How to Use the Diagnostic Readout Box

The diagnostic readout box is connected to a mating connector located in the wiring harness by the right front shock tower.

The features of the diagnostic readout box are as follows:

1. To display readout for fault codes, distributor reference signal, switch tests, detonation sensor, and oxygen system operation. The display is used to see five items:
a. DISPLAY CHECK-When the ignition switch is turned on-off-on-off-on code 88 will appear for a few seconds indicating a good display, the on board diagnostics are functioning, and puts the system in the diagnostic mode.
b. FAULT CODES-All fault codes that have been put into memory by the logic module can be seen and recorded.
c. DISTRIBUTOR SIGNAL (REFERENCE PICKUP)-The presence of this signal can be seen on the display when the engine is cranked while in the diagnostic mode. If the display changes 55 to 0 when the engine is cranked, there is a distributor signal. No display change means no signal. Another method of checking for a distributor reference signal is to disconnect and reconnect the battery. Crank the engine and if code 11 appears during the diagnostic mode, there is no reference signal.
d. SWITCH TEST-When a switch is turned on, display should change to 88. When switch is turned off display should change to 00.
e. OXYGEN FEEDBACK SYSTEM-When the diagnostic readout box is connected while the engine is running at operating temperature, the display will show you if the oxygen system is switching (lean-rich) by alternately displaying 0 and 1 (0=lean, 1=rich).
f. DETONATION SENSOR SYSTEM-When the diagnostic readout box is connected while the engine is running, the display will show you if the detonation sensor is operating by displaying 8 when it is retarding ignition timing because spark knock is occurring. The 8 will appear along with the oxygen system switching 0 and 1.

2. HOLD BUTTON-When the button is moved to the "hold" position fault code display will stop and when returned to the "read" position fault code display will continue. This is useful in giving time to record any codes. The button will not hold any other display functions.

3. An actuation test button for checking system functions when required. The "actuator test mode" (ATM) button on the diagnostic readout box, when pressed will ground the auto-shutdown relay and allows the service technician to observe the following test sequence during the diagnostic mode.
a. 3 Sparks from the ignition system.
b. 2 Automatic idle speed motor movements (1 open, 1 close).
c. Electrical function of each bank of injectors. NOTE: In addition to pressing the ATM button the following must be done:
Disconnect the sync. pickup connector at the distributor.
Connect one end of a jumper wire to the tan/yellow wire terminal of the wiring harness connector.
While holding the ATM button down, touch the black/light blue wire terminal of the wiring harness connector with other end of jumper wire.
When the terminal is touched with the jumper wire you should hear one bank of injectors click. When the jumper wire is removed from the terminal you should hear the other bank of injectors click.
As long as the button is pressed, the test sequence will repeat itself. However the logic module will turn off the ATM "capability" 5 minutes after the ignition switch is turned on.

IMPORTANT-When the actuator test button is pressed fault code #42 is generated. Do not use this code as part of any diagnostic sequence after pressing the button.