DFI ECM CHANGE AND PROM DIAGNOSIS

DFI ECM Change

Production of 1981 DFI equipped cars is being changed from a first generation ECM to a mccon4 generation ECM with greater diagnostic capability. This change will require proper ECM identification prior to service replacement of either the ECM or the PROM. First generation ECM's and PROM's must be serviced only with replacement parts specifically listed for use on first generation cars. Likewise, vehicles using second generation ECM's and PROM's can only be serviced with second generation replacement parts. In other words, first and second generation ECM's and PROM's are not interchangeable.

The Table of DFI Parts Usage shown on the reverse side summarizes the various part changes related to different vehicle configurations. Note that in going from first to second generation ECM's, the E/K-FED (49 states) required a throttle body change and the C-CALIF required an EGR valve change. Minimum air adjustments depend an which throttle body part number is used on a given car as outlined in Serviceman Bulletin 81-5 (Group 6C, No. 16).

PROM Diagnosis (Failed or Improperly Seated PROM)

First generation ECM's do not have the diagnostic ability to recognize an improperly seated PROM and cannot set a Code 51. Without this ability, it is difficult to diagnose improper PROM installation. Some symptoms which have been encountered with poorly seated PROM's include diagnostics display of several false codes which will not clear, erratic cycling of various lights and components, or a "hard" back-up condition (See below).

"Hard" back-up differs from the failsoft modes normally provided for various trouble codes. For example, a trouble code for an inoperative component will normally substitute an average value reading for the input of the inoperative component to allow the vehicle to continue running. This is termed a fail- soft condition. Most of the other engine systems will continue to operate normally. In "hard" back-up, however, all engine systems are ignored by the ECM except for the coolant temperature and MAP signals which determine fuel supply and the distributor reference signal which is used for base ignition timing. In "hard" back-up:

the check engine light will be lit,

no coolant light illumination st ignition on, (engine not running)

no ISC operation,

no MPG display

no diagnostic display (".." displayed only).

Second generation ECM's have the ability to check certain installation con- ditions of the PROM's and will, in most cases, display a code 51 if a PROM is improperly seated. Nevertheless, technicians should be aware that some installation conditions even on second generation ECM's are not checked by the ECM and will not set a Code 51. In cases where Code 51 is not displayed and any of the above described symptoms of improper PROM installation are apparent, both PROM's should be checked for proper seating.

the symptoms related to improer PROM installation could also occur if a mismatch exists between ECM and PROM's.

Do not install a first generation PROM in a second generation ECM or a second generation PROM in a first generation ECM.

1981 PRODUCTION ECM AND PROM USAGE CHART

(49 STATE) (49 STATE) MODEL C-FEDERAL C-CALIF E/K-FEDERAL ----- --------- ------- ----------- ECM GENERATION 1 2 1 2 1 2 (Originally Installed in Production 100001 After Breakpoint E-600001 E-After Through 130880 Not Available Through 61866 Breakpoints 130880 616866 K-After K-680001 690461 Through 690461

ECMProduction Number 16012906 16015436 1601666 16015496 16010286 16015426

ECM Service Part Number 1224760 1225120 1224760 1225120 1224760 1225120

PROM I.D. Numbers PROM #1 794SFS 7069KD 6965LW 708SKK 2068BH 7067KC PROM #2 7949FS 707OKD 6967LW 7086KK 2933BH 7068KC

PROM Service Kit Number 1224763 1225122 1224767 1225124 1224764 1225121

Throttle Body Prod Number 17081030 17081030 17081030 17081030 17081033 17081031

Throttle Body Service Number 17067142 17067142 17067142 17067142 17068019 17067144

EGR Valve Prod. Number 17064905 17064905 17064905 17075769 17064906 17064906

EGR Valve Service Number 17067107 17067107 17067107 N/A 17067108 17067108

MODEL E/K CALIF D-FED ----- --------- ----- ECM GENERATION 1 2 2 (Originally Installed in Production E-600001 E-Mter After Through 617927 130880 Breakpoints 617927 X-Mter K-680001 691350 Through 691350

ECMProduction Number 16015416 16015486 16016926

ECM Service Part Number 1224760 1225120 1225120

PROM I.D. Numbers PROM #1 7013KB 7079KJ 7087LY PROM #2 7014KB 708OKJ 7088LY

PROM Service Kit Number 1224765 1225123 1225125

Throttle Body Prod Number 17081031 17081031 17081030

Throttle Body Service Number 17067144 17067144 17067142

EGR Valve Prod. Number 17064908 17064908 17064909

EGR Valve Service Number 17067110 17067110 17067111

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.