Reading Diagnostic Trouble Codes

Diagnostic Procedures

The self-diagnostic system detects the troubles most likely to occur. The diagnostic system illuminates panel when a trouble is detected. When a jumper wire is connected between trouble code TEST terminals 6 and 7 of the 15-terminal diagnostic connector (D-2) the CHECK ENGINE light will flash a trouble code or codes that indicate the trouble area(s).

For bulb and system check, the CHECK ENGINE light will illuminate when the ignition switch is ON and the engine not started. If the TEST terminals are the grounded, the light will flash a code 12 that indicates the self-diagnostic system is operational. A code 12 consist of one flash, followed by a short pause, then two flashes in quick succession. After a longer pause, the code will repeat two (2) more times.

When the engine is started, the CHECK ENGINE light will remain ON momentarily and then be turned off. If the CHECK ENGINE light remains on, the self-diagnostic system has detected a trouble. If the TEST terminals are then grounded, the trouble code will be flashed three (3) times. If more that one trouble has been detected, each trouble code will be flashed three (3) times.

The trouble codes will flash in numeric order (lowest number code first). The trouble code series will repeat as long as the TEST terminals are grounded.

A trouble code indicates a trouble in a particular circuit or component. Trouble Code 14, for example, indicates a trouble in the coolant sensor circuit, this includes the coolant sensor, connector, harness, and the ECM. The procedure for locating the trouble is in Diagnosis Chart No. 14. Similar diagnosis charts are provided for each code.

Because the self-diagnostic system does not detect all possible troubles, the absence of a code does not mean there are no trouble codes in the system. To determine if there is a system trouble, a System Performance Test is necessary. This test is made when the CHECK ENGINE light and self-diagnostic system do not indicate a trouble, but the system i suspected because no other reason can be found for the complaint.