Diagnostic Instructions
DTC Descriptor
DTC U1843: 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.
Conditions for Clearing the DTC
| • | A current DTC clears when the malfunction is no longer present. |
| • | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction. |
Circuit/System Verification
Verify that U0100 is not set.
