A-2 ~ Data Link Connector (DLC) Diagnosis and MIL "ON"

Data Link Connector (DLC) Circuit:

Circuit Description
The provision for communicating with the Powertrain Control Module (PCM) is the Data Link Connector (DLC). The DLC is located under the instrument panel. The DLC is used to connect to a scan tool. Some common uses of the scan tool are listed below:
- Identifying stored DTCs.
- Clearing DTCs.
- Performing output control tests.
- Reading serial data.

Battery power and ground are supplied to the scan tool from the DLC. The Class 2 serial data circuit to the DLC allows the PCM to communicate with the scan tool. A UART serial data line is used to communicate with other modules such as the Electronic Brake Control Module (EBCM), and the Supplemental Inflatable Restraint (SRS) system.

Diagnostic Aids
Some scan tools may require an external power supply. Make sure your scan tool is using the correct power feed.
Ensure that the correct application (model year, engine, VIN code) has been selected on the scan tool. If communication still cannot be established, try the scan tool on another vehicle to ensure that the scan tool, Vehicle Interface Module (VIM), or cables are not the cause of the condition.
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.
Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for the following:
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Physical damage to the wiring harness
- Corrosion

Table A-2 - Data Link Connector (DLC) Diagnosis and MIL "ON" Steady (1 Of 2):

Table A-2 - Data Link Connector (DLC) Diagnosis and MIL "ON" Steady (2 Of 2):

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. The On Board Diagnostics (OBD) System Check prompts the Technician to complete some basic checks and store the Freeze Frame Data and the Failure records on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. This information on the scan tool can be referred to later.
2. When the Ignition is turned "ON, the Malfunction Indicator Lamp (MIL) should momentarily flash "ON" then "OFF" then The MIL should turn "OFF" when the vehicle is running if no emission related DTCs are set.
3. If the scan tool requires an external power supply, check the external supply for proper voltage and ground as well as the voltage and ground supplies in the DLC.
6. Unlike the UART serial data circuit, the only time any the Class 2 serial data circuit has any voltage on it is when a scan tool asks the PCM for information and the PCM sends the information out.
11. If the no voltage condition was due to a blown fuse, locate and repair any shorts that may have caused the fuse to blow before replacement.
12. Refer to Diagnostic Aids if the scan tool will not display scan data. If you were sent here from the OBD System Check table, return to that table and complete the diagnostics there.
14. Replacement PCM must be reprogrammed. Refer to the latest Techline information for programming procedures.
18. The scan tool, VIM or associated cables could be faulty. Refer to the scan tools manual for repair information.