Engine Control Module: Description and Operation

PURPOSE
The Digifant control module determines the injector opening time based on inputs it receives from the following components:

^ The Manifold Absolute Pressure (MAP) sensor (G71)
^ The Intake Air Temperature (IAT) sensor (G42) and CO potentiometer (G74)
^ The Heated Oxygen Sensor (HO2S) (G39)
^ And the Engine Coolant Temperature (ECT) sensor (G62)

OPERATION
- The (J169) Engine Control Module (ECM) is equipped with a Diagnostic Trouble Code (DTC) Memory.

- If malfunctions occur in the sensors and/or components that are monitored, these are stored in the DTC Memory with data on the type of malfunction.

- DTC display occurs after activation of the Scan Tool (ST).

- DTC Memory must be erased after the malfunctions have been corrected or repaired.

- Malfunctions that affect Oxygen sensor control can only be read accurately after a test drive of at least 5 minutes.

Malfunctions such as intermittent open circuits or loose terminals are stored and displayed as follows:

- If malfunctions occur for a maximum of 5 seconds, they are stored and considered to be "sporadic' and when displayed, they will have the letter-code "SP".

- If malfunctions are present for more than 5 seconds, they are stored as DTC's and will be displayed like a permanent malfunction even though the malfunction is not occurring at the time of the reading.

- California vehicles are equipped with a malfunction indicator (MIL) lamp.

- The MIL lamp in the instrument panel must light up when the ignition is turned ON and go out after the engine starts. As long as malfunctions occur in monitored sensors or components and the required DTC conditions are fulfilled, the MIL lamp will remain lit, even with the engine running.

STANDARD FEATURES
- Diagnostic Trouble Code Memory (formerly Fault Memory).
- Rapid data transfer.
- Output Diagnostic Test Mode (DTM), (vehicles after 6/91, formerly Output Check Diagnosis).
- Engine Basic Setting, (vehicles after 10/91).
- Read measurement block (Function 08).
- Read individual measurements, (vehicles after 10/91).
- Malfunction Indicator Lamp in instrument panel (California ONLY).