For 1990-2009 cars
Engine Controls Components
Cell 21: MIL and DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The data link connector (DLC) provides communication with the powertrain control module (PCM). The DLC is located under the instrument panel. The DLC links a scan tool to the PCM serial data stream. The list below describes common uses of the scan tool.

• | Identifying saved 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. The scan tool must use the correct power feed.

Correctly select the model year, the carline, and the VIN code on the scan tool. If the scan tool operates incorrectly, test the scan tool on another vehicle in order to ensure that the scan tool is causing the malfunction.

Inspect in detail any circuitry that is suspected of causing an intermittent malfunction for the following conditions:

• | Backed out terminals.

• | Incorrect mating of terminals.

• | Broken electrical connector locks.

• | Incorrectly formed terminals or damaged terminals.

• | Faulty terminal-to-wire connections.

• | Physical damage to the wiring harness.

• | A broken conductor inside the wire insulation.

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

### Test Description

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

1. The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the applicable freeze frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.

2. This step checks if the scan tool will turn ON.

3. This step checks if the scan tool can establish communication on the PCM serial data line.

   This step checks for B+ at the DLC.

4. This step checks for B+ at the DLC.

5. This step checks the ground circuits at the DLC.

6. This step checks for a fault in the serial data circuit or for a faulty scan tool.

7. The PCM supplies a low current voltage on the serial data circuit. The normal circuit low current will NOT illuminate a test lamp. If the circuit is shorted to battery positive voltage, the higher current will illuminate the test lamp.

8. The scan tool may be damaged by high current flow on the serial data circuit at DLC terminal 7. Check the scan tool for correct operation on a known good vehicle that uses terminal 7 of the DLC for serial data communication.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install a scan tool.
2. Turn ON the ignition, leaving the engine OFF.

Does the scan tool turn ON?

--

Go to Step 3

Go to Step 5

3 | Attempt to establish communication with the powertrain control module (PCM). Does the scan tool display any PCM data? | -- | System OK | Go to Step 4
4 |

1. Check that all of the following scan tool selections are correct:

• | The model year

• | The carline or the truckline

• | The engine option (VIN)

2. Correct any error in selections.

Does the scan tool display the engine data?

--

System OK

Go to Step 9

5 |

1. Turn ON the ignition, leaving the engine OFF.
2. Measure the voltage from terminal 16 of the DLC to ground with a DMM.

Is the voltage near the specified value?

B+

Go to Step 6

Go to Step 8

6 | Probe the DLC terminals 4 and 5 with a test lamp connected to B+. Did the test lamp illuminate for both circuits? | -- | Go to Step 14 | Go to Step 7
7 | Repair the open in the DLC ground circuits. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 2 | --
8 | Repair the open or the short in the battery positive voltage circuit to the DLC. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 2 | --
9 | Measure the voltage from terminal 7 of the DLC to ground with a DMM. Is the voltage that was measured equal to or more than the specified value? | 11 volts | Go to Step 10 | Go to Step 12
10 | Connect a test lamp between the DLC connector terminal 7 and a ground. Does the test lamp illuminate? | -- | Go to Step 11 | Go to Step 14
11 | Repair the short to battery positive voltage in the serial data circuit. Scan tool damage may have occurred. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 3 | --
12 | Repair the open or the short to ground in the serial data circuit between the PCM and the DLC. Refer to Wiring Repairs in Wiring Systems. Was a repair necessary? | -- | Go to Step 3 | Go to Step 13
13 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 3 | --
14 |

1. Check the electrical connections of the DLC connector and of the scan tool for any of the following:

• | Bent or damaged electrical terminals

• | Loose or pushed back electrical terminals

• | Correct mating of the connectors

2. Repair as necessary.

Was a repair necessary?

--

Go to Step 2

Go to Step 15

15 |

1. The scan tool is faulty. Refer to the scan tool manual for repair information.
2. Repair or replace the scan tool.

Is the action complete?

--

Go to Step 2

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