Diagnostic System Check

Description

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

Do not perform this check if no driveability concern exists. A driveability condition includes all PCM controlled systems and components.

The DTCs associated with the automatic transmission are:

^ DTCs P0502 and P0503.
^ Any 700 (except DTC P0704) and 1800 series DTCs (i.e. DTC P07XX and P18XX).

This vehicle is equipped with a Powertrain Control Module (PCM) utilizing an Electrically Erasable Programmable Read Only Memory (EEPROM). Program the new PCM when diagnostics call for replacement of the PCM. When the PCM is replaced, the following must be performed.

^ The PCM must be programmed.
^ The CKP System Variation Learn Procedure.
^ The Idle Learn Procedure.
^ The Engine Oil Life Monitor reset procedure.

When the PCM power is interrupted or the PCM is reprogrammed, the PCM Idle Learn Procedure must be performed.

Diagnostic Aids

^ If an intermittent condition exists, inspect the PCM wiring harnesses for improper installation of electrical components. Inspect for aftermarket theft deterrent devices, lights, and cellular phones. Ensure that no aftermarket equipment is connected to the Class 2 circuit. A cellular phone signal communication may cause an intermittent condition.
^ The following may cause an intermittent:
- Poor connections; Refer to Intermittents and Poor Connections Diagnosis. Testing and Inspection
- Corrosion
- Mis-routed harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation.
^ If multiple DTCs are set, inspect the IGN relay for proper operation. The following components are powered by the IGN relay:
- Injectors/Ignition coils
- A/C system
- Transmission
- [1][2]EVAP solenoid and EVAP Vent Valve
- MAF sensor
- Heated Oxygen Sensors For an intermittent, refer to Symptoms. Testing and Inspection

Test Description

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

1. Use a properly functioning scan tool with the diagnostic tables. DO NOT use the Clear Info function unless instructed by a diagnostic procedure.
3. An Ignition 1 voltage that is too low may cause the following conditions:
^ A no start
^ Stalling
^ High idle
^ An inoperative scan tool
5. This step determines if a DTC is set for the Vehicle Theft Deterrent (VTD) system. A VTD DTC set causes the engine from starting.
6. If multiple DTCs are stored, diagnose in the following order of priority:
1. PCM failure DTCs (P0601, P0602, P0604)
2. System Voltage DTCs
3. Component level DTCs (Sensors, Solenoids, Relays etc.). Multiple DTCs within this category should be diagnosed in numerical order starting with the lowest numbered DTC.
4. System level DTCs (Misfire, Fuel Trim, etc.)

For Automatic Transmission DTCs, refer to Diagnostic Trouble Code Identification.

It is beneficial to review the Freeze Frame Data and/or Fail Records. Use the odometer information and the fail counter in order to determine how frequently and how recently the DTC set. This information and the other operating conditions when the DTC set may help diagnose an intermittent condition. Capturing the stored info preserves data that the PCM will lose when instructed to Clear Info at the end of a diagnostic table, or if you disconnect the PCM or replace the PCM during a diagnostic procedure. The scan tool stores the data in the scan tool's memory. Review the captured info at the end of the diagnostic procedure in order to catch the next DTC in the event there are multiple DTCs stored. Follow the order of priority as listed above.

7. Compare actual control system data with the values in the Engine Scan Tool Data List to determine if any parameter is not within limits. Keep in mind that a base engine condition (i.e. advanced cam timing) may substantially alter sensor values. If the actual data does not correspond with the values in the Engine Scan Tool Data List, refer to the appropriate system/component diagnostic aids or test descriptions.