For 1990-2009 cars

### Circuit Description

Important: Do not perform this check if no driveability complaint exists.

The Diagnostic System Check-Engine Controls is an organized approach to identifying a problem created by an electronic engine control system malfunction. The Diagnostic System Check-Engine Controls is the starting point for any driveability complaint diagnosis. This directs the service technician to the next logical step in order to diagnose the complaint. Understanding the table and using it correctly will reduce diagnostic time, and will prevent the replacement of good parts.

### Test Description

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

1. In order to correctly diagnosis any driveability malfunctions, the scan tool must be able to power-up.

2. The diagnostic tables in this portion of the service manual are designed for use with a properly functioning scan tool. Serial data communication must be corrected before beginning any other diagnostic procedures. Class 2 serial data will not transmit if the system voltage is less than 9.0 volts or more than 16.0 volts.

3. By storing the Freeze Frame and Failure Records data on the scan tool, an electronic copy of the data is created when the malfunction occurred. This information is stored on the scan tool and can be referred to later. Type C DTCs do not store Freeze Frame data. If this option is not available, manually record the information for later reference.

4. If multiple DTCs are stored, diagnose in the following order:

1. | System voltage DTCs

2. | PCM Error DTCs

3. | Component level DTCs, or DTCs that indicate a malfunctioning part

4. | System level DTCs, or DTCs that indicate a system malfunction.

5. After the engine is at normal operating temperature, comparison of actual control system data with the typical values is a quick way to determine if any parameter is not within limits. Keep in mind that a base engine problem such as advanced cam timing may substantially alter sensor values.

   Inspect the following sensors for proper operation:

• | The engine coolant temperature (ECT) sensor -- Look for an initial coolant temperature reading that is close to ambient, then observe the rise in temperature to the normal operating temperature while the engine is warming up.

• | The throttle position (TP) sensor -- Look for proper sweep from 0 percent to 100 percent.

• | The manifold absolute pressure (MAP) sensor -- Look for quick changes during changes in various engine loads.

• | The oxygen sensor (O2S 1) --Look for proper rich/lean and lean/rich sweeps in operation.

• | The idle air control (IAC) valve --Look for proper idle control and proper transition while operating the high load components such as the air-conditioning (A/C) control.

• | Inspecting the sensors for proper operation during warm-up can be a crucial step in correctly diagnosing any driveability concern. Careful observation of these sensors during engine warm-up may reveal a slow responding sensor or a sensor that malfunctions only within a small portion of its range.

• | Review any published service bulletins that relate to the exhibited symptoms or to components operation.

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

• | Do NOT perform this test if no driveability condition exists.

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

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

• | Do NOT clear the DTCs unless the diagnostic instructs you to do so.

• | If there is a condition with the starter system, refer to Diagnostic System Check - Engine Electrical in Engine Electrical.

• | Ensure the battery is fully charged and the cables are clean and tight.

• | Ensure the PCM grounds are clean, tight, and in the proper location.

1. Connect a scan tool to the data link connector (DLC).
2. Turn ON the ignition, with the engine OFF.

Does the scan tool power-up?

Go to Step 2

Go to Scan Tool Does Not Power Up

2 | Does the scan tool display PCM data? | Go to Step 3 | Go to Scan Tool Does Not Communicate with Class 2 Device
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 | Use the scan tool in order to check the following modules for DTCs:

1. PCM
2. BCM

Does the scan tool display any PCM DTCs?

Go to Step 5

Go to Step 7

5 | Record the Freeze Frame and Failure Records information with the scan tool. Did you complete the action? | Go to Step 6 | --
6 | Were any of the PCM DTCs P0601, P0602, or P1621? | Go to DTC P0601, P0602, P0603, P0604, P0605, P0606, P0607, P1600, P1621, P1627, P1680, P1681, P1683, or P2610 | Go to Diagnostic Trouble Code (DTC) List
7 | Were any BCM DTCs set? | Go to Diagnostic Trouble Code (DTC) List | Go to Step 8
8 | Is the customer's concern with the Inspection/Maintenance (I/M) testing? | Go to Inspection/Maintenance (I/M) System Check | Go to Step 9
9 |

1. Allow the running engine to reach operating temperature.
2. Compare the scan tool data with the typical values shown in the Scan Tool Data list.

Are the display values normal or within typical ranges?

Go to Step 10

Go to Diagnostic Trouble Code (DTC) List

10 | If the customer's concern is a symptom, refer to the following tables:

• | Hard Start in Engine Controls

• | Surges/Chuggles in Engine Controls

• | Lack of Power, Sluggishness, or Sponginess in Engine Controls

• | Detonation/Spark Knock in Engine Controls

• | Hesitation, Sag, Stumble in Engine Controls

• | Cuts Out, Misses in Engine Controls

• | Poor Fuel Economy in Engine Controls

• | Rough, Unstable, or Incorrect Idle and Stalling in Engine Controls

• | Dieseling, Run-On in Engine Controls

• | Backfire in Engine Controls

• | Malfunction Indicator Lamp (MIL) Inoperative in Engine Controls

• | Malfunction Indicator Lamp (MIL) Always On in Engine Controls

Did you complete the action?

System OK

Go to Intermittent Conditions