Diagnostic Check

Diagnostic Connectors:

NOTE: Never connect or disconnect the control unit or any sensors with the ignition "ON" unless specifically instructed to do so by a test procedure. Failure to follow this precaution could result in damage to electronic components.

While there is no specific test for the EFC System control unit, nor does it set a trouble code if a fault occurs in its own circuitry, many of the component tests lead to the control unit if no other problems are detected. However, by entering the self-diagnostic "Read Memory" and "D-Check" modes, it is possible to detect certain control unit malfunctions.

Control unit problems can also result from power supply and ground circuit problems. Therefore, these should be checked as well if a faulty control unit is suspected.

READ MEMORY MODE

1. Connect "Read Memory" connectors, leaving "Test Mode" connectors disconnected.
2. Turn ignition switch "ON."
3. If "Check Engine" light flickers (normal condition), disconnect "Read Memory" connectors and enter "D-Check" mode.
4. If any trouble codes are stored, "Check Engine" light should illuminate and codes will displayed by the oxygen monitor LED lamp on the control unit. Confirm code(s) and proceed to "D-Check" mode.
5. If the light does not illuminate at all, it is not a problem with the self-diagnostic function. A problem in the lamp circuit or control unit is indicated. If installing a new lamp that is known good does not correct the problem, proceed to step #6.
6. Turn ignition switch "OFF" and disconnect "Read Memory" connectors.
7. Disconnect control unit connectors.
8. Turn ignition switch "ON."
9. If "Check Engine" light illuminates, a short in the light circuit harness is indicated. Repair as needed.
10. If "Check Engine" light does not illuminate, replace the control unit.

Specification Codes:

D-CHECK MODE

1. Connect "Test Mode" connectors, leaving "Read Memory" connectors disconnected.
2. Turn ignition switch "ON."
3. "Check Engine" light should illuminate and vehicle specification code should be displayed by the oxygen monitor LED lamp on the control unit. [1]
4. If the specification code does not flash, the control unit should be replaced.
5. Check if specification code coincides with vehicle specifications. If not, measure voltage between ground and the indicated terminal of the control unit connector.
6. If voltage does not coincide with vehicle specifications, repair harness.
7. If voltage does coincide with vehicle specifications, replace control unit.

[1] Specification code is read by observing flash duration of the oxygen monitor LED. Units of ten are 1.2 seconds long and units of 1 are 0.2 seconds. The pause between complete numbers is 1.8 seconds. For example, a specification code of "03" will display three flashes of 0.2 seconds in rapid succession followed by a pause of 1.8 seconds. A code of "30" will display three flashes of 1.2 seconds in succession followed by a pause of 1.8 seconds.