Reading Diagnostic Trouble Codes

The check engine lamp on the instrument panel will illuminate if the logic module or SMEC receives an incorrect signal or no signal from the coolant temperature sensor, charge temperature sensor, MAP sensor, throttle position sensor or battery voltage sensor input depending on vehicle application. This lamp indicates that the logic module or SMEC has gone into the ``limp in mode'' to keep the system operational, and indicates an immediate need for service.

The check engine lamp has two modes of operation. They are as follows:

1. DIAGNOSTIC MODE - If for some reason the DRB II is not available, the SMEC can show you fault codes by means of flashing the check engine lamp on the instrument cluster.

NOTE: In most cases proper diagnostics cannot be determined by only using fault codes. Remember they are only the result, not necessarily the reason for the problem.

To activate this function turn the ignition key on-off-on-off-on within five seconds. The check engine lamp will then come on for two seconds as a bulb check. Immediately following this it will display a fault code by flashing on and off. There is a short pause between flashes and a longer pause between digits. All codes displayed are two digit numbers with a four second pause between codes.

An example of a code is as follows.
a. Lamp on for two seconds, then turns off.
b. Lamp flashes five times, pauses, then flashes once.
c. Lamp pauses for four seconds, flashes five times, pauses and then flashes five times.
The two codes are 51 and 55. Any number of codes can be displayed as long as they are in memory. The lamp will flash until all of them are displayed.

2. SWITCH TEST MODE - After all codes are displayed, switch function can be verified. The lamp will turn on or off when a switch is turned on or off.