For 1990-2009 cars
Engine Controls Components
Power, Ground, MIL, and DLC
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The provision for communicating with the control module is the data link connector (DLC). It is usually 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 diagnostic trouble codes (DTCs).

• | Clearing DTCs.

• | Performing output control tests.

• | Reading serial data.

Battery power and ground is supplied for the scan tool through 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), the supplemental inflatable restraint (SIR) system, and the instrument panel cluster (IPC).

### Diagnostic Aids

Ensure that the correct application--the model year, the car line, and the 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 or the cables are not the cause of the condition.

An intermittent may be caused by the following:

• | Poor connection

• | Rubbed-through wire insulation

• | Broken wire inside the insulation

Any circuitry that is suspected of causing an intermittent complaint should be thoroughly checked for the following conditions:

• | Backed-out terminals

• | Improper mating of terminals

• | Broken locks

• | Improperly formed or damaged terminals

• | Poor terminal-to-wiring connections

• | Physical damage to the wiring harness

• | Corrosion

### Test Description

Numbers below refer to the step numbers on the Diagnostic Table.

1. If the scan tool is using an external power supply, check the external supply for proper voltage and ground as well as the voltage and ground supplies in the DLC.

2. Unlike the UART serial data circuit, the only time the Class 2 serial data circuit has any voltage on it is when a scan tool ask the PCM for information and the PCM sends the information out.

3. Locate and repair any shorts that may have caused the fuse to open before replacement, if the no voltage condition was due to a open fuse.

4. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline information for PCM programming and Crankshaft Position System Variation Learn .

5. Refer to Diagnostic Aids if the scan tool will not display scan data. If the scan tool can communicate with the PCM and you were sent here from the Powertrain OBD System Check table, return to that table and complete the diagnostics there.

6. The scan tool or associated cables could be malfunctioning. Refer to the scan tools manual for repair information.

#### Data Link Connector (DLC) Diagnosis

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

1. Turn ON the ignition switch leaving the engine OFF.
2. Observer the Malfunction Indicator Lamp (MIL).

Is the MIL ON.

--

Go to Step 3

Go to Malfunction Indicator Lamp (MIL) Inoperative

3 | Install a scan tool. Does the scan tool power up? | -- | Go to Step 4 | Go to Step 5
4 |

1. Disconnect the scan tool.
2. Connect a DMM to ground.
3. Probe the Class 2 serial data terminal (cavity 2) at the DLC.

Does the DMM read the specified value?

0 V

Go to Step 6

Go to Step 7

5 |

1. Connect a DMM to ground.
2. Probe the DLC battery feed circuit terminal (cavity 16).

Does the DMM read the specified value?

B+

Go to Step 8

Go to Step 9

6 |

1. Connect a DMM to B+.
2. Probe the Class 2 serial data terminal (cavity 2) at the DLC.

Does the DMM read the specified value?

B+

Go to Step 10

Go to Step 11

7 |

1. Check the Class 2 serial data circuit for a short to voltage.
2. Repair the circuit as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 18

Go to Step 12

8 |

1. Connect a DMM to B+.
2. Probe the DLC ground circuit electrical terminals (cavities 4 and 5) .

Does the DMM read the specified value for both circuits?

B+

Go to Step 16

Go to Step 13

9 |

1. Check the DLC battery feed circuit for the following conditions:

• | Open circuit

• | Short to ground

2. Repair the circuit as necessary. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 18

--

10 |

1. Check the Class 2 serial data circuit for the following conditions:

• | Open circuit

• | Poor electrical connection

2. Repair the circuit as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 18

Go to Step 14

11 |

1. Check the Class 2 serial data circuit for a short to ground.
2. Repair the circuit as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 18

Go to Step 12

12 |

1. Turn OFF the ignition switch.
2. Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 18

--

13 |

1. Check the DLC ground circuits for the following conditions:

• | Open circuit

• | Poor electrical connections

2. Repair the circuit as necessary. Refer to Wiring Repairs .

Is the action complete?

--

Go to Step 18

--

14 | Reinstall the scan tool. Can the scan tool communicate with the PCM? | -- | Go to Step 18 | Go to Step 15
15 |

1. Install the scan tool on a another vehicle with Class 2 serial data.
2. Check the scan tool for proper operation.

Does the scan tool work properly on a different vehicle?

--

Go to Step 12

Go to Step 17

16 |

1. Check the DLC electrical terminals for the following conditions:

• | Proper wire tension

• | Excessive wiring resistance.

2. Repair the electrical terminals as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 18

Go to Step 17

17 |

1. Scan tool is malfunctioning.
2. Refer to the scan tools manual for repair information.

Is the action complete?

--

Go to Step 18

--

18 |

1. Using a scan tool, clear the DTCs.
2. Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 19

Go to Step 1

19 |

1. Allow engine to idle until normal operation temperature is reached.
2. Check if any DTCs are set.

Are any DTCs displayed that have not been diagnosed?

--

Go to Applicable DTC table

System OK