Code P051 & P108, Prom Checksum Mismatch

PCM PROM contains data essential in running engine and transaxle. Codes P051 and P108 checks the integrity of this data. RPM is divided into 2 halves or sides in the PROM. Code P051 checks one half of this data and Code P108 checks the other half. Integrity of this data is checked by adding up the data in all locations of the PROM, called the checksum. If checksum does not equal to what it should, code is set. The checksum is only checked when ignition is turned off and if it does not match, 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 internal PCM problem.

NOTE: To prevent electrostatic discharge damage, DO NOT touch PCM and PROM connector pins or soldered components on circuit board.

Ensure PROM is fully inserted in socket. If PROM is fully inserted, replace PROM. Clear memory and recheck. If Code P051 or P108 reappears, replace PCM.

Fig 1: Code P051 & P108 Schematic (4.6L)

Courtesy of GENERAL MOTORS CORP.