Cruise Control System Cadillac Brougham I

DESCRIPTION

The cruise control system uses vacuum to actuate a throttle power unit or servo. Servo moves throttle when it's diaphragm is subject to varying amounts of vacuum. Vacuum to servo is constantly modulated in response to commands from Electronic Control Module (ECM) or cruise control electronic controller.

The ECM or cruise control electronic controller receives data from the engagement, instrument panel switches, electric brake release switch and speed sensor. A 2-position switch ("ON" and "OFF"), located on instrument panel and engagement switches on turn signal lever or steering wheel switches, control system operations.

There are 2 methods for brake release of cruise control: an electric switch and a vacuum valve. Both switches are mounted on brake pedal. Both switches vent servo diaphragm vacuum to atmosphere.

Components used in cruise control system varies depending on vehicle model. Use OPERATION in this article as a guide to determine component application of vehicle being serviced. Controls on Brougham, DeVille and Fleetwood are on turn signal lever. Controls on Eldorado and Seville are on steering wheel and dash panel.

Brougham

Cruise control module receives signals from cruise engagement switch, instrument panel switch, electric brake release switch, servo position sensor and speed sensor circuit. Cruise control module processes this information and transmits command signals to vacuum and vent valves in the servo, to control vehicle speed.

DeVille, Eldorado, Fleetwood & Seville

ECM receives input signals from engagement switches, instrument panel switch, brake release switch and speed sensor. ECM processes cruise control information along with DFI engine control information and transmits command signals to servo for opening or closing of its vent valve and/or vacuum valve to control vehicle speed.

Speed sensor is located behind speedometer cluster. It provides a signal corresponding with vehicle speed to the control system. A speed sensor circuit wire harness connects speed sensor to a buffer amplifier, located behind left side of instrument panel. A buffered speed signal is sent to the electronic controller, via instrument panel wiring harness and cruise control wiring harness.

The speed sensor consists of a Light Emitting Diode (LED) and photo transistor, enclosed in one housing. Photo transistor generates an electrical signal corresponding to vehicle speed when exposed to reflected light from LED.

DeVille & Fleetwood

Speed sensor is driven directly by transaxle. Output of speed sensor is a low-voltage signal whose frequency is proportional to vehicle speed. A speed sensor buffer amplifier shapes and amplifies signal before it is sent to ECM.

Eldorado & Seville

Speed sensor consists of a Permanent Magnet (PM) generator that is driven directly by transaxle. Output of PM generator is a signal with a repetition rate of 4000 pulses per mile. Signal frequency is proportional to vehicle speed and cycles at the rate of 1.1 Hz/MPH.

Voltage generated will vary between .5 and 40 volts. Output of speed sensor is routed to Body Computer Module (BCM). Vehicle speed information is sent from BCM to ECM on the ECM speed sensor input circuit. BCM is only involved with speed sensor which can generate a test Code B124.

Brougham, Eldorado & Seville

Servo operates throttle in response to signals from ECM or electronic controller. The servo uses a vacuum operated diaphragm. A normally open solenoid valve vents the diaphragm chamber to atmosphere. A normally closed solenoid valve connects diaphragm chamber to vacuum source.

Servo unit is a vacuum actuated variable position diaphragm assembly that positions throttle when system is operating. It operates throttle via a cable or rod actuator. When vacuum is applied to evacuate the servo, atmospheric pressure applies force to the diaphragm and moves the diaphragm inward, pulling on actuator to open throttle. The servo does not utilize externally servo-mounted valves. Servo functions for various speed conditions are steady speed, vehicle losing speed and vehicle gaining speed.

When cruise control is on and engaged (without new input from control switches), speed correction operations occur when vehicle speed varies from set cruise speed by about +/- 1/4 MPH. Servo unit also goes to an open vent valve mode when brake pedal is depressed, cruise control system loses electrical power or when ignition is turned off.

Throttle Position Sensor (TPS) is an integral part of DFI system. TPS is monitored to provide feedback to ECM. ECM compares the TPS to vehicle speed signal and makes corrections to the vent and vacuum solenoid control to provide best possible speed control.

INSTRUMENT PANEL SWITCH

The instrument panel switch must be in the "ON" position for system to operate. An Amber light will be on when system may be engaged. Vehicle may enter cruise control mode at any speed over 25 mph.

On Eldorado and Seville, when system is engaged, the "CRUISE CONTROL ENGAGED" light will come on. On Brougham, DeVille and Fleetwood, a Green light will illuminate next to word "ENGAGED" or "AUTO", when system is engaged.

If set/coast button switch is depressed as ignition is turned on, an ECM 067 test code will be set and cruise control will remain inoperative until ignition switch is cycled.

If R/A switch is held in "ACCEL" position while ignition is turned on, ECM 067 test code will be set and cruise control will remain inoperative until ignition switch is cycled.

Engagement switch is a push button switch located at end of turn signal lever, with various modes of operation. Instrument panel switch must be in the "ON" position. With desired speed obtained, momentarily press engagement switch to activate cruise control system. This will set speed at which the vehicle is traveling. The ECM will provide a signal to servo unit to regulate vacuum required to maintain speed.

If decrease in speed is desired, fully depress and hold push button. When push button is released, vehicle will cruise at new lower speed. If set speed is desired to be decreased by only a couple of MPH, the driver can momentarily depress button. Each quick tap of push button will decrease set speed by one MPH.

ELECTRIC BRAKE RELEASE SWITCH & VACUUM RELEASE VALVE

1. Check adjustment of brake release switch and vacuum release valve by measuring brake pedal travel distance. Cruise control switch contacts should open at .137-.492" (3.5-12.5 mm) of brake pedal travel, measured at centerline of brake pedal pad. Nominal actuation of stoplight switch contact is .177" (4.5 mm) after cruise control contacts open.
2. Vacuum release valve assembly should open at 1.06-1.30" (27-33 mm) of brake pedal travel, measured at centerline of brake pedal pad.

ROAD TEST

Note. For trouble code testing information, refer to appropriate article in the COMPUTER ENG CONTROL for diagnosis.

1. With instrument panel control switch in "OFF" position, drive vehicle at 50 MPH. Depress and release engagement push button at end of turn signal lever. System should remain inoperative.
2. Place instrument panel switch in "ON" position. Amber indicator light should be on. Engage system by momentarily pushing turn signal engagement push button and releasing at 50 MPH. Remove foot from accelerator. Green light should be on and vehicle should maintain 50 MPH with foot off accelerator.
3. Push slide switch and hold. Vehicle should accelerate at a controlled rate. Release switch at approximately 55 MPH. Speed should remain steady at 55 MPH. Depress brake pedal about 1/2". If Green light goes off, electric brake switch is okay and vehicle speed should decrease.
4. Allow vehicle to decrease to approximately 45 MPH. Momentarily push slide switch and release. Vehicle should accelerate to 55 MPH at a controlled rate and Green light should be on.
5. Push and hold engagement button. Green light should go off. Coast to 50 MPH and release button to engage system at 50 MPH. Green light should be on and vehicle should maintain speed.
6. Check "tap-up" feature by actuating slide switch for less than a second. Vehicle should increase speed by approximately one MPH. Tap switch a couple more times to check incremental speed increases.

On-Vehicle

1. Turn ignition and instrument panel switch on. Connect test light or voltmeter to ground. Probe Brown wire (Brougham) or Purple wire (except Brougham) at brake switch connector with test light or voltmeter.
2. If test light is on or voltmeter shows 12 volts, system is okay. If test light is not on or 12 volts are not present, probe adjacent terminal. If test light is on or 12 volts are present, adjust or replace switch as necessary. If test light is not on or 12 volts are not present, repair wiring to switch.

INSTRUMENT PANEL & ENGAGEMENT SWITCHES (BROUGHAM)

Note. The following component testing procedures are for Brougham models only. Testing information for all other models is not available from manufacturer.

1. Turn ignition on. Connect test light or voltmeter to ground. Probe the 3 terminals of turn signal lever cruise control harness connector, first with instrument panel switch in "OFF" position, then in "ON" position.
2. There should be no power to any terminal with switch off. With switch on, there should be no power to Blue and Gray wire terminals. There should be power to Brown wire center terminal. The Amber indicator light should also be on.
3. Probe Gray wire terminal and depress set/coast switch. Power should be present. Probe Blue terminal and depress resume/accel switch. Power should be present. Replace turn signal lever switch if power is not present.

AMBER "ON" LIGHT INOPERATIVE (BROUGHAM)

1. Turn ignition on. Place instrument panel switch in "ON" position. If Amber light is not on, check bulb and replace if necessary. If bulb is okay, check for open ground wire, open connector, inoperative switch, blown fuse or defective printed circuit.
2. Turn instrument panel switch to "OFF" position. If Amber light is on, check for shorted leads and/or defective switch.

GREEN "CRUISE" LIGHT INOPERATIVE (BROUGHAM)

1. Perform road test. If road test indicates cruise control system functions properly and Green light is inoperative, check bulb and replace as necessary. If bulb is okay, check for open in Pink wire between switch and controller connector and for defective controller.
2. With instrument panel switch on and ignition on, ground Pink wire in controller. Green light should be on. If Green light is on but not during road test, replace controller.
3. If Green light remains on when system is not controlling speed, check for short in harness between switch and controller connector. If no short is present, replace controller.

TROUBLE SHOOTING

Faulty operation can be caused by one or more mechanical, electrical and/or vacuum problems. before performing diagnosis, make a visual inspection for disconnected or damaged wiring. Check for pinched, cracked, plugged, loose or disconnected vacuum hoses and ensure linkage is not binding or misadjusted. Repair or adjust as necessary.

1. If "tap-up" and "tap-down" functions are the only system faults, replace cruise control module. Check resistance between grounds on cruise control servo and cruise control switch. If resistance is greater than 0.1 ohm, clean and tighten grounds and negative battery cable. If system ground is suspected, install a ground strap between engine block and bulkhead.
2. If using a digital multimeter for testing (Scheme 2) If using a cruise control quick checker for testing (Scheme 3) For symptom checking of cruise control (Scheme 1) For connector identification (Scheme 5)

Scheme 1

Scheme 2

Scheme 3

Scheme 4

Scheme 5

Use the diagnostic chart for speed sensor system. (Scheme 6)

Scheme 6

Use the flow chart to test cruise control servo. (Scheme 7)

Scheme 7

Scheme 8

Removal & Installation

Disconnect electrical connector and vacuum hoses from servo unit. Remove servo cable from servo unit and remove servo unit. Install servo unit and tighten nuts to 12 INCH lbs. (1.4 N.m). Install servo unit cable, vacuum hoses and electrical connector.

1. Ensure engine is off. Remove retaining clips from each end of cruise control cable. Remove accelerator cable and cruise control cable from throttle lever. Separate accelerator cable and cruise control cable. Carefully remove cable without disrupting throttle valve cable, spark plug wires and accelerator cable.
2. Route cruise control cable under spark plug wires, throttle valve cable and accelerator cable. Retract idle speed motor until throttle lever is clear of plunger. Attach cruise control cable and accelerator cable to throttle lever. Attach cruise control cable to servo unit, using hole in servo to achieve minimum cable slack.

Removal

Remove left hush panel. Disconnect electrical connector and vacuum hose (if equipped) from valve. Remove attaching screw. Remove valve or switch from dash bracket. (Scheme 8)or (Scheme 9).

Scheme 9

Scheme 10

Installation

1. Hold brake pedal depressed and install switch or valve assembly into retainer. Switch or valve should bottom on retainer. Note that an audible click can be heard as threaded portion of switch is pushed through retainer.
2. Slowly pull brake pedal fully rearward against pedal stop, moving switch or valve assembly rearward. On vehicles equipped with anti-lock brakes, release brake pedal and allow it to come to rest.
3. Release brake pedal and pull back again to assure proper adjustment of switch or valve. On vehicles equipped with anti-lock brakes, slowly push switch or valve further into retainer until plunger is seated against brake pedal bracket. Visually check for proper seat.
4. To complete installation, reverse removal procedure. See ADJUSTMENTS in this article.

SET/COAST & RESUME/ACCEL SWITCHES

Note. Set/coast switch, resume/accel switch or illumination bulbs cannot be replaced separately.

Removal & Installation (Eldorado & Seville)

Remove 2 screws retaining horn pad. Disconnect cruise control switch connector and horn lead. Remove 2 screws attaching horn contact assembly. Remove 3 nuts attaching retainer and switch assembly. Remove resume switch button. Remove trim plate. (Scheme 12) To install, reverse removal procedure.

Scheme 11

ENGAGEMENT SWITCH

Note. Engagement switch is not serviceable. Complete turn signal lever must be replaced.

Removal (DeVille & Fleetwood)

1. Disconnect negative battery cable. Remove steering column access cover. Disconnect cruise control switch harness connector. Do not pull on steering column harness connector more than necessary. Ensure turn signal lever is "NEUTRAL" position.
2. Pull lever out of detented retaining clip inside steering column. Pull harness up and out gently to remove unit. Removal of protective plastic from cruise control wires may ease switch removal.

1. Place transaxle selector in "LOW" position. Place turn signal lever wiring into steering column. Align tang on turn signal lever shaft with notch in switch. Push shaft into switch, pressing on end of lever to seat lever in switch.
2. Gently pull wire at lower end of column, feeding harness into proper location in column. Connect lever harness connector. Install access cover. Reconnect negative battery cable.

Disconnect wiring harness connector from speed sensor. Remove speed sensor retainer clip. Pull speed sensor from governor housing. Remove driven gear and seal. To install, reverse removal procedure.

Removal & Installation (Brougham)

Disconnect negative battery cable. Remove speedometer cluster. Remove clip retaining strap holding buffer amplifier. Disconnect electrical connector and remove buffer amplifier. To install, reverse removal procedure.

Removal & Installation (DeVille & Fleetwood)

Disconnect negative battery cable. Remove right-hand trim panel. Remove glove box assembly. Remove shield and link. Remove programmer and speed buffer assembly. Disconnect electrical connectors and separate buffer from programmer. (Scheme 12) To install, reverse removal procedure. When installing link, set A/C control to max heat and high blower. Pull linkage toward right and reinstall nylon clip.

Scheme 12

Remove instrument panel trim plates. Remove screw retaining switch to panel. Disconnect electrical connector and remove switch. To install, reverse removal procedure.

The cruise control instrument panel switch is mounted in with wiper switch and mirror switch module. Remove instrument panel trim plate. Remove 2 screws retaining switch assembly holder to instrument panel. Disconnect electrical connectors. To install, reverse removal procedure.

WIRING DIAGRAMS

For wiring diagrams, refer to appropriate chassis wiring diagram in WIRING DIAGRAMS section.