Description of On-Board Diagnostics

Diagnostic Trouble Code Chart - Part 1:

Diagnostic Trouble Code Chart - Part 2:

DIAGNOSTIC SYSTEM DESCRIPTION

The Engine Control Module (ECM) contains a built-in self-diagnosis system which detects troubles within the engine signal network and a Malfunction Indicator Lamp (MIL) or "CHECK" on the instrument panel which is used to indicate the stored code.

By analyzing various signals ECM detects system malfunctions which are related to the various operating parameter sensors or actuators. The ECM stores the diagnostic code associated with the detected failure until the diagnosis system is cleared by removing the 15 Amp EFI fuse with the ignition switch OFF.





The "CHECK" light (MIL) on the instrument panel informs the driver that a malfunction has been detected.

The light goes off automatically when the diagnostic codes have been cleared.

MALFUNCTION INDICATOR LAMP (MIL) - CHECK ENGINE LIGHT

1. The Malfunction Indicator Lamp will come ON when the Ignition Switch is placed at ON and the engine is NOT RUNNING.

2. When the engine is started, the MIL should go OFF.

If the light remains ON, the diagnosis system has detected a malfunction or abnormality in the system.

2 TRIP DETECTION LOGIC:

Two Trip Detection Logic - Driving Pattern:

Certain Diagnostic Trouble Codes (DTC) (21, 25, 26 and 71), can be triggered by driving conditions without a malfunction present. To improve self diagnostic reliability, "2nd trip" detect logic is used.

When an a fault related to any of the above DTC's is detected, the ECM retains a temporary record of the fault in memory. An actual code is set only if the same fault is recorded during the next ignition/driving cycle.

The MIL is only illuminated after the "2nd trip."

Because the ECM must see the fault for 2 consecutive trips, the chances of a false code are greatly reduced.

DIAGNOSIS

A specific driving pattern must be followed to recreate a fault code.

^ Drive the vehicle in the same manner the customer has indicated caused the fault.
^ Stop vehicle and turn ignition OFF.
^ Restart vehicle and repeat test-drive.


VERIFICATION OF REPAIR

After repairs, clear ECM memory and follow the same driving pattern used for code detection.