For 1990-2009 cars

Refer to Engine Control Schematic

#### Power, Ground, MIL, and DLC

Engine Controls Components
Powertrain Control Module Description
Fuel System
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Power Distribution Schematics
Power Distribution Schematics
Power Distribution Schematics
Power Distribution Schematics
Instrument Cluster: Analog Schematics
Ground Distribution Schematics
Power Distribution Schematics
Instrument Cluster: Analog Schematics
Data Link Connector Schematics
Ground Distribution Schematics
Ground Distribution Schematics
.

### Circuit Description

The Powertrain On Board Diagnostic System Check must be the starting point for any driveability complaint diagnosis. Before using this procedure, you should perform a careful visual/physical check of the powertrain control module (PCM) and engine grounds for being clean and tight. The Powertrain On-Board Diagnostic System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction.

### MIL Operation

The Malfunction Indicator Lamp (MIL) is located on the instrument panel and is displayed as CHECK ENGINE lamp.

#### MIL Function

• | The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible

• | The MIL illuminates during a bulb test and a system test

• | A DTC will be stored if a MIL is requested by the diagnostic

#### MIL Illumination

• | The MIL will illuminate with ignition switch ON and the engine not running

• | The MIL will turn OFF when the engine is started

• | The MIL will remain ON if the self-diagnostic system has detected a malfunction

• | The MIL may turn OFF if the malfunction is not present

• | If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON.

• | If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

#### Powertrain On Board Diagnostic (OBD) System Check

Perform the Powertrain On Board Diagnostic (OBD) System Check, when the following conditions are present:

• | The MIL does not turn ON when the ignition switch is turned to the RUN position. See above for MIL Operation

• | The MIL remains ON while the engine is running

• | The MIL is flashing while the engine is running

• | A driveability symptom is determined

### Diagnostic Aids

An intermittent may be caused by a faulty connection, rubbed-through wire insulation or a wire broken inside the insulation. Check for faulty connections or a damaged harness. Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, faulty terminal-to-wire connection, and a damaged harness.

### Test Description

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

1. The MIL should be ON steady with the key ON, engine OFF. If not, the No Malfunction Indicator Lamp table should be used to isolate the malfunction.

2. This test ensures that the PCM is capable of transmitting Class 2 serial data to the DLC and that the Class 2 Data circuit is not open or shorted. If you find a problem and a malfunctioning scan tool is suspected, try the scan tool on another vehicle in order to verify operation. If a DLC problem exists, the DLC Diagnosis table should be used to diagnose the condition.

3. If the engine will not start, the Engine Cranks But Will Not Run table should be used to diagnose the condition.

4. The scan tool may display DTCs which are diagnosed in Automatic Transmission/Transaxle Diagnosis. If multiple DTCs are stored, diagnose each DTC according to the following priority:

• | PCM Error DTCs

• | System Voltage DTCs

• | Component Level DTCs such as switches, sensor range/performance, sensor high voltage, sensor low voltage, and ODMs

• | System level DTCs such as Fuel Trim, Misfire, EGR Flow, TWC System, Idle Control System, HO2S Response, or HO2S Transition Time Ratio

5. A scan tool parameter which is not within the typical range may help to isolate the area which is causing the problem.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Important::

• | Search for applicable service bulletins before proceeding with the diagnosis.

• | Do not turn OFF the ignition when performing this diagnostic table.

• | Do not perform this test if no drivability condition exists.

• | Unless instructed, do not clear any DTCs.

1. Turn ON the ignition, with the engine OFF.
2. Observe the MIL.

Is the MIL illuminated?

--

Go to Step 2

Go to Malfunction Indicator Lamp (MIL) Inoperative

2 |

1. Turn OFF the ignition.
2. Install a scan tool.
3. Turn ON the ignition, with the engine OFF.
4. With a scan tool, attempt to display PCM data.

Does the scan tool display PCM data?

--

Go to Step 3

Go to Data Link Connector Diagnosis

3 | Attempt to start the engine. Does the engine start and continue to run? | -- | Go to Step 4 | Go to Engine Cranks but Does Not Run
4 | Important: If the scan tool indicates any DTCs set, record Freeze Frame/Failure Records. Use the scan tool in order to display DTCs. Does the scan tool indicate that any DTCs set? | -- | Go to applicable DTC table | Go to Step 5
5 | With a scan tool, compare the PCM data to the Scan Tool Data List . Does the scan tool indicate PCM values equal or within the typical values? | -- | System OK | Go to Component System Checks