TROUBLE CODES U1026 AND U1041

[JOE2003]

I have a 2000 silverado 4x4 that is giving me the codes u1026 and u1041 what could cause this prolem and i also have a hard starting problem every now and then i was thinking it was the fuel pump but iam not sure know with these codes showing up

thanks for any info on this problem

[roberson104]

DTC U1026 Loss of ATC Class 2 Communication

Circuit Description

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring (Node Alive messages). A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that module's "Node Alive" message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a "Node Alive" message every two seconds. When no message is detected from a learned identification number for five seconds, a DTC U1xxx (where xxx is equal to the three digit identification number) is set.

 

The Control Module ID Number list provides a method for determining which module is not communicating. A module with an internal class 2 serial data circuit malfunction or which loses power during the current ignition cycle would have a Lost Communication DTC set by other modules. The modules that can communicate will set a DTC indicating the module that cannot communicate. When no message is detected from a learned identification number for five seconds, a DTC U1xxx (where xxx is equal to the three digit identification number) is set.

 

Control Module

ID Number

 

ATC

026

 

BCM

064

 

EBCM

041

 

EVO

192

 

IPC

096

 

PCM

016

 

SDM

088

 

VCM

016

 

VIU

016

 

 

When more than one Loss of Communication DTC is set in either one module of in several modules, diagnose the DTCs in the following order:

 

Current DTCs before history DTCs unless told otherwise in the diagnostic tables.

The DTC which is reported the most times.

From the lowest number DTC to the highest number DTC.

Conditions for Running the DTC

Voltage supplied to the module is in the normal operating voltage range (approximately 9 to 16 volts).

Diagnostic trouble codes U1300, U1301 and U1304 do not have a current status.

The vehicle power mode (ignition switch position) requires serial data communication to occur.

Conditions for Setting the DTC

A messsage from a learned identification number has not been detected for the past five seconds.

 

Conditions for Clearing the DTC

A current DTC will clear when a "Node Alive" message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.

A history DTC will clear upon receipt of a scan tool "Clear DTCs" command.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

 

A module which loses power during an ignition cycle will cause other module(s) to set Lost Communication DTCs.

 

A module which loses power during an ignition cycle will cause other module(s) to set Lost Communication DTCs.

 

The malfunction is due to an open in the class 2 serial data circuit or an open in the module.

 

The module which was not communicating may have set Lost Communication DTCs for those modules that it was monitoring.

 

The modules which can communicate indicate the module which cannot communicate. You must clear the DTC from these modules to avoid future misdiagnosis.

 

Step

Action

Value(s)

Yes

No

 

1

Test the battery positive voltage circuit(s) of the module that is not communicating for an open or a short to ground. Refer to Control Module References for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

 

Did you find and correct the condition?

--

Go to Step 9

Go to Step 2

 

2

Turn OFF the ignition.

Test the ground circuit(s) of the module that is not communicating for an open. Refer to Control Module References for the applicable schematic. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 3

 

3

Disconnect the scan tool.

Test the class 2 serial data circuit for continuity. Refer to Testing for Continuity in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 7

Go to Step 4

 

4

Test the class 2 serial data circuit of the module that is not communicating for an open between the module and pin 2 on the Data Link Connector (DLC). Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

 

Did you find and correct the condition?

--

Go to Step 7

Go to Step 5

 

5

Inspect for poor connections at the battery positive voltage circuit(s), the ground circuit(s) , and the class 2 serial data circuit of the module that is not communicating. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

 

Did you find and correct the condition?

--

Go to Step 7

Go to Step 6

 

6

Replace the module which is not communicating. Refer to Control Module References for the appropriate repair instructions.

 

Did you complete the replacement?

--

Go to Step 9

--

 

7

Install a scan tool

Turn ON the ignition leaving the engine OFF.

Select the Display DTCs function for the module which was not communicating.

Does the scan tool display any DTCs which do not begin with a "U"?

--

Go to Control Module References or the applicable Diagnostic System Check

Go to Step 8

 

8

Use the scan tool in order to clear the DTCs.

 

Did you complete the action?

--

Go to Step 9

--

 

9

Select the Display DTCs function for the module(s) which had the Lost Communication with xxx DTC set.

 

Does the scan tool display any DTCs which do not begin with a "U"?

--

Go to Control Module References or the applicable Diagnostic System Check

Go to Step 10

 

10

Use the scan tool in order to clear the DTCs.

Continue diagnosing or clearing the DTCs until all the modules have been diagnosed and all the DTCs have been cleared.

Did you complete the action?

--

System OK

--

 

 

 

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[roberson104]

Your other code u1041 reads same way. You might have a bad ground somewhere, possibly to the fuel pump.

[GM-Tech]

As mentioned, "U" codes are communication codes. We see these sporadically but many times they are falsely set and I have never seen one cause a driveability problem. Clear the codes and if they don't come right back, there's probably nothing wrong... at least in terms of the "U" codes.

[95Sierra2500]

I have never heard of 'u' codes, just 'p' codes from the OBDII computers, so I'm no help there. More detail is needed on your hard starting problem, you would need to check your plugs and wires, and (if you have one, I don't know about 2000's) distributor cap and rotor. From there I would also check the battery to make sure it's good, and make sure the starter is in good shape (both these can be tested at your local auto parts store). I would then check your fuel pressure, and if it's low try changing your fuel filter first. If none of this helps, then chances are it's your fuel pump and you're looking at $200 (I think) just for the pump, and if you aren't mechanically inclined even more for installation.

[JOE2003]

I have never heard of 'u' codes, just 'p' codes from the OBDII computers, so I'm no help there. More detail is needed on your hard starting problem, you would need to check your plugs and wires, and (if you have one, I don't know about 2000's) distributor cap and rotor. From there I would also check the battery to make sure it's good, and make sure the starter is in good shape (both these can be tested at your local auto parts store). I would then check your fuel pressure, and if it's low try changing your fuel filter first. If none of this helps, then chances are it's your fuel pump and you're looking at $200 (I think) just for the pump, and if you aren't mechanically inclined even more for installation.

 

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[JOE2003]

I have never heard of 'u' codes, just 'p' codes from the OBDII computers, so I'm no help there. More detail is needed on your hard starting problem, you would need to check your plugs and wires, and (if you have one, I don't know about 2000's) distributor cap and rotor. From there I would also check the battery to make sure it's good, and make sure the starter is in good shape (both these can be tested at your local auto parts store). I would then check your fuel pressure, and if it's low try changing your fuel filter first. If none of this helps, then chances are it's your fuel pump and you're looking at $200 (I think) just for the pump, and if you aren't mechanically inclined even more for installation.

 

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this is a 2000 silverado with the 5.3l the u codes are dealing with the control modules for the different options u1026 is loss of comm with atc/trans u1041 is loss of ebtcm commucation

[JOE2003]

As mentioned, "U" codes are communication codes.  We see these sporadically but many times they are falsely set and I have never seen one cause a driveability problem.  Clear the codes and if they don't come right back, there's probably nothing wrong... at least in terms of the "U" codes.

 

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THANKS FOR ALL THE HELP WITH THIS I FOUND NOTHING WRONG YET

HAVE NEW FUEL PUMP ON ORDER FOR THE STARTING PROBLEM EBAY AC DELCO PUMP FOR 126.60