Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptors
DTC U0100 00: Lost Communication With Engine/Powertrain Control Module (ECM/PCM)DTC U0101 00: Lost Communication With Transmission Control Module (TCM)
DTC U0104 00: Lost Communication With Cruise Control Module
DTC U0121 00: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U0122 00: Lost Communication With Vehicle Dynamics Control Module
DTC U0132 00: Lost Communication With Ride Level Control Module
DTC U0140 00: Lost Communication With Body Control Module (BCM)
DTC U0151 00: Lost Communication With Sensing and Diagnostic Module (SDM)
DTC U0155 00: Lost Communication With Instrument Panel Cluster (IPC) Control Module
DTC U0184 00: Lost Communication With Radio
DTC U0199 00: Lost Communication With Door control Module A
DTC U0200 00: Lost Communication With Door control Module B
DTC U2105 00: Lost Communication With Engine Control Module (ECM)
DTC U2106 00: Lost Communication With Transmission Control Module (TCM)
DTC U2107 00: Lost Communication With Body Control Module (BCM)
DTC U2108 00: Lost Communication With Electronic Brake Control Module (EBCM)
DTC U2112 00: Lost Communication With Electronic Suspension Control (ESC) Module
DTC U2113 00: Lost Communication With Sensing and Diagnostic Module (SDM)
DTC U2116 00: Lost Communication With Instrument Panel Cluster (IPC)
DTC U2118 00: Lost Communication With Head Up Display (HUD)
DTC U2120 00: Lost Communication With Dynamic Headlamp Leveling (DHL) Device
DTC U2122 00: Lost Communication With Radio
DTC U2124 00: Lost Communication With Audio Amplifier
DTC U2125 00: Lost Communication With Communication Interface Module (OnStar)
DTC U2127 00: Lost Communication With HVAC
DTC U2130 00: Lost Communication With Driver Door Module (DDM)
DTC U2132 00: Lost Communication With Passenger Door Module (PDM)
DTC U2135 00: Lost Communication With Rear Integration Module (RIM)
DTC U2138 00: Lost Communication With Steering Column Lock Control Module (SCLCM)
DTC U2144 00: Lost Communication With Distance Sensing Cruise Control (DSCC) Module
DTC U2162 00: Lost Communication With Instrument Panel Integration Module (IPM)
DTC U2163 00: Lost Communication With Left Rear Door Module (LRDM)
DTC U2164 00: Lost Communication With Right Rear Door Module (RRDM)
DTC U2165 00: Lost Communication With Driver Door Switch (DDS)
DTC U2166 00: Lost Communication With Driver Position Module (DPM)
DTC U2167 00: Lost Communication With Remote Control Door Lock Receiver (RCDLR)
DTC U2172 00: Lost Communication With Digital Radio Receiver (DRR)
DTC U2179 00: Lost Communication With Television Module
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Low speed GMLAN serial data | 1 | U0100-U0299 | 1 | -- |
Battery positive voltage circuits | U0100-U0299 | U0100-U0299 | -- | -- |
Ignition voltage circuits | U0100-U0299 | U0100-U0299 | -- | -- |
Module ground circuits | U0100-U0299 | U0100-U0299 | -- | -- |
Accessory Wake Up Serial Data | U1814 | U0100-U0299 | -- | -- |
High Speed GMLAN Serial Data Wake Up | U2099 | U0100-U0299 | -- | -- |
1. Scan Tool Does Not Communicate with Low Speed GMLAN Device | ||||
Circuit/System Description
The data link connector (DLC) allows a scan tool to communicate with the high speed GMLAN serial data circuit. The serial data is transmitted on 2 twisted wires that allow speed up to 500 Kbps. The twisted pair is terminated with two 120 ohms resistors, one is internal to the engine control module (ECM) and the other is internal to the instrument panel module (IPM). The resistors are used to reduce noise on the high speed GMLAN bus during normal vehicle operation. The high speed GMLAN is a differential bus. The high speed GMLAN serial data bus (+) and high speed GMLAN serial data (-) are driven to opposite extremes from a rest or idle level. The idle level which is approximately 2.5 volts is considered a recessive transmitted data and is interpreted as a logic 1. Driving the lines to their extremes adds 1 volt to high speed GMLAN serial data bus (+) and subtracts 1 volt from high speed GMLAN serial data bus (-) wire. This dominant state is interpreted as a logic 0.
Two different outputs are used by IPM to activate the high speed GMLAN bus:
| • | Accessory wake up, active in all power modes when IPM is awake except Crank and in a remote start request. |
| • | High speed communication enable, active in all power modes when IPM is awake and in a remote start request. |
The accessory wake up signal wakes up the ECM and the transmission control module (TCM) only. This output is disabled in Crank power mode for internal fail enable of the ECM and TCM. The high speed communication enable signal wakes up all the other modules on the high speed GMLAN bus.
Conditions for Running the DTC
| • | The system voltage is between 9-16 volts. |
| • | The vehicle power mode requires serial data communication to occur. |
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 uses a default value 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 above to determine the module which is not communicating. |
| • | If there are multiple non-communicating modules choose the one closest to the data link connector (DLC). |
| • | Use Data Link References to determine if the module uses high or low speed GMLAN serial data communications |
| • | Some modules may not have internal protection for specific voltage outputs and may open a battery positive voltage or ignition voltage source fuse. If a voltage input fuse is open and no short is found in that circuit, ensure that no module output voltage circuit is shorted to ground before replacing the module. |
| • | This diagnostic can be used for any module that should communicate with high or low speed GMLAN serial data providing the vehicle is equipped with the option that uses that module. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Scan Tool References
Data Link Communications Description and Operation for Scan Tool information.
Circuit/System Testing
- Using the DTC Descriptor and Diagnostic Aids above, determine the module that is not communicating that should be tested.
- Ignition OFF, disconnect the harness connector of the module that is not communicating.
- Ignition ON, verify that a test lamp illuminates between the high speed GMLAN serial data wake up circuit OR the accessory wake up serial data circuit and ground.
- Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
- Verify that a test lamp illuminates between all ignition voltage circuits and ground.
- Test for less than 1 ohm of resistance between the module ground circuits and ground.
- Test for less than 1 ohm of resistance in the GMLAN serial data circuit(s) between the non-communicating module and the module that displays the DTC.
- If all circuits test normal, replace the module that is not communicating.
Important: If more than one module is not communicating use Data Communication Schematics to determine which module is closest to the DLC. Start diagnostics with that module.
Important: Only the high speed GMLAN modules have a wired serial data wake up circuit. Refer to the module schematics to identify which modules have a wake up circuit. If the module that is not communicating does not have a serial data wake up circuit, proceed to step 4.
| ⇒ | If the test lamp does not illuminate, test the circuit for an open/high resistance. If the circuits test normal, replace the BCM. |
| ⇒ | If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module. |
| ⇒ | If the test lamp does not illuminate, test the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace the faulty module. |
| ⇒ | If greater than 1 ohm, test the ground circuit for an open. |
| ⇒ | If greater than 1 ohm of resistance, test the GMLAN serial data circuit(s) for open/high resistance. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for module replacement, setup, and programming |
