How do you fix a u1000 class 2 communication malfunction code

U1064 = Loss of Communications with DIM.
U1000 = Class 2 Communication Malfunction.
This sounds like the electronics somewhere in the system is struggling to communicate with the main ECU, ( the car's brain), so it's gone into a safe mode to protect the car. Something has been disconnected when the work was done and the electronics either can't find it or doesn't recognise it when it was reconnected.
You'll probably need good auto electrician to help you fix this issue.

Google it,

When a malfunction such as an open fuse to a module occurs while modules are communicating, a DTC U1001-1254 Loss of 000 Communications is set current. When the modules stop communicating the current DTC U1001-1254 Loss of 000 Communications is cleared but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules so U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 or U1255 is set. Radio quit working shows Code IRC U1000 please help

DTC U1000 and U1255
Class 2 Communication Malfunction , Do you know what class 2 serial data communication network is ? What module set this code an what kind of scan tool did you use to read this code .
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 ID 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. When a module does not associate an ID number with at least one critical parameter within about 5.5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. When more than one critical parameter does not have an ID number associated with it, the DTC will only be reported once.
The table below list the modules on the Class 2 Serial Data Circuit that will set a U1000 or U1255 and should be actively communicating the previously described messages on the Class 2 Serial Data Circuit.

Control Module

ID Number
Body Control Module (BCM)
064
Electronic Brake Control Module (EBCM)
040
Instrument Panel Cluster (IPC)
096
Radio
128
Powertrain Control Module (PCM)
016
Sensing and Diagnostic Module (SDM)
088
Diagnostic Aids
When a malfunction such as a open fuse to a module occurs while modules are communicating, a Loss of Communication DTC is set as current. When the modules stop communicating, ignition is turned off, the current Loss Communication DTC is cleared but the history DTC remains. When the modules begin to communicate again, the ignition is turned on, the module with the open fuse will not be learned by the other modules so U1000 or U1255 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only U1000 or U1255 is set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.

1. A DTC U1001 - U1254 Lost Communications with with a history status may indicate the cause of U1000 or U1255.


2. The modules not communicating are the likely cause of U1000 or U1255. The modules that are available on the class 2 serial data circuit are listed in the Circuit Description.


3. The module which was not communicating due to a poor connection to the class 2 serial data circuit may have set DTC U1001 - U1254 Lost Communications with for those modules that it was monitoring.


4. The modules which can communicate indicate the module which cannot communicate. You must clear the serial data communication DTCs from these modules to avoid future misdiagnosis.


5. If all modules are communicating, the module which set U1000 or U1255 may have done so due to some other condition.


6. The module which set U1000 or U1255 is the likely cause of the malfunction.

1

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Record the DTCs set in each module. If using a Tech 2, use the Class 2 DTC Check feature to determine which modules have DTCs set.

Did you record any DTCs in the range of U1001-U1254 with a history status?
Go to Diagnostic Trouble Code (DTC) List
Go to Step 2

2

1. Turn ON the ignition, with the engine OFF.
2. Attempt to communicate with each module on the class 2 serial data circuit. If using a Tech 2, obtain this information using the class 2 Message Monitor feature.
3. Record all of the modules communicating on the class 2 serial data circuit.
4. Compare the list of modules which are communicating to the list given in Circuit Description.

Does any module on the class 2 serial data circuit not communicate?
YES - Go to Step 3
NO - Go to Step 12
Test the following circuits of the module that is not communicating for an open or short to ground:
?€¢
The battery positive voltage supply circuits

?€¢
The switched battery positive supply circuits

?€¢
The battery positive voltage output circuits

?€¢
The ignition voltage input circuits

?€¢
The ignition voltage output circuits

Refer to the following:
?€¢
Control Module References in Body Control System for the applicable schematic

?€¢
Circuit Testing in Wiring Systems

?€¢
Wiring Repairs in Wiring Systems

Did you find and correct the condition?

5

Important: Inspect all connectors in the serial data communications circuit.
Refer to the following:
?€¢
Data Link Connector Schematics

?€¢
Testing for Intermittent Conditions and Poor Connections in Wiring Systems

?€¢
Connector Repairs in Wiring Systems

1. Turn OFF the ignition.
2. Test the class 2 serial data circuits of the module that is not communicating for an open. Refer to the following:

?€¢
Data Link Connector Schematics

?€¢
Circuit Testing in Wiring Systems

?€¢
Wiring Repairs in Wiring Systems

Did you find and correct the condition?
Go to Step 8
Go to Step 6

6
Inspect the harness connector of the module that is not communicating for poor connections and terminal tension at the following circuits:
?€¢
The battery positive voltage input circuits

?€¢
The switched battery positive voltage supply

?€¢
The battery positive voltage output circuits

?€¢
The ignition voltage input circuits

?€¢
The ignition voltage output circuits

?€¢
The ground circuits

?€¢
The class 2 serial data circuits

Refer to the following:
?€¢
Control Module References in Body Control System for the applicable schematic

?€¢
Testing for Intermittent Conditions and Poor Connections in Wiring Systems

?€¢
Connector Repairs in Wiring Systems

Did you find and correct the condition?
Go to Step 8
Go to Step 7

7

Important: Perform the module programming or setup procedure if required.
Replace the module that is not communicating. Refer to Control Module References in Body Control System for the appropriate Repair Instructions for the module replacement.
Did you complete the replacement?
Go to Step 10
--

8

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. 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 in Body Control System for applicable Diagnostic System Check
Go to Step 9

9
Use the scan tool in order to clear the DTCs.
Did you complete the action?
Go to Step 10
--

10

Select the Display DTCs function for the modules which had U1000 or U1255 set as a current DTC.
Does the scan tool display DTCs which do not begin with a "U"?
Go to Control Module References in Body Control System for applicable Diagnostic System Check
Go to Step 11

11

Use the scan tool in order to clear the DTCs.
Did you complete the action?
System OK
--

12
Did you record any other DTCs for the modules which had U1000 or U1255 set as a current DTC?
Go to Control Module References in Body Control System for applicable Diagnostic System Check
Go to Step 13

13

1. Install a scan tool.
2. Turn ON the ignition, with the engine OFF.
3. Use the scan tool in order to clear the DTCs.
4. Turn OFF the ignition for at least 5 seconds.
5. Turn ON the ignition with the engine OFF.
6. Select the Display DTCs function.

Does the scan tool display U1000 or U1255 set as a current DTC?
Go to Step 14
Go to Diagnostic Aids

14
Important: Perform the module programming or setup procedure if required.
Replace the module which had U1000 or U1255 set as a current DTC. Refer to Control Module References in Body Control System for the appropriate Repair Instructions for the module replacement.
Did you complete the replacement?
System OK

That is a communication bus problem code . Are you familiar with GM class 2 serial data communication network ? All the modules on the vehicle share information an they do it by the class 2 data bus.


2 UART Class 2 Bus Configuration

you need obd scanner to reset and see if comes back- if it does come back with code , post again

P0730: Incorrect Gear Ratio
U1000: Class 2 Communication Malfunction

Diagnostic Test Code (DTC) U1000 has a generic description of "Class 2 Serial Data Link Malfunction".
DTC U1064 has a description of "Loss Of Communication With Body Control Module (BCM)"
These codes can be caused by a malfunctioning charging system and should be ignored for now.

DTC P0562 has a description of "System Voltage Low". So this code basicly is only verifying that you indeed have a no-charging problem and that the other codes are most likely also caused by low system voltage.

Although these codes do verify that you have a charging system problem, they are useless in finding out exactly what is wrong with your charging system.

You will need a scan tool that is capable of 2-way communications with the PCM and performing system tests. you will also need a digital multimeter to test the system as you command the generator circuits on with the scanner. If your scanner can do this, let me know and I will get you the troubleshooting instructions for your vehicle. Otherwise, you will have to take it to someone who is properly equipped to diagnose your charging system.

it is a communication error with the ecm from the ignition switch here is the code description

GM Number U1000

Type Network - Manufacturer Controlled DTC - Manufacturer Controlled

Description Class 2 Communication Malfunction Conditions
Cause
DTC B1327, U1300, U1301 and U1305 not current (any particular device on the Class 2 serial data circuit will support some subset of these codes), the ignition switch position requires serial data communication to occur, then at least one operating parameter has not been associated with an identification number within 5 seconds after beginning serial data communication (a default value is used)