Electronic Cruise Circuit '93-04
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The Speed Control Servo/Amplifier Assembly uses a servo motor working through a magnetic clutch to move the throttle through the Actuator cable. Diesel trucks from '94.5-up have no servo - the speed control function is integrated into the PCM.
The Programmable Speedometer/Odometer Module (located in the Instrument Cluster) sends a speed signal to the input of the Speed Control Servo/Amplifier Assembly through the 679 (GY/BK) wire. This signal tells the Amplifier the vehicle's current speed.
To operate the Speed Control System, the ignition switch must be in RUN and vehicle speed must be greater than 30 mph (R/LB & Gy/Bk greater than ~67Hz). The System is turned on by pressing the Speed Control Switch ON. Do not activate the speed control with the transmission, transaxle, or transfer case in NEUTRAL. This could result in the engine over-revving.
Pressing and releasing SET/ACCEL or COAST sends a command to the Speed Control Amplifier. If the system is on but not active, this command makes the vehicle's current speed the set speed.
Pressing and holding SET/ACCEL (LB/Bk ~680ohms to DG/Or) while the system is on and active increases the vehicle's speed as long as SET/ACCEL is depressed. Releasing SET/ACCEL gives the System a new set speed to maintain. Vehicle speed may also be increased by depressing the accelerator until the higher speed is reached, then depressing and releasing SET/ACCEL. Tapping SET/ACCEL while the system is on and active increases set speed by 1mph (1.6kph) per tap.
Pressing and holding COAST (LB/Bk ~120ohms to DG/Or) while the system is on and active decreases the vehicle's speed as long as COAST is depressed. Releasing COAST gives the system a new set speed to maintain. Tapping COAST while the system is on and active reduces set speed by 1mph (1.6kph) per tap down to a minimum of ~30mph.
Pressing OFF turns off the System (LB/Bk shorted to DG/Or). The System is also turned off when the Ignition Switch is turned OFF (Wh/Pu NOT POWERED).
Depressing the brake pedal (Tn/LB greater than 9V to R/LB) cancels the speed controls. The Deactivator Switch also operates (R/LG less than 9V to R/LB) when the brake pedal is depressed. This is a backup device that releases the servo and cancels the system. In vehicles with manual transaxle, the Clutch Switch opens (Tn/LB greater than 5ohms to R/LB) when the clutch pedal is depressed and cancels the system.
When the System has been cancelled by depressing the brake (Tn/LB greater than 9V) or clutch pedal (Tn/LB greater than 5ohms to R/LB), the last set speed may be resumed by pressing RESUME (LB/Bk ~2200ohms to DG/Or). RESUME will not work if OFF has been depressed or with car speed below ~30 mph or if the key has been cycled to OFF since the last system activation.
The cruise servo pins are:
1 - Or/LB - Cruise Set Indicator Lamp Ground Output for 12V incandescent '96 Taurus (or SCP pos)
2 - UNUSED (or SCP neg)
3 - Gy/Bk - VSS input
4 - Tn/LB - BOO & CPP input
5 - LB/Bk - Control Switch Input
6 - Bk - Control Switch Discrete Ground (may not connect to any other circuit)
7 - Wh/Pu - Switched Power
8 - UNUSED
9 - R/LG - Servo Clutch Power (SCCDS) Input
10 - Bk - Ground
NOTE that some diagrams label the pins in reverse, so observe wire colors.
Visual inspection is an important part of diagnosis. When performing visual inspection, check all items for abnormal conditions. Look for such items as bare, broken or disconnected wires. For the speed control to function properly, the servo (throttle actuator) and throttle linkage should operate freely and smoothly. Any concerns found by the visual inspection should be corrected before further tests of the speed control system are made. The following items should be inspected.
- If the amber RABS indicator in the instrument cluster stays lit when the ignition switch is in the RUN position, then refer to servicing the rear anti-lock brake system before continuing with the speed control diagnostics.
- Does the horn work? If not, check the horn circuit fuse, horn relay and horn circuit wiring.
- Do the stoplamps light when the brake pedal is depressed? If not, check the stoplamp circuit fuse, stoplamps, wiring and stoplamp switch.
- Look for loose or unseated speed control servo connector pins.
- Check for broken wires at the connectors.
- Check for speed control servo cable adjustment.
- Check for broken or bound speed control servo cable.
SPEED CONTROL DIAGNOSTICS, GASOLINE ENGINES
Condition: Possible Sources;
Action
Speed Control Inoperative: Blown fuse; Circuitry; Stoplight switch/bulbs; Speed control actuator switch assembly; Deactivator switch; Speed control servo.
GO to Pinpoint Test A .
Set Speed Fluctuates: Programmable Speedometer/Odometer; Speed control servo; Speed control actuator switch assembly; Circuitry; Loose fit or binding between speed control actuator cable and throttle body.
GO to Pinpoint Test B .
Set Speed Fluctuates: Engine.
REFER to Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII. SERVICE engine as required.
Speed Control Does Not Disengage When Brakes Are Applied: Stoplight switch; Speed control servo; Circuitry; Deactivator switch; Binding actuator cable.
GO to Pinpoint Test C .
Speed Control Does Not Disengage When Clutch Is Applied: Circuitry; Clutch Switch.
GO to Pinpoint Test D .
COAST Switch Inoperative: Speed control actuator switch; Speed control servo; Circuitry.
GO to Pinpoint Test E .
SET/ACCEL Switch Inoperative: Speed control actuator switches; Speed control servo; Circuitry.
GO to Pinpoint Test F .
RESUME Switch Inoperative: Speed control actuator switch; Speed control servo; Circuitry.
GO to Pinpoint Test G .
OFF Switch Inoperative: Speed control actuator switch; Speed control servo; Circuitry.
GO to Pinpoint Test H .
Pinpoint Tests
NOTE: For 7.3L DI diesel speed control diagnosis, refer to the Powertrain Control/Emissions Diagnosis Manual OBDI or OBDII .
PINPOINT TESTS
To avoid connector terminal damage, always use test probe adapters. Failure to comply may result in spread terminals and intermittent speed control operations.
PINPOINT TEST A: SPEED CONTROL INOPERATIVE
A1 VERIFY THERE IS POWER TO SPEED CONTROL SERVO
Disconnect harness connector from the speed control servo.
Use Rotunda 73 Digital Multimeter 105-R0051 or equivalent to make the specified measurements at the harness connector.
Use Rotunda Terminal Adapter Kit No. 105-R025A to avoid connector terminal damage.
Key to RUN.
Measure voltage between Pin 7 (B , Circuit 298 ) and Pin 10 (GND, Circuit 901).
Is there battery voltage (12v nom.)?
Yes GO to A3 .
No GO to A2 .
A2 CHECK MODULE GROUND CIRCUIT
Key off.
Measure the resistance between Pin 10 (GND, Circuit 901) and ground point on the chassis.
Is resistance less than 5 ohm?
Yes GND is OK. Power to Module may be open. CHECK fuse 5 in Power Distribution Box and Circuit 298. TEST for normal operation. GO to A3
No REPAIR open in ground Circuit 901. TEST for normal operation.
A3 CHECK FOR STUCK STOPLIGHT SWITCH
With no brakes applied, measure the voltage between Pin 4 (BRK, Circuit 306) and Pin 10 (GND, Circuit 901).
Is the battery voltage (12v nom.)?
Yes Stoplight switch is stuck on. REPLACE stoplight switch.
No Stoplight switch is not stuck on. GO to A4 .
A4 CHECK BRAKE/CLUTCH CIRCUIT GROUND
Key off.
Measure the resistance between Pin 4 (BRK, Circuit 306) and Pin 10 (GND, Circuit 901).
Is resistance less than 20 ohms?
Yes Brake/Clutch input circuit OK. GO to A5 .
No Brake light bulbs blown or brake/clutch circuit open. SERVICE circuit including clutch pedal position switch.
A5 CHECK DEACTIVATOR CIRCUIT (AT MODULE CONNECTOR)
Key off, no brakes applied.
Measure the voltage between Pin 9 (DEACT, Circuit 307) and Pin 10 (GND, Circuit 901).
Is there battery voltage (12v nom.)?
Yes GO to A9 .
No No power from deactivator. GO to A6 .
A6 CHECK DEACTIVATOR SWITCH (AT SWITCH)
Remove body harness connector from deactivator switch.
Measure the resistance between the two pins of the deactivator switch with no brakes applied.
Is resistance less than 1 ohm?
Yes Deactivator switch OK. GO to A7 .
No Deactivator switch defective. REPLACE switch. REPEAT Step A5 .
A7 VERIFY THERE IS POWER AT DEACTIVATOR HARNESS CONNECTOR
Measure voltage between Pin 1 (Circuit 10) of the deactivator switch harness connector and chassis ground.
Is there battery voltage (12v nom.)?
Yes Power at connector OK. GO to A8 .
No SERVICE for blown fuse or open in deactivator switch circuit.
A8 CHECK FOR OPEN CIRCUIT BETWEEN DEACTIVATOR SWITCH AND SERVO
Measure resistance from Pin 2 (Circuit 307) of deactivator switch and Pin 9 (DEACT, Circuit 307) of service assembly of speed control servo.
Is resistance less than 1 ohm?
Yes CHECK for bent or corroded pins on deactivator switch and harness connector. SERVICE as required. REPEAT Step A5 . If connections are serviceable, GO to A9 .
No Open in wire harness. SERVICE as required.
A9 CHECK FOR STUCK COMMAND SWITCHES
Key off.
With no steering wheel switches depressed, measure the resistance between Pin 5 (COMMAND, Circuit 151) and Pin 6 (COMMAND RTN, Circuit 848 ).
Is resistance greater than 3k ohms?
Yes No stuck switches. GO to A10 .
No One of the command switches is stuck. REPLACE switch.
A10 CHECK ON SWITCH OPERATION
Key off.
With steering wheel ON switch depressed, measure voltage between Pin 5 (COMMAND, Circuit 151) and Pin 10 (GND, Circuit 901).
Is there battery voltage (12v nom.)?
Yes ON switch OK. GO to A12 .
No ON switch not functioning. GO to A11 .
A11 CHECK FOR OPEN CIRCUIT IN "ON" SWITCH GROUND
With horn depressed, measure voltage between Pin 6 (Circuit 848 ) and chassis ground.
Is there battery voltage (12v nom.)?
Yes Open circuit between Pin 5 and command switches or inoperative switches. SERVICE as required.
No Open circuit or fuse in horn relay feed or open circuit in switch ground. SERVICE as required. REPEAT Step A10 .
A12 CHECK SET/ACCEL SWITCH OPERATION
Key off.
With the SET/ACCEL switch depressed, measure the resistance between Pin 5 (COMMAND, Circuit 151) and Pin 6 (COMMAND RTN, Circuit 848 ).
Is resistance approximately 680 (640-720) ohms?
Yes Switch is OK. GO to A13 .
No Switch not functioning. REPLACE switch.
A13 CHECK FOR SHORT IN COMMAND SWITCH RETURN CIRCUIT
Measure resistance between Pin 6 (Circuit 848 ) and Pin 10 (GND, Circuit 901).
Is resistance less than 1 ohm?
Yes SERVICE short in Circuit 848.
No Return circuit OK. GO to A14 .
A14 VERIFY SPEED SIGNAL
Operate vehicle by raising the rear wheels. Set speed at 30 mph. Use an AC voltmeter to measure the voltage between Pin 3 (SPEED SIG, Circuit 679) and Pin 10 (GND, Circuit 901).
Is voltage reading 4-5 volts?
Yes Speed signal OK. GO to A15 .
No SERVICE Programmable Speedometer/Odometer. GO to Section 13-01 .
A15 CHECK FOR BROKEN OR BOUND ACTUATOR CABLE
Remove speed control actuator cable from speed control servo. Check for broken speed control actuator by pulling on speed control actuator and noting throttle movement.
Is speed control actuator OK?
Yes REPLACE speed control servo.
No SERVICE speed control actuator cable.
PINPOINT TEST B: SET SPEED FLUCTUATES
B1 CHECK THAT CONDITION OCCURS ONLY WHILE USING SPEED CONTROL
Drive vehicle at the speed in which the condition occurs.
Does the speedometer needle waiver by more than ± 2 mph?
Yes Bad Programmable Speedometer/Odometer Module, RABS speed sensor, or rear axle ring gear. SERVICE as necessary.
No GO to B2 .
B2 CHECK PROGRAMMABLE SPEEDOMETER/ODOMETER MODULE OUTPUT SIGNAL
Check PSOM output signal.
Did PSOM pass output signal test?
Yes GO to B3 .
No SERVICE as required.
B3 CHECK FOR BINDING IN SPEED CONTROL ACTUATOR CABLE AND THROTTLE BODY LINKAGE
Check for binding or sticking of speed control cable or throttle linkage and throttle plate.
Make sure throttle cable bracket and speed control servo bracket are not loose.
Are components OK?
Yes REPLACE speed control servo and VERIFY condition is corrected.
No SERVICE as required.
PINPOINT TEST C: SPEED CONTROL DOES NOT DISENGAGE WHEN BRAKES ARE APPLIED
C1 CHECK FOR BINDS IN SPEED CONTROL ACTUATOR/THROTTLE BODY ATTACHMENT
Disconnect 10-way connector from speed control servo.
Check for binding of speed control actuator cable.
Is speed control actuator cable OK?
Yes GO to C2 .
No SERVICE as required.
C2 CHECK BRAKE SWITCH OPERATION
With brakes applied, measure the voltage between Pin 4 (BRK, Circuit 306) and Pin 10 (GND, Circuit 901).
Is there battery voltage (12v nom.)?
Yes REPLACE speed control servo.
No Switch not functioning. REPLACE or SERVICE.
PINPOINT TEST D: SPEED CONTROL DOES NOT DISENGAGE WHEN CLUTCH IS APPLIED
D1 CHECK CLUTCH CIRCUIT
Key off.
Measure the resistance between Pin 4 (Circuit 306) and Pin 10 (Circuit 901).
Is resistance less than 20 ohms?
Yes Clutch input circuit OK. GO to D2 .
No Clutch circuit open. SERVICE circuit including clutch pedal position switch.
D2 CHECK CLUTCH OPERATION
With clutch pedal applied, measure the voltage between Pin 4 (Circuit 306) and Pin 10 (Circuit 901).
Is there battery voltage (12v nom.)?
Yes REPLACE speed control servo.
No Switch not functioning. REPLACE or SERVICE.
PINPOINT TEST E: COAST SWITCH INOPERATIVE
E1 CHECK COAST SWITCH OPERATION
Disconnect 10-way connector from speed control servo.
Key off.
With COAST switch depressed, measure the resistance between Pin 5 (COMMAND, Circuit 151) and Pin 6 (COMMAND RTN, Circuit 848 ) while rotating steering wheel through full range.
Is resistance approximately 120 (114-126) ohms?
Yes COAST switch OK. GO to E2 .
No REPLACE switch.
E2 CHECK COMMAND SWITCH RETURN CIRCUIT
Measure the resistance between Pin 6 (COMMAND RTN, Circuit 848 ) and Pin 10 (GND, Circuit 901).
Is resistance less than 1 ohm?
Yes Switch return is incorrectly grounded. SERVICE as required.
No REPLACE speed control servo.
PINPOINT TEST F: SET/ACCL SWITCH INOPERATIVE
F1 CHECK SET/ACCL SWITCH OPERATION
Disconnect 10-way connector from speed control servo.
Key off.
With SET/ACCL switch depressed, measure the resistance between Pin 5 (COMMAND, Circuit 151) and Pin 6 (COMMAND RTN, Circuit 848 ) while rotating steering wheel through full range.
Is resistance approximately 680 (646-714) ohms?
Yes SET/ACCL OK. GO to F2 .
No REPLACE switch.
F2 CHECK COMMAND SWITCH RETURN CIRCUIT
Measure the resistance between Pin 6 (COMMAND RTN, Circuit 848 ) and Pin 10 (GND, Circuit 901).
Is resistance less than 1 ohm?
Yes Speed control actuator switch return is incorrectly grounded. SERVICE as required.
No REPLACE speed control servo assembly.
PINPOINT TEST G: RESUME SWITCH INOPERATIVE
G1 CHECK RESUME SWITCH OPERATION
Disconnect 10-way connector from speed control servo.
Key off.
With RESUME switch depressed, measure the resistance between Pin 5 (COMMAND, Circuit 151) and Pin 6 (COMMAND RTN, Circuit 848 ) while rotating steering wheel through full range.
Is resistance approximately 2200 (2090-2310) ohms?
Yes RESUME OK. GO to G2 .
No REPLACE switch.
G2 CHECK COMMAND SWITCH RETURN CIRCUIT
Measure the resistance between Pin 6 (COMMAND RTN, Circuit 848 ) and Pin 10 (GND, Circuit 901).
Is resistance less than 1 ohm?
Yes Switch return is incorrectly grounded.
No SERVICE as required. REPLACE speed control servo.
PINPOINT TEST H: OFF SWITCH INOPERATIVE
H1 CHECK OFF SWITCH OPERATION
Disconnect 10-way connector from speed control servo.
Key off.
With OFF switch depressed, measure the resistance between Pin 5 (COMMAND, Circuit 151) and Pin 6 (COMMAND RTN, Circuit 848 ) while rotating steering wheel through full range.
Is resistance less than 4 ohms?
Yes REPLACE speed control servo.
No OFF switch not functioning. REPLACE switch.
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