Mem-Cal Unit
To allow one PCM to be used for many different cars, a device called a Memory-Calibration unit or MEM-CAL is used. The MEM-CAL is located inside PCM, and has calibration information based on vehicle's weight, engine, transmission, axle ratio, and several other factors. See Fig 1 . While one PCM part number can be used by many car lines, MEM-CAL is very specific and must be used for right car. It is very important to check latest parts book and Serviceman Bulletin information for correct part number when replacing MEM-CAL. Parameter ED99 can be used to verify proper PROM I.D.
A PCM used for service (called a Controller) comes without a MEM-CAL. The MEM-CAL from old PCM must be carefully removed and installed in new PCM. If MEM-CAL is missing, it will result in a no start and no run condition, and PCM will not send data to BCM. A current code B334 and a "System Problem" message on DIC will result.
The PCM performs diagnostic function of fuel control system. It can recognize operational problems, alert driver through "Engine Control System fault" telltale, and store a code or codes which identify problem areas to aid technician in making repairs.