P051

PROM Checksum Circuit:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) PROM (Programable Read Only Memory) contains data which is essential in running the engine and transaxle. Codes P051/P108 check the integrity of this data. The PROM data is divided into two halves or sides in the PROM. Code P051 checks one half of this data and Code P108 checks the other half.

The integrity of the data is checked by adding up the data in all locations of the PROM. This is called the checksum. If the checksum does not equal what it should, then the code is set. The checksum is only checked when the ignition is turned "OFF" and if it does not match, the code will set the next time the ignition is turned "ON."

This code can set due to several problems, for example:

- A bad connection between the PCM and PROM.
- Incorrect data in the PCM due to electromagnetic discharge, or a faulty PROM.
- An internal PCM problem.

DIAGNOSTIC PROCEDURE
Check that the PROM is fully inserted in its socket. If OK, replace PROM, clear memory and recheck. If code P051/P108 reappears, replace PCM.

NOTE: To prevent electrostatic discharge damage:

^ Do not touch the PCM connector pins or soldered components on the PCM circuit board.
^ When handling the PROM, do not touch the component leads, and do not remove prom carrier cover or integrated circuit from carrier.