Circuit Description
Modules connected to the high speed GMLAN serial data circuits monitor each other for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have pre-recorded information about what messages are needed to be exchanged on the serial data circuits, for each have pre-recorded 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. The supervision time-out period is 250 ms.
GMLAN serial data messages contain the identification number of the transmitter module which, in the case of the engine ECU, is '100'. When a message that indicates the availability of the transmitter module is not received by (in this case) the TCM, that can communicate, sets a DTC U0100, indicating that it is the Engine ECU that cannot communicate. U0100 is a type 'B' DTC.
Conditions for Running the DTC
| • | Voltage supplied to the modules is in the normal operating voltage range of 8-18 volts. |
| • | No ECU engine speed, torque, throttle position and wheel speed sensor messages have been received for 50 milliseconds or more. |
| AND |
| • | No ECU general status message, nor engine coolant temperature and barometric readings have been received for 2 seconds of more. |
Conditions for Setting the DTC
A valid ECU message on the GMLAN has not been received for 2 seconds.
Action Taken When the DTC Sets
| • | The TCM requests the powertrain interface module (PIM) to illuminate the Check Powertrain Malfunction Indicator Lamp (MIL) in the instrument cluster during the second consecutive drive trip in which the 'Conditions for Setting the DTC' are met. |
| • | At the time of the first failure, the TCM records the operating conditions when the 'Conditions for Setting the DTC' have been met. The TCM stores this information as a failure record. |
| • | At the time of the second failure, the ECM records the operating conditions when the 'Conditions for Setting the DTC' have been met. The ECM stores this information as a freeze frame. |
| • | The TCM freezes the transmission adaptive learning function. |
| • | The TCM turns off the pressure control solenoid (causing maximum line pressure). |
| • | The TCM stores DTC 1826 into TCM history during the second consecutive trip in which the 'Conditions for Setting the DTC' are met. |
Conditions for Clearing the MIL/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. |
Diagnostic Aids
| • | A poor connection at the inoperative module may case this code to set. |
| • | An improperly powered module may cause this code to set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This DTC sets when a communication fault exists between the engine control module (ECM) and the TCM. Check for DTCs U0001 or U0101. If any of these DTCs are present, diagnose them first.
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If a module is not awake, the modules expecting to receive data cannot detect the presence of the transmitting module.
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The TCM needs time to reset memory.
Step | Action | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Automatic Transmission Controls Schematics For information on testing wiring faults, refer to Wiring Systems. | |||||||||||
1 | Has the Diagnostic System Check - Automatic Transmission been completed? | Go to Step 2 | |||||||||
Does the Tech 2 indicate that DTCs U0001 or U0101 are either current or history DTCs? | Go to DTC indicated as being either current or history. | Go to Step 3 | |||||||||
Test the following circuits of the TCM for an open or high resistance:
Refer to Section 12 Wiring Diagrams for references. Did you find and correct the condition? | Go to Step 7 | Go to Step 4 | |||||||||
4 | Test the CAN serial data low circuit and the CAN serial data high circuit between the engine control module (ECM) and TCM for the following conditions:
Refer to Wiring Systems for assistance. Did you find and correct the condition? | Go to Step 7 | Go to Step 5 | ||||||||
5 | Inspect for poor connections at the harness connector of the ECM. Refer to Wiring Systems. Did you find and correct the condition? | Go to Step 7 | Go to Step 6 | ||||||||
6 | Replace the TCM. Refer to Transmission Control Module Replacement. Did you complete the replacement? | Go to Step 7 | -- | ||||||||
Perform the following operations for confirm the repair:
Does the DTC reset? | Go to Step 2 | System OK | |||||||||
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | |||||||||||
