Intermittent Codes VS. Hard Codes

Trouble codes stored in the ECM's memory at any time can either be:
a. A code for malfunctions which are occurring now (a ``hard failure''). This malfunction will cause illumination of the ``Check Engine'' light or one of the ``Service'' telltale lights.
b. A code for any intermittent malfunctions which have occurred within the last 50 ignition switch cycles. These codes will not cause the ``Check Engine'' or ``Service'' telltale lights to be on.
Intermittent codes should be diagnosed by inspecting the connectors.
During any diagnostic interrogation which displays more than one diagnostic code, it is necessary to determine which code is for the ``hard failure'' and which is the intermittent. To make this determination, proceed as follows:
1. Enter diagnostics, read and record stored trouble codes.
2. Clear trouble codes.
3. Exit diagnostics by turning the ignition switch off for 10 seconds.
4. Turn ignition ON, wait 5 seconds, then start engine.
5. Accelerate the engine (to approximately 2000 RPM) for a few seconds.
6. Return to idle.
7. Shift transmission into Drive.
8. Shift to Park.
9. If the ``Check Engine'' light or one of the ``Service'' telltale lights comes ON, enter diagnostics, read and record trouble codes. This will reveal only ``hard failure'' codes. If the light does not come on, then all sorted codes are intermittent. Codes 52 through 67 will not illuminate the ``Check Engine'' or ``Service Telltale'' lights. These codes will be stored until 50 ignition switch cycles have occurred or the diagnostic system has been cleared. They are an indication that a specific condition occurred which the technician should be aware. Many of these codes can be driver induced and a decision must be made whether the code requires further investigation.