Diagnostic Test Mode Description

Memory Retention:

The Diagnostic Test Mode is divided into four specialized tests: Bulb Check, Diagnostic Test Mode, Heated Oxygen Sensor Monitor Test and Switch Monitor Test.

The Diagnostic Test Mode is not a conclusive test by itself, but is used as a part of the functional Quick Test diagnostic procedure. The processor (PCM) stores the Diagnostic Test Mode program in its permanent memory. When the Diagnostic Test Mode is activated, it checks the PCM by testing its memory integrity and processing capability, and verifying that various sensors and actuators are connected properly.

Unlike EEC-IV, no sensors or switches are exercised during a Diagnostic Test Mode. Also, any intermittent code will be stored in permanent memory until the starter is operated 50 times or until erased.



Bulb Check
With the ignition switch in the ON position, the Malfunction Indicator Lamp (MIL) in the instrument panel stays on. If the MIL remains off, check the bulb in the MIL.



Diagnostic Test Mode
A test of the Electronic Engine Control (EEC) system is conducted with power applied. A diagnostic trouble code is indicated by the number of flashes of the Malfunction Indicator Lamp, or by the failed component name and code number on the Rotunda NGS Scan Tool 007-00500.


Heated Oxygen Sensor Monitor Test
A test of the condition of the fuel mixture (lean or rich), which is monitored by the heated oxygen sensor, is conducted. The condition is displayed by on and off flashing of the MIL, or by FUEL changing LEAN and RICH (on the NGS Scan Tool screen display) more than 5 times during 10 seconds.


Switch Monitor Test
A test of EEC input switches is performed.