Data Link Communications System

CIRCUIT DESCRIPTION
The controller area network (CAN) is a high speed system for sharing data. The circuit consists of a two wire twisted pair connecting the ECM to the TCM and a second twisted pair connecting the ECM to the EBCM.

CONDITIONS FOR RUNNING THE DTC
The CAN circuits are monitored continuously by the modules on the circuit. The only requirement is that the modules are in a ON power mode.

CONDITIONS FOR SETTING THE DTC
The module setting the DTC has attempted to establish communications on the CAN circuits more than 7 times. After the seventh attempt, the module sets this DTC.

ACTION TAKEN WHEN THE DTC SETS
Besides storing the DTC as both current and history, the modules on the CAN network each take separate actions as listed:
^ Engine Control Module (ECM):
- Turn ON the MIL during the second consecutive drive cycle with the error detected.
- Record the operating conditions at the time of turning on the MIL and store the data as freeze frame information.
^ Transmission Control Module (TCM):
- Turn ON the Service Transmission Lamp (STL) when the first error is detected.
- Send a request to the ECM to turn ON the MIL during the second consecutive drive cycle with the error detected.
- Operate in the Default Mode. Refer to Electronic Component Description in Automatic Transmission-4L30-E.
^ Electronic Brake Control Module (EBCM):
- Traction Control System (TCS) is disabled.
- Turn ON the TC indicator.

CONDITIONS FOR CLEARING THE MIL/DTC
The MIL, STL and TC indicators are cleared, turned OFF, and the DTC cleared by a different strategy for each module:
^ ECM:
- If the fault is not detected for three consecutive drive cycles the current DTC is cleared and the MIL is turned OFF.
- The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
- The history DTC is cleared if there is a KAM reset (battery disconnected).
^ TCM:
- If the fault is not detected for one drive cycle the current DTC is cleared and the STL is turned OFF.
- The history DTC is cleared if the malfunction does not reoccur for 40 consecutive drive cycles.
- The Default Mode transmission control is cancelled when the malfunction is not present and the ignition switch is OFF long enough for the TCM to power-down and reset.
^ EBCM:
- If the fault is not detected for one drive cycle the current DTC is cleared and the TC indicator is turned OFF.
- The history DTC is cleared if the malfunction does not reoccur for 100 consecutive drive cycles.

DIAGNOSTIC AIDS
Missing data from a module may assist in diagnosing this malfunction. Determine the module that is not communicating by observing the following:
^ ABS System (EBCM)
- Engine Speed (RPM) - This comes from the ECM.
- Delivered Engine Torque (%) - This comes from the TCM.
^ Transmission Data (TCM)
- Engine Speed (RPM) - This comes from the ECM.
- Vehicle Speed MPH) - This comes from the EBCM.
- MIL Request - This goes to the ECM.
^ Engine Data (ECM)
- Vehicle Speed MPH) - This comes from the EBCM.
- MIL Request - This comes from the TCM.

TEST DESCRIPTION

Steps 1-9:

The number(s) below refer to the step number(s) on the diagnostic table.
2. A communications failure to one or more modules of a data link circuit may cause the malfunction.
3. If a module is not transmitting the required data, the module receiving the data cannot detect the presence of the transmitting module
6. The TCM needs time to reset memory.