Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.
Control Module References (See: Testing and Inspection/Programming and Relearning) for module replacement, setup, and programming
U1815
DTC U1815
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic System
Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Strategy Based Diagnosis) for an
overview of the diagnostic approach.
* Diagnostic Procedure Instructions (See: Testing and Inspection/Initial Inspection and Diagnostic Overview/Diagnostic Procedure
Instructions) provides an overview of each diagnostic category.
DTC Descriptor
DTC U1815 00
- Lost Communication With Drive Motor Control Module "A" on Bus "B"
Diagnostic Fault Information
Circuit/System Description
Modules connected to the high speed hybrid GMLAN serial data circuits monitor for serial data communications during normal vehicle operation.
Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are
needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are
used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the
transmitter module.
The communication enable and the wakeup circuits are energized by a specific module to activate another specific module when the ignition key is
in ACC, ON or START. Only the modules using high speed GMLAN serial data are connected to the enable or wakeup circuits. Refer to the
schematics to determine which modules activate and are activated using the enable or wakeup circuits.
The motor control module (MCM) 1, 2, and the hybrid powertrain control module (HPCM) are all internal to the drive motor power inverter
module (PIM). The MCMs communicate only with the HPCM with the HPCM sending out DTC information to other modules regarding the
MCMs. All circuits to the MCM are also internal to the PIM and is replaced as a single component.
Communication diagnostics for the serial data, including module power and ground as well as the wakeup circuits for both MCMs, and the HPCM
are all diagnosed from external sources only to the PIM connector because any circuit fault condition within the PIM will cause a complete
replacement.
Conditions for Running the DTC
* The system voltage is between 9-16 volts.
* The vehicle power mode master requires serial data communication to occur from this specific module.
Conditions for Setting the DTC
A supervised periodic message that includes the transmitter module availability has not been received.
Action Taken When the DTC Sets
The modules is never signaled, therefore the specific subsystems will not function.
