Mercury MerCruiser MCM 454 Mag MPI Service Manual page 717

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TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI

Code 51 (1 of 1): Calibration Memory Failure (Non-Scan)

CIRCUIT DESCRIPTION:

This test allows the ECM to check for a calibration failure by comparing the calibration value

to a known value stored in the EEPROM.

This test is also used as a security measure to prevent improper use of calibrations or

changes to these calibrations that may alter the designed function of the EFI system.

TEST DESCRIPTION:

Number(s) below refer to step number(s) on the diagnostic table.

STEP 2: This step checks to see if the fault is present during diagnosis. If present, the ECM

is not functioning correctly and must be replaced.

DIAGNOSTIC AIDS:

An intermittent Code 51 may be caused by a bad cell in the EEPROM that is sensitive to

temperature changes. If Code 51 failed more than once, but is intermittent, replace ECM.

An intermittent problem may be caused by a poor or corroded connection, rubbed through

wire connection, a wire that is broken inside the insulation, or a corroded wire.

Any circuitry that is suspected as causing the intermittent complaint should be thoroughly

checked for backed-out terminals, improper mating, broken locks, improperly formed or

damaged terminals, poor terminal-to-wiring connections, corroded terminals and/or wiring,

or physical damage to the wiring harness. After repairs, clear codes following "Clearing

Codes" at the front of this section. Failure to do so may result in codes not properly being

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Was the "On-Board Diagnostic" (OBD) System

Check Performed?

1. Ignition ON.

2. Clear trouble code using clearing codes

Does code 51 reset?

Faulty is not present at this time. Refer to

"Diagnostic Aids" on facing page.

Replace ECM and verify code does not reset.

SERVICE MANUAL NUMBER 23

90-861326--1 MARCH 1999

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