Initial Inspection

ON BOARD DIAGNOSTIC (OBD) SYSTEM CHECK
The On Board Diagnostic (OBD) System Check is an organized approach to identifying a problem caused by an electronic engine control system malfunction. It must be the starting point for any driveability complaint diagnosis because it directs the technician to the next logical step in diagnosing the complaint.
Use the "Typical Scan Tool Data Definitions" list for comparison after completing the OBD system check and finding the on board diagnostics functioning properly and no diagnostic trouble codes are displayed. The "Typical Scan Tool Definitions" are an average of display values recorded from normal operating vehicles. They are intended to represent what a normal functioning system should display.

NOTE: A scan tool that displays faulty data should not be used. The problem should be reported to the manufacturer. The use of a faulty scan tool can result in misdiagnosis and unnecessary parts replacement.
Only the parameters listed below are used for diagnosis. When a scan tool reads other parameters, the values are not recommended for use in diagnosis.
Whenever all the values are within the range illustrated, refer to Diagnosis by Symptom.

Symptom Related Diagnostic Procedures

Diagnostic Aids

NOTE: Do not clear Diagnostic Trouble Codes (DTCs) unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable freeze frame and failure records data.

On-Board Diagnostic (OBD) System Check Circuit Diagram:

- Inspect all related wiring and connections including the connections at the PCM. These may cause an intermittent malfunction.
- Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for the following:
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wiring connections
- Physical damage to the wiring harness
- Corrosion

Diagnostic Table:

Test Description
Numbers below refer to the step numbers on the Diagnostic Table.
1. When the ignition is turned "ON", the MIL will momentarily flash "ON" then "OFF" and remain "ON" until the engine is running if no DTCs are stored.
2. The diagnostic tables in this section are designed for use with a properly functioning scan tool. Serial data communications must be corrected before beginning any other diagnostic procedures. Class II Serial Data will not transmit if the system voltage is below 9.0 volts or above 16.0 volts.
4. Whenever multiple DTCs are stored, refer to the DTC Tables in the following order:
- PCM Error DTCs.
- System voltage DTCs.
- Component level DTCs (DTCs that indicate a faulty part).
- System level DTCs (DTCs that indicate a system fault).

5. By storing the Freeze Frame Data and the Failure records selection in the scan tool, an electronic copy of the freeze frame data and the failure records taken when the fault occurred is stored which can be referred to later.
7. Check the following sensors for proper operation:
- Engine Coolant Temperature (ECT) sensor for initial coolant temperature reading close to ambient, then observe the raise in temperature to operating temperature while the engine is warming up.
- Throttle Position (TP) sensor for proper sweep from 0% to 100%.
- Manifold Absolute Pressure (MAP) sensor for quick changes during changes in various engine loads.
- The Idle Air Control (IAC) valve for proper idle control and for proper transitions while operating high load components, such as A/C control.
- The Oxygen Sensor (O2S 1) for proper rich/lean and lean/rich sweep operation.

Scan Tool Data - Engine 1 Idle/Upper Radiator Hose Hot/Closed throttle/Park or Neutral/"Closed Loop"/ACC. "OFF"(1 Of 2):

Scan Tool Data - Engine 1 Idle/Upper Radiator Hose Hot/Closed throttle/Park or Neutral/"Closed Loop"/ACC. "OFF"(2 Of 2):

NOTE: Checking 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.
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 (i.e. advanced cam timing) may substantially alter sensor values.