PROM - Programmable Read Only Memory: Service and Repair

Calibration Unit (PROM) Socket Location:

ECM Unit:

NOTE: The calibration unit (PROM) is located inside the ECM, and is a replaceable assembly that plugs into a socket. The PROM and socket each have a mark on one end, that must be aligned when installing and care must be used to avoid bending the pin contacts on the PROM.

1. Remove ECM as described previously.
2. Remove access cover retaining screw and cover.
3. Remove extraction/insertion tools provided with replacement tang under unit with slight side to side rocking motion. Remove tool; do not attempt to remove unit at this point.

Calibration Unit (PROM) Removal:

4. At reference end of unit, push extraction tang firmly under unit. Make sure that tang is completely under unit, and above the mating socket.
5. Grasp unit firmly and remove by pulling upward.
6. Compare replacement unit part number with that of unit being replaced to make sure they are the same.

Calibration Unit (PROM) Installation:

7. Press insertion tool down firmly on Unit with painted reference stripe visible.
8. Locate reference end of socket on ECM circuit board. Reference end has small "U2" imprinted on circuit board.
9. With insertion tool, mate unit with socket on circuit board. Make sure reference ends of both units and socket are aligned.
10. With insertion tool unit and socket squarely aligned, push with firm downward pressure until Unit seats.
11. Remove insertion tool and check unit for bent pins, proper seat in socket and alignment.
12. Install access cover and retaining screw.
13. Install ECM and reconnect connectors.
14. Start engine and observe "Check Carb" display. If it is not illuminated, unit is installed correctly and system is functioning properly. If display is illuminated, round trouble code test lead and check or trouble code 51. If this occurs, unit either not fully seated, installed backwards, has bent pins or is defective. Repair as necessary.

CAUTION: If trouble code 51 was caused by calibration unit installed backwards, it must be replaced. Whenever the calibration unit is installed backwards and the ignition turned on, the unit is damaged.