Code P051, Prom Checksum Mismatch

PCM PROM contains data essential in running engine and transaxle. Code P051 checks integrity of this data.

Integrity of this data is checked by adding up the data in all locations of the PROM. The total of this data is referred to as the checksum. Code will set when the checksum does not equal what it should. The checksum is only checked when ignition is turned off and if it does not match, diagnostic trouble code will set next time ignition is turned on.

Trouble codes can also be due to a bad connection between PCM and PROM, incorrect data in PCM due to electromagnetic discharge, faulty PROM, or an internal PCM problem.

NOTE: To prevent electrostatic discharge damage, DO NOT touch PCM and PROM connector pins or soldered components on circuit board. When handling PROM, DO NOT touch component leads and DO NOT remove PROM carrier cover or integrated circuit from carrier.

Ensure PROM is fully inserted in socket. If PROM is fully inserted, replace PROM. Clear memory and retest. If Code P051 resets, replace PCM.

Fig 1: Code P051 Schematic, PROM Checksum Mismatch

Courtesy of GENERAL MOTORS CORP.