B1558

CIRCUIT DESCRIPTION
The module calibrations are stored in the EPROM. When the ignition is first turned ON, the module performs internal tests on the EPROM in order to determine the integrity of its non-volatile memory. The module compares its previously stored checksum with the checksum calculated when the ignition is first turned ON. If the 2 checksums do not match, the module will set B1558 as current.

CONDITIONS FOR SETTING THE DTC
^ The stored checksum does not match the calculated checksum.
^ The condition must occur when the ignition is first turned ON.

ACTION TAKEN WHEN THE DTC SETS
^ A DTC B1558 is stored in the BCM memory.
^ No driver warning message is displayed for this DTC.
^ The BCM uses default values for any memory address in the EPROM that is corrupt.

CONDITIONS FOR CLEARING THE DTC
^ This DTC requires an ignition cycle in order to change from current to history.
^ The module no longer detects an internal memory malfunction (checksum error).
^ A history DTC clears after 50 consecutive ignition cycles if the condition is no longer present.

DIAGNOSTIC AIDS
Since the EPROM cannot be removed from the module and DTC B1558 is an internal module malfunction, the module may need to be replaced.

DIAGNOSTIC AIDS
^ This DTC may be stored as a History DTC with out affecting the operation of the module. If stored only as a History DTC and not retrieved as a current DTC, do not replace the module.
^ If this DTC is retrieved as a Current DTC, replace the module.

TEST

Steps 1-4: