2010 Cadillac Truck Escalade EXT AWD V8-6.2L Page 2984
normal, replace the serial data gateway module.
6. If all circuits test normal, replace the accessory DC power control module.
PIM
1. Ignition OFF, disconnect harness connector X1 of the drive motor generator power inverter module (PIM).
2. Ignition ON, verify that a test lamp illuminates between each B+ circuit and ground.
瀚慖f the test lamp does not illuminate, test each B+ circuit for an open/high resistance. If the circuit fuse is open, test the control circuits of
the PIM for a short to ground.
3. Verify that a test lamp illuminates between the ignition circuit terminal 20 and ground.
瀚慖f the test lamp does not illuminate, test the ignition circuit for an open/high resistance. If the circuit fuse is open, test the control circuits
of the PIM for a short to ground.
4. Verify that a test lamp illuminates between the wake up signal circuit terminal 19 and ground.
瀚慖f the test lamp does not illuminate, test the wake up signal circuit for an open/high resistance or a short to ground. If the circuit tests
normal, replace the serial data gateway module.
5. If all circuits test normal, replace the drive motor generator power inverter module.
Repair Instructions
Perform the Diagnostic Repair Verification (See: Verification Tests) after completing the diagnostic procedure.
* GMLAN Wiring Repairs (See: Testing and Inspection/Component Tests and General Diagnostics/General Electrical Diagnostic
Procedures/Wiring Repairs/GMLAN Wiring Repairs)
* Control Module References (See: Testing and Inspection/Programming and Relearning) for control module replacement, setup, and
programming
U1842
DTC U1842
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 U1842
- Lost Communication With ECM/PCM
Circuit/System Description
Modules connected to the 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.
Conditions for Running the DTCs
* The system voltage is between 9-16 volts.
* The vehicle power mode master indicates that the need for serial data communications.
Conditions for Setting the DTC
A supervised periodic message that includes the transmitter module availability has not been received.
Action Taken When the DTCs Sets
The modules is never signaled, therefore the specific subsystems will not function.
