DESCRIPTION
System consists of a multi-function control switch, electronic controller module, servo unit, vacuum reservoir, speed sensor, vacuum supply, electrical and vacuum release switches, and electrical wire harness.
A vacuum operated servo unit is used to maintain desired speed. System controller module monitors vehicle speed and servo position. Controller module operates vacuum and vent valves in servo to maintain or resume desired speed. A low speed limiter (contained within control module) prevents system engagement below 25 MPH.
OPERATION
System operation is controlled by electronic controller module. The electronic controller module monitors vehicle speed through speed sensor. It also monitors operation of multi-function control switch, located on end of turn signal lever and servo position.
Electronic controller module responds to commands from control switch. Controller module controls servo status by holding, increasing or releasing vacuum.
System can be disengaged by turning off cruise control switch or by activating brake or clutch (M/T) release switches. A vacuum release valve controls servo vacuum release to atmosphere as either pedal is depressed.
MULTI-FUNCTION CONTROL SWITCH
Multi-function control switch controls on, off, set speed mode, resume last set speed mode, coast and accelerate modes.
SET/COAST SWITCH
Set/coast switch is located on end of turn signal lever and has 2 positions, normal and depressed.
"SET" Mode
With vehicle speed at or above 25 MPH (cruise control switch in "ON" position), depress and release set/coast switch. Vehicle speed will then be set.
"COAST" Mode
To decrease speed, depress and hold set/coast switch. When vehicle has slowed to desired speed, release switch to set new speed.
"TAP DOWN" Mode
With cruise control engaged and operating, slow vehicle speed by "tapping" set/coast switch. Do not hold switch in depressed position as it will place system in coast mode.
ELECTRONIC CONTROLLER MODULE
Electronic controller module monitors servo position, mode control switches, and output of speed sensor. In response to these input signals, controller module electrically signals opening and closing of vent and vacuum solenoid valves in servo. Controller module is usually mounted on accelerator pedal bracket.
SERVO UNIT
Servo unit consists of an electrically operated vacuum diaphragm. (Scheme 1) Along with a normally open solenoid valve that vents diaphragm chamber to atmosphere, a normally closed solenoid valve that connects diaphragm chamber to vacuum source, and a variable inductance position sensor.
SPEED SENSOR
Vehicle Speed Sensor (VSS) buffer amplifier supplies vehicle speed information to controller module. Optic head portion of VSS is located in speedometer frame. A reflective blade is attached to speedometer cable/head assembly.
As each blade enters LED light beam, causing a low power speed signal to be sent to buffer for signal conditioning. This amplified signal is then sent to controller module.
Scheme 1
VACUUM RELEASE VALVES & VALVE/SWITCHES
These valves or valve/switches are mounted on brake and clutch pedal (M/T) brackets and are used to disengage cruise control whenever clutch or brake pedals are activated.
If pedal is depressed, valve/switches disengage system electrically along with releasing servo vacuum. (Scheme 2) Vacuum release valves, vent trapped vacuum in servo as pedal is depressed, to quickly return throttle to idle position. (Scheme 2)
Scheme 2
BRAKE/RELEASE SWITCH ADJUSTMENT
- With brake pedal in fully released position, brake light plunger should be fully depressed against pedal shank. Adjust switch by moving in or out. Make sure tubular clip is in brake pedal mounting bracket. (Scheme 2)
- With brake pedal depressed, insert switch into tubular clip until switch body seats on clip. (Scheme 2) Audible clicks can be heard as threaded portion of switch is pushed through clip and toward brake pedal.
- Pull brake pedal fully rearward against pedal stop until audible clicking sounds can no longer be heard. Switch will be moved into tubular clip providing adjustment. Release brake pedal and repeat step 3), to make sure that no audible clicking sounds remain.
CLUTCH/RELEASE SWITCH ADJUSTMENT
Position switch slider forward on switch shaft. Fully depress clutch pedal to set switch.
INOPERATIVE ELECTRICAL SYSTEM
Check power supply to electronic controller module terminals "G" and "A". Check for open ground circuits to controller module terminals "J", "H" and servo terminal "C". Check for open leads at or to servo terminals "B" and "D" (servo position sensor).
Check for open leads to or at servo terminals "A" and "E" (vent and vacuum circuits). Check for no high and low voltage signals at module speed sender terminal "D". Check for incorrect input signals to SET/COAST and/or RESUME/ACCELERATE terminals of controller module. Check for poor connections at control module or defective controller module.
INOPERATIVE MECHANICAL SYSTEM
Check for lack of vacuum at small hose to servo. Inspect for mispositioned servo spring and/or rod. Check for leaky servo, broken fittings and/or inoperative valves. Check for disconnected servo linkage. Inspect vacuum release valve for leaks or defective hose.
Electrical
Check for intermittent ground circuits to servo module and/or vehicle speed sensor. Check for intermittent opens in servo position sensor leads, connections and/or terminals. Inspect for voltage surges on positive battery line. Check for turn signal, radio or other electrical component interference. Ensure correct controller module application. Make sure that all vacuum and vent electrical leads are correctly routed.
Mechanical
Check for excess slack in servo linkage. Ensure that servo spring is not sticking. Ensure vacuum release valve is not misadjusted or leaking or hose to valve is not leaking. Check for excessively dry or overlubricated speedometer cable. Make sure that speedometer cable is in good working order.
Check for restricted vacuum supply hose to accumulator or servo. Inspect for binding servo linkage. Check for torque converter clutch cutting in and out or transmission shifting. Check for engine cutting in and out due to mixture or ignition problems. Check that the 3-port or 2-port check valve is positioned properly.
CRUISE SET SPEED HIGH OR LOW
Check vacuum hose routing for pinches, leaks or restrictions. Check servo linkage for excess slack and adjust as described in this article. Check controller module part number to ensure that correct module is in place. Replace controller module, if no system problem is found.
NO RESUME FUNCTION
Ensure that operator is operating system properly. Check for an open connection at terminal "A" of controller module or that terminal is in wrong cavity. Check that controller module is correct one and is operating properly. Inspect for improper operation of multi-function control switch.
UNWANTED CRUISE OR ACCELERATION
Check for crossed vacuum and vent wires. Check for defective or intermittent turn signal control switch. Inspect for sticking valves in servo. Check for binding throttle linkage. Inspect for grease in speedometer head. Check for floor mat interference. Check for loose retainer on bail of servo. Check ground circuit. Ensure that speed sensor is working properly. Check for correct controller module application.
PRELIMINARY INSPECTION
Check system to make sure there are no bare, broken or disconnected wires or any pinched, damaged or disconnected vacuum hoses. Servo and throttle linkage should operate freely and smoothly. Servo linkage should be properly adjusted. If preliminary inspection does not reveal any problems, further testing is required.
CRUISE CONTROL DIAGNOSIS
- Check throttle linkage to servo for adjustment. If not okay, adjust linkage. If adjustment is okay, check electrical and vacuum connections for engagement. Check fuse.
- If connections or fuse are not okay, repair or replace as necessary. If system is okay, perform SERVO RESISTANCE TEST and SERVO VACUUM TEST.
- If servo is okay, perform MULTI-FUNCTION CONTROL SWITCH TEST. If switch is not okay, adjust, repair or replace as necessary. If switch is okay, perform CONTROLLER MODULE VOLTAGE CHECK. If voltage check results are satisfactory, perform CONTROLLER MODULE RESISTANCE CHECK. If resistance check results are okay, but system problems still remain, exchange controller module with known good unit and retest system.
SERVO RESISTANCE TEST
- Turn ignition switch to "OFF" position. Disconnect servo connector and remove servo assembly. Servo terminal pins are labeled by letters "A" through "E". (Scheme 3)
- With an ohmmeter, probe terminal pins "D" to "B" of servo. Resistance should be 15-25 ohms. If resistance is not within specifications, replace servo. If resistance is between 15-25 ohms, go to next step.
- Probe terminal pins "A" to "C" of servo. Resistance should be 30-55 ohms. If resistance is not within specification, replace servo. If resistance is 30-55 ohms go to next step.
- Connect leads between terminal pins "E" and "C" of servo. Resistance should be 30-55 ohms. If resistance is not within specification, replace servo. If resistance is 30-55 ohms, proceed to SERVO VACUUM TEST procedure.
Scheme 3
SERVO VACUUM TEST
- Disconnect linkage from servo to throttle and electrical connector to servo. Start engine and let idle or apply vacuum to servo vacuum port. Manually actuate servo vent and vacuum control valves by connecting jumper wires from battery positive post to pins "A" and "E" on servo assembly.
- Connect another jumper wire between pin "C" of servo and ground. With brake and clutch pedal (M/T) in free position, servo should fully pull in. If servo fails to pull in, check vacuum supply to servo.
- If servo pulls in, remove jumper wire from pin "E" on servo. Servo should stay in position. If servo stays in position, proceed to step 5). If servo fails to remain in position, disconnect vacuum brake release at servo and plug.
- Momentarily reconnect jumper wire to pin "E" until servo fully pulls in, then remove jumper wire. If servo stays in position, adjust or replace vacuum release valve.
- Turn ignition switch to "ON" position. Vacuum release valve should engage. Turn ignition switch to "OFF" position and disconnect vacuum valve connector at valve. Turn ignition switch to "ON" position. With properly adjusted vacuum release switch, battery voltage should be present across connector terminals. No battery voltage indicates an open circuit.
MULTI-FUNCTION CONTROL SWITCH TEST
Using a volt/ohmmeter, test cruise switch at connector terminals mounted on steering column. (Scheme 4)
Scheme 4
CONTROLLER MODULE VOLTAGE CHECK
- With controller module connected, ignition switch in "ON" position, and slider switch in "OFF" position, probe terminal "G" with a voltmeter. With brake/clutch switch not depressed, reading should be 12 volts. With brake/clutch switch depressed, reading should be zero volts.
- Probe terminal "A" with slider switch in "ON" position. Reading should be 12 volts. With slider switch in "OFF" position, reading should be zero volts.
- Probe terminal "M" with slider switch in "R/A" position. Reading should be 12 volts. With slider switch in "ON" position and set/coast button depressed, reading should be zero volts. With slider switch in "OFF" position and set/coast button depressed, reading should be zero volts.
- Probe terminal "L" with slider switch in "ON" position and set/coast button depressed. Reading should be 12 volts. With slider switch in "ON" position and set/coast button not depressed, reading should be zero volts. With slider switch "OFF" and set/coast button not depressed, reading should be zero volts.
- If vehicle is equipped with a cruise control lamp, probe terminal "B" with slider switch in "ON" position and set/coast button depressed. Reading should be 12 volts.
- If vehicle is equipped with a speed sensor, probe terminal "D". Raise and support vehicle. Rotate drive wheels and note voltage output. Voltage should read between 0-4 volts. If not, repair or replace speed sensor.
CONTROLLER MODULE RESISTANCE CHECK
- With controller module disconnected and servo connected, probe terminal "C" to ground with ohmmeter. Reading should be 30-55 ohms. With servo disconnected probe terminal "C" to ground. Reading should be infinity (open circuit).
- With servo connected, probe terminals "F" to "H". Reading should be 15-25 ohms. With servo disconnected, probe terminal "F" to ground. Reading should be infinity (open circuit). With servo disconnected, probe terminal "H" to ground. Reading should be infinity (open circuit).
- With servo connected, probe terminal "K" to ground. Reading should be 30-55 ohms. With servo disconnected, probe terminal "K" to ground. Reading should be infinity (open circuit).
- With servo connected or disconnected, probe terminal "J" to ground. Reading should be infinity (open circuit).
WIRING DIAGRAMS
For wiring diagrams, refer to appropriate chassis wiring diagram in WIRING DIAGRAMS section.