U1000 class 2

Google it,

Make sure battery has a full charge and battery connections all good. Check fusible links where applicable. Any component that doesn't work and is fuse protected, not only check the fuse, check the fuse circuit for voltage, use a test lite.
The wiring diagram is for starter circuit, you can see the fuses. Any testing for starter motor, make sure tranny is in park or neutral and parking brake is set. It is possible to jump crank relay to see if starter motor will crank, but, that doesn't mean it will start. Make sure vehicle can't move.

Did you check for BCM codes
DTC B1477
Retained Accessory Power Circuit Low
DTC B1478
Retained Accessory Power Circuit High
DTC B1397
Device Voltage Reference Out #1 CKT Low
DTC B1398
Device Voltage Reference Out #1 CKT High
Charging system check ?

Diagnostic System Check - Retained Accessory Power
Test Description
The numbers below refer to the step numbers on the diagnostic table.

1. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.


2. This step is checking for DTCs in the BCM.


3. This step is checking for RAP specific DTCs.

Step

Action

Yes

No

1

Install a scan tool.

Does the scan tool power up?
Go to Step 2
Go to Scan Tool Does Not Power Up in Data Link Communications

2

1. Turn ON the ignition, with the engine OFF.
2. Attempt to establish communication with the body control module.

Does the scan tool communicate with the BCM?
Go to Step 3
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

3

Important: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.

1. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
2. Rotate the ignition switch through all positions while observing the Class 2 Power Mode on the Scan Tool. Refer to the Serial Data Power Mode table within the Body Control System Description and Operation in Body Control Systems, for a list of the power mode states that correspond to each ignition switch position.

Does the Class 2 Power Mode parameter reading match the ignition switch position for all the selected positions?
Go to Step 4
Go to Power Mode Mismatch in Body Control System

4

Select the BCM display DTCs function on the scan tool.

Does the scan tool display any DTCs?
Go to Step 5
Go to the Symptoms list in the appropriate service category

5

Does the scan tool display B1477 or B1478?
Go to Diagnostic Trouble Code (DTC) List
Go to Symptoms - Retained Accessory Power

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

Is check engine light Lit ? You should have all the computers on the vehicle check for DTC'S - diagnostic trouble codes ! Check the battery an all connections !
Diagnostic Starting Point - Engine Electrical
Begin the system diagnosis with the Diagnostic System Check - Engine Electrical . The Diagnostic System Check will provide the following information:
?€¢
The identification of the control module(s) which command the system.

?€¢
The ability of the control modules to communicate through the serial data circuit.

?€¢
The identification of any stored diagnostic trouble codes (DTCs) and their status.

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.
Diagnostic System Check - Engine Electrical
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
The symptom list in Symptoms will determine the correct diagnostic procedure to use.
The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
Step
Action
Yes
No

1
Did you perform the Battery Inspection/Test?
Go to Step 2
Go to Battery Inspection/Test

2
Install a scan tool.
Does the scan tool power up?
Go to Step 4
Go to Scan Tool Does Not Power Up in Data Link Communications

3
Important: The engine may start during the following step. Turn OFF the engine as soon as you have observed the Crank power mode.
Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool.
Rotate the ignition switch through all positions while observing the Class 2 Power Mode on the Scan Tool. Refer to the Serial Data Power Mode table within the Body Control System Description and Operation in Body Control System for a list of the power mode states that correspond to each ignition switch position.
Does the Class 2 Power Mode parameter reading match the ignition switch position for all the selected positions?
Go to Step 4
Go to Power Mode Mismatch in Body Control System

4
Turn ON the ignition, with the engine OFF.
Attempt to communicate with each module on the class 2 serial data circuit:
• The body control module (BCM)
• The driver information center (DIC)
• The instrument panel cluster (IPC)
• The powertrain control module (PCM)
Does the scan tool communicate with any module on the class 2 serial data circuit?
Go to Step 5
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

5
Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set.
Record all of the displayed DTCs the DTC status and the module which set the DTC.
Does the scan tool display any DTCs?
Go to Step 6
Go to Symptoms - Engine Electrical

6
Does the scan tool display any DTC beginning with "U"?
Go to Diagnostic Trouble Code (DTC) List in Data Link Communications
Go to Step 7

7
Does the scan tool display any DTC beginning with "B"?
Go to Diagnostic Trouble Code (DTC) List in Body Control Systems
Go to Diagnostic Trouble Code (DTC)

This is the way you start diagnosing this system !
Automatic Level Control Diagnostic System Check
Install a scan tool. Does the scan tool power up?
Go to Step 2
Go to Scan Tool Does Not Power Up in Data Link Communications

2

1. Turn ON the ignition, with the engine OFF.
2. Attempt to establish communication with the Rear Integrated Module (RIM).

Does the scan tool communicate with the RIM?
Go to Step 3
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications
Select the automatic level control display DTC function on the scan tool.
Does the scan tool display any DTCs?
Go to Step 4
Go to Symptoms

4
Does the scan tool display any DTCs which begin with a "U"?
Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Connector Diagnosis
Go to Step 5

5

Does the scan tool display DTC B1007 or B1009?
Go to Diagnostic Trouble Code (DTC) List/Type in Body Control System
Go to Step 6

6

Does the scan tool display DTC B1327?
Go to Diagnostic Trouble Code (DTC) List/Type in Engine Electrical
Go to Diagnostic Trouble Code (DTC) List/Type
This is one you should take to a ASE certified repair facility , there are electronic modules involved you have no idea about !

What pins did your friend jump in the DLC ,2 an 4 ? they don't call it ALDL any more ! Does the vehicle start an run ?
The data link connector (DLC) is a standardized 16 cavity connector. Connector design and location is dictated by an industry wide standard, and is required to provide the following:
?€¢
Scan tool power battery positive voltage at terminal 16.

?€¢
Scan tool power ground at terminal 4.

?€¢
Common signal ground at terminal 5.

?€¢
Class 2 signal at terminal 2.

I wonder how many friends out there mess up other friends vehicles from stuff they see on the internet . When are you people going to learn , your messing with complex electronics !!!!! He shorted out the class 2 serial data communication network !
Do you know what this is ? if not you need to take to your local GM Mr. goodwrench !
Class 2 Serial Data Link
The data link is configured as a ring with discrete lines entering and leaving each module. This allows communications to the modules on the ring if one of the two discrete circuits is open.
A total list of the control modules on the Class 2 Serial Data Line can include the following:
?€¢
Dash Integration Module (DIM)

?€¢
Driver Door Module (DDM)

?€¢
Electronic Brake Control Module (EBCM)

?€¢
Head Up Display (HUD) w/UV6

?€¢
HVAC Control Module w/C67

?€¢
Inflatable Restraint Sensing and Diagnostic Module (SDM)

?€¢
Instrument Panel Cluster (IPC)

?€¢
Instrument Panel Integration Module (IPM) w/CJ2

?€¢
Memory Seat Module (MSM) w/A45

?€¢
Powertrain Control Module (PCM)

?€¢
Radio

?€¢
Rear Integration Module (RIM)

?€¢
Remote Control Door Lock Receiver (RCDLR)

?€¢
Remote Playback Device - CD Changer w/U1S

?€¢
Theft Deterrent Control Module

?€¢
Vehicle Interface Unit (VIU) w/UE1

Power door serial data does not communicate with the scan tool via the DLC. Power door serial data information is interpreted by the driver door module (DDM) and transmitted on the Class 2 data link by the DDM.
Power door serial data is used for serial data communication between the four door modules as well as the driver door switch assembly (DDSA
Scan Tool Does Not Communicate with Class 2 Device
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. Connecting a scan tool to the DLC allows communication with the modules for diagnostic purposes.
The engine will not start when there is a total malfunction of the class 2 serial data circuit while the engine is not running.
Test Description
The numbers below refer to the step numbers on the diagnostic table.

1. A partial malfunction in the class 2 serial data circuit uses a different procedure from a total malfunction of the class 2 serial data circuit.


2. The DTC U1300, U1301, and U1305 may be retrieved with a history status. These DTCs are not the cause of the present condition.


3. A State of Health DTC with a history status may be present along with a U1000 or a U1255 with a current status. This indicates that the malfunction occurred when the ignition was on.

Hey John ! how's it going ? How do you know you have a class 2 data bus problem ? Need some more info ! Do you have a scan tool ? Can't communicate with the PCM ? Have a check engine light on ?
You may access 2 data lines with the scan tool. The serial data line UART (circuit 800) allows the following components to communicate via serial data:
?€¢
The scan tool

?€¢
The powertrain control module (PCM)

?€¢
The instrument panel cluster

?€¢
The sensing diagnostic module (SDM)

?€¢
The electronic brake control module (EBCM)

The serial data line class 2 (circuit 1807) allows the scan tool to access directly the PCM in order to read emissions-related information. The scan tool gains access to both data lines through the data link connector (DLC). You may then monitor or control system operations for diagnostic purposes.

U codes pertain to the class 2 serial data network . A dead module ,a short on the network will bring down the network - no communications between modules = no start problems .
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. 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 identification number with at least one critical parameter within 5 seconds of beginning serial data communication, DTC U1000 or U1255 DTC is set. When more than one critical parameter does not have an identification number associated with it, the DTC will only be reported once. The class 2 serial data line on this vehicle is a star configuration. The following modules communicate on the class 2 serial data line:
• The body control module (BCM)
• The electronic brake control module (EBCM)
• The inflatable restraint sensing and diagnostic module (SDM)
• The instrument panel cluster (IPC)
• The powertrain control module (PCM)
• The radio
• The remote control door lock receiver (RCDLR)
• The vehicle communication interface module (VCIM)

Look's like a communication problem with the PCM & EBCM !
Powertrain Control Module (PCM)
U1016
Electronic Brake Control Module (EBCM)
U1041
Diagnostic Aids
• An intermittent open between a module and a star connector may cause this DTC to set.
• A poor connection at a module or a star connector may cause this DTC to set.
• An intermittent open in a star connector may cause this DTC to set.
• An open voltage or ground circuit to a module may cause this DTC to set.
• An internal module malfunction may cause this DTC to set.


012 GM Class II Communications

The protocol is class 2 . Maybe your code reader is no good .
012 GM Class II Communications

Data Link Connector (DLC)
The data link connector (DLC) contains the following serial data links:
• Class II
• Entertainment and Comfort (E&C)
The DLC also provides a power source for the scan tool as follows:
• Unswitched voltage (B+) at DLC terminal 16 (circuit 1450)
• Ground at terminal 4 (circuit 1450) and terminal 5 (circuit 1550)

Class II Serial Data Link
The class II serial data link allows the following modules to communicate data with each other:
• Body control module (BCM)
• Electronic brake traction control module (EBTCM)
• Heater-A/C control (if equipped with RPO CJ2)
• Instrument panel cluster (IPC)
• Powertrain control module (PCM)
• Inflatable Restraint Sensing and Diagnostic Module (SDM).
The Class II serial data link allows a Scan Tool scan tool to communicate with the above modules for diagnostic and testing purposes. The Class II serial data link is located at the DLC connector terminal 2. Terminal 2 consists of the following circuits:
• Circuit 1036
• Circuit 1037
• Circuit 1128
• Circuit 1049
• Circuit 1122
• Circuit 1132
Entertainment and Comfort (E&C) Serial Data Link
The entertainment and comfort (E&C) serial data link allows a scan tool to communicate with the radio or the mobile telephone handset the remote CD player (if equipped). This communication is for diagnostic and testing purposes. The E&C serial data link is located at the DLC connector terminal 14, circuit 835.
PIN #9 goes to the air bag module .