For 1990-2009 cars

# NEW SERVICE PROM TO IMPROVE SHIFT PLEASABILITY

#### MODELS AFFECTED: 1985 FRONT WHEEL DRIVE DEVILLES AND FLEETWOODS EQUIPPED WITH HT4100 ENGINE

New ECM PROMs have been released for 1985 Front Wheel Drive Devilles and Fleetwoods equipped with the HT4100 engine. The PROMs were introduced as a running change to production at VIN Broadcast 314310 at the same time as the change to the new "AM" transmission calibration. The new PROMs can be installed in any 1985 Front Wheel Drive "C" car with an HT4100 engine, regardless of transmission calibration. All part orders for 85 "C" ECM service PROMs are being superseded to the new service PROM part numbers.

The new PROM part numbers are as follows:

NEW PROM SUPERSEDES B.C. Serv. P/N PROM I.D. B.C. Code Serv. P/N PROM I.D. Code --------- --------- --------- --------- --------- ---- "C" Federal, 16052276 215 HMC 16043718 214 DSM "C" Limo/Comm Chassis, National "C" California 16052282 226 HMD 16043724 225 DSN

The new PROM calibration includes:

1. New test conditions for code E13. The old PROM could possibly set a false code E13 intermittently after a warm engine restart. The new PROM will improve the test for code E 13 in all 1985 "C" vehicles, to prevent false code E 13.

2. Improved driveability during acceleration maneuvers. The new PROM provides a richer air-fuel mixture during some accelerations for improved transmission upshift feel. Fuel control is revised to minimize the possibility of a sag being felt after the 1-2 upshift. Changes were also made to reduce the possibility of a bump which may have been noticed as the throttle is opened after an extended downhill coast.

If the transmission is being updated to the "AM" calibration either by: A) modifying an "AY" transmission per Serviceman Bulletin 85-53, or B) by installing an exchange "AM" transmission, the PROM should be updated to the HMC or HMD calibration. Check the PROM I.D. parameter P.1.3. If the PROM I.D. is 215 or 226, the PROM is an HMC or HMD, DO NOT replace the PROM. If the PROM I.D. is other than a 215 or 226, install the appropriate new PROM.

#### Note: A vehicle serviced with a retrofit "AM" transmission calibration prior to the new PROM release should not exhibit any customer complaint level driveability condition and meets all emissions certification standards. The new PROM is recommended in all additional cases of transmission retrof it to the "AM" calibration only because of the minor driveability improvements which the new PROM provides.

If the vehicle sets code E13 either with or without an accompanying code E45, the PROM should be updated to the HMC or HMD calibration, and the vehicle should then be retested per the DFI System Check Chart in Section 6E of the 1985 FWD Deville and Fleetwood Service Information Manual. Also, see Serviceman Bulletin 85-87, filed in Group 6E to check for proper oxygen sensor ground location.

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.