Circuit Description
Important: Do not perform this check if no driveability complaint exists.
The Powertrain On-Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction. The Powertrain OBD system check 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.
Diagnostic Aids
Important: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records data.
| • | Review any published service bulletins that relate to the exhibited symptoms or the component operation. |
| • | Inspect all related wiring and connections at the Powertrain control module (PCM). Problems with wiring and connections may cause an intermittent malfunction. |
| • | Inspect any circuitry that is suspected of causing an intermittent complaint for the following conditions: |
| - | Backed-out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal-to-wire connections |
| - | Physical damage to the wiring harness |
| - | Corrosion |
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
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In order to correctly diagnosis any driveability malfunctions, the scan tool must be able to power-up.
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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.
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If multiple DTCs are stored, refer to the DTC Tables in the following order:
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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.
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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:
| 1. | PCM Error DTCs |
| 2. | System voltage DTCs |
| 3. | Component level DTCs, or DTCs that indicate a malfunctioning part |
| 4. | System level DTCs, or DTCs that indicate a system malfunction. |
| • | 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 | Value(s) | Yes | No | ||||||||||
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IMPORTANT:
Does the scan tool power-up? | -- | |||||||||||||
Does the scan tool display PCM data? | -- | |||||||||||||
Check for DTCs with the scan tool. Were any history or MIL request DTCs set? | -- | |||||||||||||
Record the Freeze Frame and Failure Records information with the scan tool. Is the action complete? | -- | -- | ||||||||||||
5 | Observe the malfunction indicator lamp (MIL). Is the MIL ON? | -- | ||||||||||||
6 | Command the MIL OFF with the scan tool. Does the MIL turn OFF? | -- | ||||||||||||
7 | Attempt to start the engine. Does the engine start and continue to run? | -- | ||||||||||||
Are the display values normal or within typical ranges? | -- | Go to Symptoms |
