For 1990-2009 cars

### Circuit Description

The provisions for communicating with the engine control module (ECM), electronic brake control module (EBCM), SIR module, immobilizer module, and the theft deterrent module are located in the data link connector (DLC). The DLC is located under the instrument panel (I/P). The 16 pin DLC provides the serial data signals at terminals 7 (ECM, TCM, immobilizer serial data), 8 (theft deterrent serial data), 12 (ABS serial data), and 13 (SIR serial data). The DLC is used to link a scan tool to the ECM, EBCM, SIR, immobilizer, and theft control modules serial data stream. Some common uses of the scan tool are listed below:

• | Identifying the stored diagnostic trouble codes (DTCs)

• | Reading the serial data stream

• | Clearing the DTCs

• | Storing the Freeze Frame data

### Diagnostic Aids

Some scan tools may require an external power supply. Ensure the scan tool is correctly connected to the power feed.

Ensure that the correct application (model year, carline, VIN code) has been selected on the scan tool. If communications are still not established, try the scan tool on another vehicle in order to ensure that the scan tool or the connecting cables are not the cause of the malfunction. Always try the scan tool on a vehicle that uses the same DLC terminal for serial data communication.

Any circuitry that is suspect to an intermittent complaint should be thoroughly inspected for the following:

• | Backed-out terminals

• | Improper mating of terminals

• | Broken electrical connector locks

• | Improperly formed or damaged terminals

• | Faulty terminal-to-wiring connections

• | Physical damage to the wiring harness

• | A broken conductor inside the wire insulation

• | Corrosion of the electrical connections, the splices, or the terminals

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step checks whether the scan tool can communicate with other control modules on the vehicle. If the scan tool can communicate with one of the other modules then the DLC connector, the shared circuits, and the scan tool are OK.

2. This step checks whether the ECM is receiving ignition positive voltage from the fuse F16 when the ignition is ON. The ECM cannot provide serial data without ignition positive voltage.

3. This step checks for a high resistance or an open/short in the ECM serial data circuit.

4. This step checks the ECM DLC Diagnostic circuit high resistance or open/short. This could cause the ECM not to communicate.

5. This step checks to see if the EBCM is not communicating with the scan tool.

6. This step checks to see if the SIR system is not communicating with the scan tool.

7. This step checks to see if the theft deterrent-immobilizer system is not communicating with the scan tool.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Data Link Connector Schematics
1 | Have you performed the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Does the scan tool power up? | Go to Step 3 | Go to Scan Tool Does Not Power Up
3 | Does the scan tool communicate with the engine control module (ECM)? | Go to Step 9 | Go to Step 4
4 | With the ignition OFF:

1. Disconnect the ECM connector.
2. Turn ON the ignition.
3. Test the ECM battery positive (B+) and/or ignition voltage circuits with a test lamp connected to ground.

Does the test lamp illuminate for all circuits?

Go to Step 5

Go to Step 24

5 | With the ECM still disconnected, test the ECM ground circuits with a test lamp connected to B+. Does the test lamp illuminate for all ground circuits? | Go to Step 6 | Go to Step 24
6 |

1. Reconnect the ECM connector.
2. Connect the scan tool.
3. Turn ON the ignition, with the engine OFF.

Does the scan tool display serial data?

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 7

7 | Test the serial data circuit for an open, high resistance, or a short circuit. Refer to Circuit Testing . Did you find and correct the condition? | Go to Step 29 | Go to Step 8
8 | Test the data link connector (DLC) diagnostic circuit for an open, high resistance or a short circuit. Refer to Circuit Testing . Did you find and correct the condition? | Go to Step 29 | Go to Step 25
9 | Does the scan tool communicate with the electronic brake control module (EBCM)? | Go to Step 14 | Go to Step 10
10 | Test the EBCM battery positive (B+) and/or ignition voltage circuits with a test lamp to ground. Does the test lamp illuminate for all circuits? | Go to Step 11 | Go to Step 24
11 | Test the EBCM ground circuits with a test lamp connected to B+. Does the test lamp illuminate for all circuits? | Go to Step 12 | Go to Step 24
12 | Test the EBCM serial data circuit for an open, high resistance, or short circuit. Refer to Circuit Testing . Did you find and correct the condition? | Go to Step 29 | Go to Step 13
13 | Inspect the EBCM connectors. Refer to Wiring Repairs or Connector Repairs . Did you find and correct the condition? | Go to Step 29 | Go to Step 26
14 | Does the scan tool communicate with the SIR module? | Go to Step 19 | Go to Step 15
15 | Test the SIR module battery positive (B+) and/or ignition voltage circuits with a test lamp to ground. Does the test lamp illuminate for all circuits? | Go to Step 19 | Go to Step 24
16 | Test the SIR module ground circuits with a test lamp connected to B+. Does the test lamp illuminate for all circuits? | Go to Step 17 | Go to Step 24
17 | Test the SIR serial data circuit for an open, high resistance, or short circuit. Refer to Circuit Testing . Did you find and correct the condition? | Go to Step 29 | Go to Step 18
18 | Inspect the SIR module connectors. Refer to Wiring Repairs or Connector Repairs . Did you find and correct the condition? | Go to Step 29 | Go to Step 27
19 | Does the scan tool communicate with the theft deterrent module? | Go to Step 29 | Go to Step 20
20 | Test the theft deterrent module battery positive voltage B+ and/or ignition voltage circuits with a test lamp to ground. Does the test lamp illuminate for all circuits? | Go to Step 21 | Go to Step 24
21 | Test the theft deterrent module ground circuits with a test lamp connected to B+. Does the test lamp illuminate for all circuits? | Go to Step 22 | Go to Step 24
22 | Test the theft deterrent serial data circuit for an open, high resistance, or short circuit. Refer to Circuit Testing . Did you find and correct the condition? | Go to Step 29 | Go to Step 23
23 | Inspect the theft deterrent module connectors. Refer to Wiring Repairs or Connector Repairs . Did you find and correct the condition? | Go to Step 29 | Go to Step 28
24 | Repair the circuit as necessary. Refer to Wiring Repairs or Connector Repairs . Is the action complete? | Go to Step 29 | --
25 | Replace the ECM. Is the action complete? | Go to Step 29 | --
26 | Replace the EBCM. Refer to Brake Pressure Modulator Valve Assembly Replacement . Is the action complete? | Go to Step 29 | --
27 | Replace the SIR module. Refer to Inflatable Restraint Sensing and Diagnostic Module Replacement . Is the action complete? | Go to Step 29 | --
28 | Replace the theft deterrent module. Refer to Theft Deterrent Module Replacement . Is the action complete? | Go to Step 29 | --
29 | Operate the system in order to verify the repair. Is the action complete? | System OK | Go to Step 3