Code Output Format

The EEC system communicates service information through Self-Test service codes. These are two-digit numbers representing Self-Test results. The Self-Test is divided into three specialized tests:

1. Key On Engine Off (KOEO) Self-Test.
2. Engine Running Self-Test.
3. Continuous Self-Test.

The Self-Test is not conclusive by itself, but is used as part of the functional Quick Test diagnostic procedure. The ECA computer stores the Self-Test program in its permanent memory. When activated, it checks the EEC system by testing its memory integrity and processing ability, verifying that various sensors and actuators are connected and operating properly.

The KOEO and Engine Running Self-Tests are functional tests which only detect faults present at the time the test is performed. Continuous Self-Test is on-going and stores information that can be retrieved when the test is run. This test is particularly useful for detecting intermittent problems.

Service codes are transmitted on the Self-Test output (STO) wire found in the Self-Test connector. Codes are in the form of timed pulses which can be read by an analog voltmeter, the "Check Engine" light or the Super Star II tester (or compatible aftermarket "Scan" tool).

"Fast codes" are output prior to regular service codes. These codes contain information identical to regular service codes but are transmitted at 100 times the normal rate. These codes are interpreted by special assembly line equipment. Some voltmeters may detect these codes as a slight meter needle deflection.

KEY ON ENGINE OFF (KOEO) AND CONTINUOUS MEMORY CODES

Code Format - KOEO And Continuous Memory Codes:

ENGINE RUNNING CODES

Code Format - Engine Running Codes:

CONTINUOUS MEMORY CODES

Code Format - Continuous Memory Codes:

Continuous Memory codes are separated from KOEO codes by a single separator pulse and are only displayed following KOEO codes. Continuous Memory codes are issued as a result of information stored during continuous Self-Test, while the vehicle was in normal operation. During this mode, the ECA computer continuously monitors inputs for opens and shorts. Continuous Memory codes must be retrieved within 40 engine temperature warm-up cycles. On the 41st cycle, code(s) are automatically erased. Continuous Memory codes can be erased by deactivating Self-Test while service codes are being displayed.

ENGINE I.D. CODES

Engine I.D. codes issued at the beginning of Engine Running Self-Test are one-digit numbers represented by the number of pulses displayed. The code is equal to half the number of engine cylinders (3 pulses equals 6 cylinders). These codes verify that the proper processor is installed and that Self-Test has been entered.

NOTE: The brake pedal MUST be depressed and released AFTER the I.D. code has been displayed. This tests the ability of the EEC system to detect a change of state in the brake "ON/OFF" switch.

DYNAMIC RESPONSE CHECK

The Dynamic Response check verifies movement of TP and MAF sensors during the brief wide open throttle (WOT) performed during the Engine Running Self-Test. The signal for the operator to perform the brief WOT is a single pulse or code 10 on the Super Star II tester.

NOTE: Some vehicles may not display the Dynamic Response signal.