ECM-PROM INCOMPATABILITY- POOR PERFORMANCE

VEHICLES AFFECTED: 1984 Brougham, DeVille, Eldorado, and Seville

A 'Service Now' tell-tale with unusable diagnostics and poor performance may occur on some 1984 HT4100-equipped vehicles after an ECM replacement. This is a result of an incompatibility of some 1984 PROM's with service ECM'S. ECM service part number 1226028 is to be used on all 1983 and 1984 HT4100 equipped vehicles. Some ECM's were mislabeled as service P/N 1226463 rather than 1226028. This mislabeling does not affect the quality or operation of the ECM.

When diagnosing leads to replacing an ECM, the following procedure should be used to determine if an ECM-PROM incompatibility exists.

1. Transfer PROM from original ECM to service ECM.

2. If diagnostics are unusable, the PROM must be replaced. Refer to table below for proper service part number.

3. If a diagnostic code is present after an ECM replacement, the PROM should not be replaced and the Service Manual diagnostic procedures must be followed in the normal manner.

The following service PROM part numbers should be used to service all 1984 HT4100-equipped vehicles. Broadcast Replace Code Broadcast Code Body Emission With Service On OEM PROM Style Calibration Service P/N PROM ----------- ----- ----------- ----------- ---- CAO E/K Federal Digital I.P. 16042066 DMX CAS E/K & E Convertible Federal Digital I.P. 16042000 DLW and Optional Axle CAT E/K Federal Mechanical I.P. 16042069 DMY CAX E/K & E Convertible Federal Mechanical I.P. 16042010 DLZ and Optional Axle CYP E Convertible Federal Mechanical I.P. 16042014 DMA CYR E Convertible Federal Digital I.P. 16042017 DMB CYS E Convertible Calif. Mechanical I.P. 16042020 DMC CYT E Convertible Calif. Digital I.P. 16042024 DMD DBB D Calif. 16042033 DMJ DBC D Export 16042036 DMK DBF E/K Calif. Mechanical I.P. 16042042 DMM DBH E/K Calif. DititalI.P. 16042045 DMN DBJ E/K Export Mechanical I.P. 16042048 DMP DBK E/K Export Digital I.P. 16042051 DMR DBL E/K Swiss Mechanical I.P. 16042054 DMS DBM E/K Swiss Digital I.P. 16042057 DMT DCM D Federal Optional Axle 16042060 DMU D Federal 16042063 DMW

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.