 communications errors. U1000, U1021, and U1045. He said its the computer is not communicating correctly with the fuel pump and the ignition switch. Of course he recommends it needs to go to the dealership to get it fixed. Would need new ignition switch (with some astronomical price attached to it) and the computer would need to be wiped and reprogrammed.

So what are the experts opinions on my options right now. I don't have alot of experience with communication errors. So all help is appreciated.

 

[The_Roadie]

Any of the intelligent modules on the data bus could have failed, or the data bus could have a short or open. That's why the two splice packs were put into the data wiring.

 

[Hatchet]

So trying to replace the ignition switch probably wouldnt do it. It could be anything... 2 splice packs?


U1000 - Invalid or Missing Data for Primary Id
U1021 - SCP (J1850) Invalid or Missing Data for Air Conditioning Clutch
U1045 - SCP (J1850) Invalid or Missing Data for Traction Motor

I know the AC isn't working as when we replaced the engine, I have a leak in the system that i can't find. The traction motor, I have no idea what in the vehicle uses a traction motor.

 

[AtlWrk]

First, you need to get your truck away from that mechanic. Reprogramming the PCM? BS

Ignition switches are relatively inexpensive and bad ones are known to cause a whole host off odd electrical behavior. If you haven't changed yours yet it wouldn't be a waste.

I know you have codes but do you have a CEL as well?
I ask because these types of errors typically do not disable the vehicle--they MAY just be coincidental.

U codes are manufacturer specific and GM changes the device IDs from year to year so it's safe to assume the ac clutch and traction motor references in the generic DTC list are erroneous.

For a 2006: U1016 = PCM, U1026 = Transfer Case Control Module, U1041 = Brake Control Modue, U1064 = Body Control Module. Since you're in that same range I would guess your codes refer to two of those 4 modules.

 

[Hatchet]

First, you need to get your truck away from that mechanic. Reprogramming the PCM? BS

Ignition switches are relatively inexpensive and bad ones are known to cause a whole host off odd electrical behavior. If you haven't changed yours yet it wouldn't be a waste.

I know you have codes but do you have a CEL as well?
I ask because these types of errors typically do not disable the vehicle--they MAY just be coincidental.

U codes are manufacturer specific and GM changes the device IDs from year to year so it's safe to assume the ac clutch and traction motor references in the generic DTC list are erroneous.

For a 2006: U1016 = PCM, U1026 = Transfer Case Control Module, U1041 = Brake Control Modue, U1064 = Body Control Module. Since you're in that same range I would guess your codes refer to two of those 4 modules.

They are a decent mechanic, but i have a feeling when he looked up the issue in the system, it said that and take to chevy dealership.

That is the first thing I was gunna do is replace the ignition switch.

The first time this happened i checked many times and no DTC was found, this time around i didn't check.
He said something about the PCM is not communicating with the ignition switch and fuel pump. Which does seem odd.

The only spots I could find U codes for chevy, they all listed those items as those codes.

Well ignition switch is first to try, i know those can cause all kinds of crazy things. Just wanted everyone elses opinions.

 

[Hatchet]

So went to get the truck back to my house. Called them they ran out and said it started so drove it back, it didn't die. Hotness and I replaced the ignition switch and now i'm just praying.

Last time it happened, when it finally started, it was about 2 weeks till it acted up again. So No idea if its fixed and that was the issue or not till if it dies again. And since I know nothing about the serial data system in these trucks, I might just have to take it to the dealership if it acts up again. I don't want to, but I have no idea what to do to narrow down what the issue could be.

Oh and no DTC codes are present at all, pending or full.

 

[C-ya]

Hatchet, there are a few threads where someone (roadie, gmcman, moose?) has added pics of the splice packs and their locations. The normal routine is to find the splice and unhook it. Drive to test as normal and see if you get the fault/symptom back. If you do, plug that splice pack back in and remove the other one. If it does not come back (whichever splice pack you have removed), start pushing pins out of the splice pack for individual components until you isolate the one that is causing the issue (use a wiring diagram/pin out chart to know which pin to push). It could also be one of the grounds that a component uses that is related to one of the splices. The ground locations have been posted as well.

If you have a TechII or the like, it will speed things up. Does your mechanic have one and know how to use it?

Caveat: I'm not sure if any of the modules on the data bus would prevent proper operation of the vehicle. Someone who has dealt with this (calling roadie!!) may be able to interject some sanity into this.

 

[The_Roadie]

Caveat: I'm not sure if any of the modules on the data bus would prevent proper operation of the vehicle. Someone who has dealt with this (calling roadie!!) may be able to interject some sanity into this.

ANY of the modules on the bus, including ones you might not suspect like the radio or TCCM, can send garbage messages that drown out/interfere with valid messages. Since the BCM and the PCM especially have to talk at start-up time for the security function to allow the vehicle to run, those two can't be disconnected as part of the troubleshooting process.

That's why you should never just totally disconnect either of the splice packs. I would try the one-wire-at-a-time process. Pulling the whole metal shorting comb out of the connector might be useful if you have a wiring harness problem (short to ground or open) to troubleshoot, not a bad module type of fault.

 

[Hatchet]

Hatchet, there are a few threads where someone (roadie, gmcman, moose?) has added pics of the splice packs and their locations. The normal routine is to find the splice and unhook it. Drive to test as normal and see if you get the fault/symptom back. If you do, plug that splice pack back in and remove the other one. If it does not come back (whichever splice pack you have removed), start pushing pins out of the splice pack for individual components until you isolate the one that is causing the issue (use a wiring diagram/pin out chart to know which pin to push). It could also be one of the grounds that a component uses that is related to one of the splices. The ground locations have been posted as well.

If you have a TechII or the like, it will speed things up. Does your mechanic have one and know how to use it?

Caveat: I'm not sure if any of the modules on the data bus would prevent proper operation of the vehicle. Someone who has dealt with this (calling roadie!!) may be able to interject some sanity into this.

I found the schematics. Can't believe I never saw them listed before. I never knew anything about the data system but now i'm learning. No they don't have a tech 2, they have some snap on tablet engine diagnostic. Hoping one of the guys on here is getting the Tech 2 like he told me he mite.

I can also see cause the vehicle to not run. What seemed to be the issue (to the best of my knowledge) is the fuel pump wasn't being sent power to turn on. So a cross, overload, wrong, or missing data in the data stream could cause it to die out and stop sending the signal to the pump saying run. I'm hopeful that the ignition switch was the issue and that changing that will be the fix. Just got off expressway and everything seemed normal. I'm just gunna be on edge for the next few weeks while driving it.

 

[The_Roadie]

When the BCM doesn't get a valid message through to the PCM at start-up time, the way it works is to suppress the fuel pump.

 

[Hatchet]

But would it kill it while driving? or only at start up?

 

[The_Roadie]

Not sure. Shop manual only goes into a certain depth of theory.

 

[Hatchet]

Hmmm Guess i need to push out line M on SP205 and test theory.

 

[Hatchet]

Update: So far its been running normal since replacing the ignition switch.

 

[Hatchet]

Retraction of previous statement. It failed on me again on my way to work this morning. Luckily it died out only 2 houses away, and a nice guy from the apartments across the street helped me push it back to my driveway. Damn these things are heavy when they are all dead weight. So it looks like I'm gunna have to go get reamed over at the GM dealership...

 

[Sparky]

U1000 is a generic "bad data" code. Can be thrown if any serial data device screws up and spews garbage and/or doesn't respond. From a GM TSB on another issue:

These DTCs set when the control module does not receive a message that it was expecting from another control module, and does not know which control module did not send that message.

If the DTC U1000 or U1255 set current, this usually indicates a module that is currently not communicating or a configuration issue.
For example, if the control module is configured for an option (ie: Onstar, Keyless Entry, Memory Mirrors, etc.) that the vehicle does not have, it may expect to receive a message regarding this missing feature. This would usually occur due to the control module being recently replaced and incorrectly setup.

When the DTC U1000 or U1255 is current, the module that is not communicating may not even be listed on the Tech 2 on the Diagnostic Circuit Check/Class 2 Message Monitor list.
If the DTC U1000 or U1255 has set in history without other DTCs, replacing the control module setting the DTC is most likely NOT the solution. The module that has set the code is looking for an input from another module that is not communicating. Since the module did not receive an input that it is expecting to see, it sets a U1000 or U1255 which indicates there was a loss of communications.

So my guess is the other two (U1021 and/or U1045) point to the device(s) that are the problem. Now just the trick is finding WHAT those are... Trying to track that down. Seems they are a guarded secret by GM or something.

Maybe pull a splice pack and just check all the connections?

 

[Cloudsurfer]

I have a B1000, which appears to be SRS related?

 

[Hatchet]

Yea i got the wiring diagram for the splice packs. Just when the truck dies, is when i'm in a hurry to somewhere. Then by the time i can get around to doing it, its working fine. So can't determine which item is the issue, let alone what line of the 2 splice packs it is. Maybe when I get home from work today it still isn't working. Then I just gotta deal with the single digit temperatures and play around.

There is talk from another member that the ignition cylinder could be a cause of issue to. improper connection to the ignition switch, or something like that. Mite try that but don't know yet.

And those damn U codes are kept more secret then area 51...

 

[Hatchet]

Ok I got home hoping it wouldn't start so I can diagnose. Nope it started. Backed it to the garage and did some back and forth and it did one but would restart. It only died in drive not reverse.

The 21 code says ac system communication code so I just removed the fuse and relay for it and didn't die out on me. But I'm thinking it Mite have to do with the security system (keyless entry). Will that kill power to the fuel pump? If so I couldn't find which fuse controls it. I gotta search the site better later tonight to find it as my keyfob battery keeps dying after a month or so.

 

[Hatchet]

Well untill the next failure I have removed the fuse and relay for the AC system. See where it goes from there... And since I don't know where in this vehicle is a traction motor, That will be the next to figure out.

 

[dfc739]

Well untill the next failure I have removed the fuse and relay for the AC system. See where it goes from there... And since I don't know where in this vehicle is a traction motor, That will be the next to figure out.

FYI- when I was troubleshooting my similar electrical problem with the splice packs pulling fuses and relays wasn't good enough. The splice packs are for communication and data transfer, not to supply power. In order to properly troubleshoot you must pull the wires from the splice packs. It's pretty easy to pop them out with a set of small screwdrivers. My problem involved wires shorting to ground which garbled all the data being sent.

 

[Hatchet]

Thanks for the tidbit. I figured no power, no data. Guess I was wrong.

 

[Hatchet]

Ok I am thoroughly confused and about to give up. This morning truck wouldnt start but i had a side job to do. Came back and luckily it still wouldn't start.

Found SP205
No start
Disconnected 205 and it started after the 3rd try.
reconnected it and no start.
Disconnected 205 and it would not start again.
Confused....

Found SP206
No start
Disconnected 206 and it started on first try.
Reconnected it and no start.
Disconnected 206 and it would not start again.
More confused...

Disconnected both 205 and 206 and it would not start.
Reconnected both and it would not start.
Still confused...

any ideas? Did I do something wrong? Cause i'm at a lost more now then I was when I started.

 

[The_Roadie]

The splice packs aren't meant to be disconnected fully. They're just a place where you can remove individual comm wires using guidance from the schematics. The BCM and the PCM must always remain connected since the security function is shared among them.

 

[Hatchet]

Ok I thought if one was disconnected it whittle tell me which line it is along. So I did it wrong. Thanks for the info

Edit. So is there one I should not disconnect at all? Like the dark blue with the white stripe? Or are all fair game?

 

[The_Roadie]

Get the schematics to confirm the color codes. Leave the PCM and the BCM connected. Everything else is fair game.

 

[Hatchet]

I've already had that printed. But that's what I need to know. Thanks as always Roadfather.

Edit. Just thinking out loud. If I leave 205 connected and disconnect 206 and it still doesn't start, I can eliminate 206 items. Ok I got an idea of the correct way to do it now.

 

[Hatchet]

Well now it gets better. Hoping the 0* weather doesn't have anything to do with this.

I removed each pin one at a time and still no starting on anyone of them. So I don't know what it could be.

Theoretically if I left everything un pinned and only had the PCM and BCM attached, would it start?

 

[Hatchet]

Put in New computer. Still same.

 

[Hatchet]

View attachment 32310
There goes the sign of a defeated man. On its way to the dealership. Forgot to put up the white flag on it.

 

[Sparky]

Man that sucks. Hope they find it quickly without it costing too much!

 

[Hatchet]

Still at square one. Finally was able to get the fuel pump in and tank back in. Made it half a block and it died and would not start. I'm out of my mind.

I sat and stared at the truck for an hour running everything though my head and i'm no where closer then I was when this started.

Engine cranks, fuel pump relay is activating. Fuel pump is not sending the fuel.

I replaced the fuel pump, CAM sensor (on the word of a friend of being a possibility), ignition switch, switched PCM with one i got from PCM4less programed to my truck. Still the same issue from when it started.

I don't know anymore. Every mechanic I have talked to, GM or not, just go to fuel pump and won't go any further. I've lost all hope. No one that ive talked to knows anything to do. Ive tried every diagnostic possible that has been mentioned but still nothing.

 

[Sparky]

Relay gets power. Does the pump get the power? Maybe the pump harness is going bad? Mine shorted on me a year or two ago and it was blowing my PCM fuse (they run the pump off the PCM circuit...).

 

[Hatchet]

Relay gets power. Does the pump get the power? Maybe the pump harness is going bad? Mine shorted on me a year or two ago and it was blowing my PCM fuse (they run the pump off the PCM circuit...).

The relay is activating on the turn key. But hear nothing from the fuel pump. I am thinking about running a constant 12V power to the fuel pump to see if that will let it run. But I am worried about causing more damage to the everything doing that. I'm not blowing any fuses. I will have to check them again, but the original issue I checked all of them and nothing was blown. It would randomly work and randomly stop working and not restart.

 

[Texan]

Just a thought on my part. I have not had any problems with my TB, so this is
my experience on another GM vehicle. The wiring connector for the fuel pump
underneath the car near the fuel tank had hard to see corrosion on the contacts.
I cleaned them with contact cleaner and use dialect grease and that solved the
problem. I an attaching a picture of a TB fuel pump that shows a harness with
it for the TB.

More Information for DELPHI FG0387

 

[Sparky]

The relay is activating on the turn key. But hear nothing from the fuel pump. I am thinking about running a constant 12V power to the fuel pump to see if that will let it run. But I am worried about causing more damage to the everything doing that. I'm not blowing any fuses. I will have to check them again, but the original issue I checked all of them and nothing was blown. It would randomly work and randomly stop working and not restart.

Yeah if you're having harness issues they aren't the exact same as I had, but you may just be getting a broken circuit vs a short.

 

[MAY03LT]

I am thinking about running a constant 12V power to the fuel pump to see if that will let it run. But I am worried about causing more damage to the everything doing that.

So now I know what the post in the what did you do thread was about.

Pull the fuel pump relay and you wont mess anything up. Jump the gray wire at the pump with 12v, and if it still won't run, jump the black wire at the pump to ground. Don't jump the orange/black or purple wires with anything or you're gonna have a bad time.

 

[Hatchet]

So now I know what the post in the what did you do thread was about.

Pull the fuel pump relay and you wont mess anything up. Jump the gray wire at the pump with 12v, and if it still won't run, jump the black wire at the pump to ground. Don't jump the orange/black or purple wires with anything or you're gonna have a bad time.

Ok as long as I won't damage any thing. I'll try that tomorrow.

 

[Hatchet]

Ok so I did the ground first. Nothing.

Did the 12 volt from the rear fuse block. Nothing.

Disconnected everything and it tried to start. But not enough.

Either I have no spark or I got a bad fuel pump out of the box. I need to grab a spark tester to test for spark before I take out fuel pump again... FML

 

[MAY03LT]

How were you doing the jumping? The reason that I ask is that it is very rare for a pump to be DOA (unless it's a crapanapa pump).

The connector should be plugged in with a t-pin (or a small paperclip) backprobing the gray wire. This pic isn't of the fuel pump connector, but the idea is the same: