Circuit Description
The engine control module (ECM) sends engine coolant temperature data to the transmission control module (TCM) through a communication network called the GM Local Area Network (GMLAN). Two circuits are used to communicate GMLAN data between the ECM/TCM and other modules. The TCM uses this engine coolant temperature data to initiate warm-up shift patterns and to establish default transmission fluid temperature (TFT) values.
A fault in the GMLAN will not cause DTC P0115 to set by itself. If a GMLAN fault occurs, other DTCs will set before DTC P0115.
When the TCM receives invalid engine coolant temperature data from the ECM, then DTC P0115 will be set, which is a type 'C' DTC.
Conditions for Running the DTC
| • | Ignition voltage is between 8-18 volts. |
| • | Engine speed is between 450 and 6,800 RPM. |
| • | Engine run time is greater than 5 seconds. |
| • | No other GMLAN errors are present. |
Conditions for Setting the DTC
The ECM GMLAN message received by the TCM does not contain a valid engine coolant temperature value for 2 seconds.
Action Taken When the DTC Sets
| • | The TCM does not request the powertrain interface module (PIM) to activate the check powertrain malfunction indicator lamp (MIL). |
| • | The TCM uses 25°C as a default engine coolant temperature value. |
| • | The TCM records the operating conditions when the 'Conditions for Setting the DTC' are met. The TCM stores this information as a Failure Record. |
| • | The TCM stores DTC P0115 in TCM history. |
Conditions for Clearing the DTC
| • | Tech 2 can clear the DTC. |
| • | The TCM clears the DTC from its memory (history DTC) if the vehicle completes 40 warm-up cycles without a non-emission related DTC occurring. |
| • | The TCM cancels the DTC default actions when the fault no longer exists and the DTC passes. |
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 | |||||||
2 |
Did you record any ECM DTCs? | Go to Step 3 | |||||||
3 |
Did DTC P0115 reset? | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections | ||||||
4 | Did other DTCs set? | Go to Step 5 | |||||||
5 | Replace the TCM. Refer to Transmission Control Module Replacement. Is the replacement complete? | Go to Step 6 | -- | ||||||
6 | Perform the following operation to verify the repair:
Does the DTC reset? | Go to Step 7 | Go to Step 2 | ||||||
7 | Use Tech 2 to read DTC information. Does Tech 2 display any DTCs that have not been diagnosed and rectified? | System OK | |||||||
When all diagnosis and repairs are completed, clear all DTCs and verify correct operation. | |||||||||
