CRUISE CONTROL DISENGAGEMENT WITH BCM CODE B127 STORED. Cadillac Eldorado 1986

MODELS AFFECTED: 1986 ELDORADO AND SEVILLE

Cruise control disengagement, accompanied by a BCM Code B127 (PRND321 sensor circuit), may occur on some 1986 Eldorados and Sevilles. Symptoms experienced may include:

(A) Cruise control disengages while driving, at times when the gear selector is not being moved by the driver. Code B127 is stored as either a current or history code.

(B) Cruise control disengages only if gear selector is moved while driving. Code B127 is stored as a history code.

Code B127 will set if the BCM is unable to detect a valid shift position reading. Valid readings can be checked in BCM diagnostics using the BD41 data parameter values listed in the chart below. An open or short to ground in circuit #356 will cause a zero BD41 value. If the gear shifter is moved too slowly between positions or is mispositioned by the driver, Code B127 can also set.

Gear Shift BCM Data Position Value BD41 -------- ---------- Park 98 to 78 Reverse 75 to 60 Neutral 58 to 44 Drive 42 to 31 3 30 to 21 2 20 to 12 1 12 to 5

If Code B127 is set as a history or current code, refer to Service Information Manual Section 8D2, chart for "B127 PRND321 CIRCUIT" for troubleshooting procedure. Should it be determined that a switch adjustment is necessary, refer to Section 7 in the Service Information Manual.

Moving the gear shift too slowly between selections, or mispositioning the gear shift, can "Induce an intermittent reading at the BCM. Should this situation exist for two seconds, Code B127 will set. A new BCM PROM will be made available to eliminate the susceptibility of setting B127 codes when no PRND321 switch condition exists. A bulletin will be published providing details about the new PROM when it is available. Until this new PROM is available, part replacements are not recommended unless an invalid sensor reading is always present as shown by BCM diagnostic parameter BD41, and/or a current BCM code B127.

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.