For 1990-2009 cars

### Circuit Description

The Class II serial data circuit to the DLC allows bi-directional communication between the PCM and the scan tool. If communication between the scan tool and the PCM cannot be established, the procedure in the DLC Diagnosis table should be used to diagnose the condition.

### Diagnostic Aids

Check the following items:

• | For the PCM to establish communication with the scan tool, system voltage must be between 9.0 and 16.0 volts. If system voltage is not within this range, refer to Charging System Check for diagnosis.

• | Ensure that the correct application (model year, carline, 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, 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. Check for poor connections or a damaged harness. Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs .

### Test Description

The number below refers to the step number on the Diagnostic Table.

1. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming in Powertrain Control Module (PCM) and Sensors.

#### DLC Diagnosis

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

1. Turn the ignition ON, engine OFF.
2. Connect a test light between the DLC battery feed and ground circuits. (Terminals 4 and 5)

Is the test light ON?

--

Go to Step 4

Go to Step 3

3 | Probe the DLC battery feed circuit with a test light to chassis ground. Is the test light ON? | -- | Go to Step 9 | Go to Step 10
4 |

1. Turn the ignition ON, engine OFF.
2. Probe the Class 2 serial data circuit at the DLC with a DMM to ground.

Does the voltage measure the specified value?

0.0V

Go to Step 5

Go to Step 7

5 |

1. Turn the ignition OFF , disconnect the PCM.
2. Turn the ignition ON , engine OFF.
3. Probe the Class 2 serial data circuit at the DLC with a DMM connected to battery positive voltage.

Does the voltage measure the specified value?

0.0V

Go to Step 6

Go to Step 8

6 |

1. Check the Class II serial data circuit for an open between the DLC and the PCM
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 11

7 |

1. Check the Class II serial data circuit for a short to voltage.
2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 11

8 | Locate and repair short to ground in the Class II serial data circuit. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
9 | Locate and repair open in the DLC ground circuit(s). (Terminal 4 or 5) Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
10 | Locate and repair open or short to ground in the DLC battery feed circuit. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
11 | Important: : Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --