DTC Descriptor
DTC U0100: Lost Communication With Engine/Powertrain Control Module (ECM/PCM)DTC U0101: Lost Communication With Transmission Control Module (TCM)
DTC U0106: Lost Communication With Glow Plug Control Module (GPCM)
DTC U0166: Lost Communication With Auxiliary Heater Control Module (FOH) (Coolant Heater)
Diagnostic Fault Information
Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
High speed GMLAN serial data bus (+) | U0073 | U0100, U0101, U0106, U0166 | U0073 | -- |
High speed GMLAN serial data bus (-) | U0073 | U0100, U0101, U0106, U0166 | U0073 | -- |
Circuit/System Description
Modules connected to the high and low speed 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 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 DTC
| • | The system voltage is between 9-16 volts. |
| • | The vehicle power mode requires serial data communications. |
| • | The DTC U0073 is not set as current. |
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 module setting the DTC uses default values for the missing parameters.
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 of 50, without a repeat of the malfunction. |
Diagnostic Aids
Use the DTC Descriptor list to determine the module which is not communicating. If there are multiple non-communicating modules in series on high speed GMLAN, choose the one closest to the data link connector (DLC) for this diagnostic.
Reference Information
Schematic Reference
Connector End View Reference
Master Electrical Component List
Electrical Information Reference
Circuit/System Testing
- Using the DTC Descriptor and Diagnostic Aids determine which module is not communicating.
- Ignition OFF, disconnect the harness connector at the module that is not communicating.
- Test for less than 0.5 ohm of resistance between each ground circuit of the module that is not communicating and ground.
- Test for battery voltage between each battery positive voltage circuit of the module that is not communicating and ground.
- Ignition ON, test for battery voltage between each ignition circuit of the module that is not communicating and ground.
- Ignition OFF, disconnect the harness connector at the module that reported the no communication DTC.
- Ignition OFF, test for less than 0.5 ohm of resistance in each serial data circuit between the module that is not communicating and the module that reported the DTC.
- If all tests normal, replace the module that is not communicating.
| ⇒ | If greater than 0.5 ohm, repair the open/high resistance in the ground circuit. |
| ⇒ | If less than battery voltage, repair the short to ground or open/high resistance in the battery positive voltage circuit. |
| ⇒ | If less than battery voltage, repair the short to ground or open/high resistance in the ignition circuit. |
| ⇒ | If greater than 0.5 ohm, repair the open/high resistance in the serial data circuit. |
Repair Instructions
Important: Always perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for non-communicating module replacement, setup, and programming.
