Diagnostic Instructions

DTC Descriptors

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

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

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

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

1. Using the DTC Descriptor and Diagnostic Aids determine which module is not communicating.
2. Ignition OFF, disconnect the harness connector at the module that is not communicating.
3. Test for less than 0.5 ohm of resistance between each ground circuit of the module that is not communicating and ground.

⇒	If greater than 0.5 ohm, repair the open/high resistance in the ground circuit.

4. Test for battery voltage between each battery positive voltage circuit of the module that is not communicating and ground.

⇒	If less than battery voltage, repair the short to ground or open/high resistance in the battery positive voltage circuit.

5. Ignition ON, test for battery voltage between each ignition circuit of the module that is not communicating and ground.

⇒	If less than battery voltage, repair the short to ground or open/high resistance in the ignition circuit.

6. Ignition OFF, disconnect the harness connector at the module that reported the no communication DTC.
7. 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 greater than 0.5 ohm, repair the open/high resistance in the serial data circuit.

8. If all tests normal, replace the module that is not communicating.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for non-communicating module replacement, setup, and programming