U1846
DTC U1845 or U1846
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptors
DTC U1845 00
-
Drive Motor Control Module 1 Lost Communication with Hybrid Powertrain Control Module
Circuit/System Description
The motor control module and the hybrid powertrain control module are all internal to the starter/generator control module. The hybrid powertrain control module sends out diagnostic trouble code information to other control modules regarding the motor control module. All circuits to the hybrid powertrain control module and motor control module are also internal to the starter/generator control module and replaced as a single component.
Communication diagnostics for the serial data, including control module power and ground as well as the wakeup circuits for motor control module and the hybrid powertrain control module are all diagnosed from external sources only to the starter/generator control module connector because any circuit fault condition within the starter/generator control module will cause a complete replacement.
Conditions for Running the DTC
* The system voltage is greater than 9.5 V.
* The vehicle power mode master requires serial data communication to occur from this specific control module.
Conditions for Setting the DTC
A supervised periodic message that includes the transmitter module availability has not been received for more than 500 ms.
Action Taken When the DTC Sets
The DTC U1845 is a type B DTC.
Conditions for Clearing the DTC
The DTC U1845 is a type B DTC.
Diagnostic Aids
* Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios:
- A control module on the data communication circuit was disconnected while the communication circuit is awake.
- Power to one or more control modules was interrupted during diagnosis.
- A low battery condition was present, so some control modules stop communicating when battery voltage drops below a certain threshold.
- Battery power was restored to the vehicle and control modules on the communication circuit did not all re-initialize at the same time.
- If a loss-of-communication U-code appears in history for no apparent reason, it is most likely associated with one of the scenarios above. These are all temporary conditions and should never be interpreted as an intermittent fault, causing you to replace a part.
* A control module may have a U-code stored in history that does not require any repairs. Issues with late or corrupted messages between control modules can be temporary with no apparent symptom or complaint; this does not mean the control module is faulty. Do not replace a control module based only on a history U-code.
* The control module may not have internal protection for specific control circuits and may open a B+ or ignition fuse. If a fuse is open and the B+ or ignition circuit is not shorted to ground, ensure none of the control circuits are shorted to ground before replacing the non communicating control module.
* If DTC U1845 is only set current in the hybrid powertrain control module, the starter/generator control module must be replaced due to all circuits between the hybrid powertrain control module and motor control module being internal to the starter/generator control module.
Reference Information
Schematic Reference
* Data Communication Schematics [1][2]Electrical Diagrams
* Control Module References Programming and Relearning
Connector End View Reference
Component Connector End Views Connector End Views By Name
Description and Operation
Data Link Communications Description and Operation Description and Operation
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Programming and Relearning for scan tool information
Circuit/System Verification
Danger:
The eAssist battery pack assembly will utilize an exchange program. Please consult the most recent revision of bulletin/PI# PIC5520, available in Service Information♦(SI), for a list of approved eAssist battery pack assembly service procedures. Components that may be removed and serviced without exchanging the complete battery pack assembly are identified in the bulletin/PI. Please contact the GM Technical Assistance Center (1-877-446-8227) if you have any questions.
1. Verify that DTC U0293 is not set.
• If the DTC is set, refer to DTC U0100-U02FF (without HP6) U0100DTC U0100-U02FF (with HP6) .
2. Verify that DTC U1845 is not set current only in the K114 hybrid powertrain control module.
• If the DTC is set current in the K114 hybrid powertrain control module only, replace the K59 starter/generator control module.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* GMLAN Wiring Repairs GMLAN Wiring Repairs
* Control Module References Programming and Relearning for control module replacement, programming and setup