Cruise Control Diagnostics for '93-up electronic servo system
IF THE IMAGE IS TOO SMALL, click it.
Before checking any of the items in this chart, read this FSA:
The Speed Control Servo/Amplifier Assembly uses a servo motor working through a magnetic clutch to move the throttle through the Actuator cable.
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 (servo pins 10 & 3 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 (servo pin 5 ~680ohms to pin 6) 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.
This 1-MPH-per-press feature is unique to Ford speed control systems. It allows speed to be precisely adjusted without drawing the operator's eyes away from the road. If cruise is set at 55, and the speed limit or traffic increases to 65, the operator can simply tap SET/ACCEL 10 times withOUT taking his eyes off the road, and the system will smoothly accelerate to 65 and hold. The same works for reducing the set speed.
Pressing and holding COAST (servo pin 5 ~120ohms to pin 6) 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 (servo pin 5 shorted to pin 6). The System is also turned off when the Ignition Switch is turned OFF (servo pin 7 NOT POWERED). Depressing the brake pedal (servo pin 4 greater than 9V) cancels the speed controls. The Deactivator Switch also operates (servo pin 9 less than 9V) when the brake pedal is depressed. This is a backup device that releases the servo. In vehicles with manual transaxle, the Clutch Switch opens (servo pin 4 greater than 5ohms to GROUND) when the clutch pedal is depressed and cancels the System.
When the System has been cancelled by depressing the brake (servo pin 4 greater than 9V) or clutch pedal (servo pin 4 greater than 5ohms to GROUND), the last set speed may be resumed by pressing RESUME (servo pin 5 ~2200ohms to pin 6). 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 - Cruise Set Indicator Lamp Ground Output for 12V incandescent (or SCP pos)
2 - UNUSED (or SCP neg)
3 - Gy/Bk - VSS input
4 - LG - 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
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.
DIAGNOSTIC STEP DESCRIPTIONS: (details at this link
A1: VERIFY THERE IS POWER TO SERVO
A2: CHECK FOR STUCK BRAKE SWITCH
A3: CHECK BRAKE/CLUTCH CIRCUIT
A4: CHECK DEACTIVATOR CIRCUIT
A5: CHECK FOR STUCK ON SWITCH
A6: CHECK DEACTIVATOR SWITCH CIRCUIT
A7: CHECK FOR STUCK COMMAND SWITCHES
A8: CHECK SET/ACCEL SWITCH OPERATION
A9: VERIFY SPEED SIGNAL
A10: CHECK FOR BROKEN OR BOUND ACTUATOR CABLE
B1: MAKE SURE STEP A3 HAS BEEN DONE
B2: CHECK IGNITION CIRCUIT
B3: CHECK MODULE GROUND CIRCUIT
C1: MAKE SURE STEP A4 HAS BEEN DONE
C2: VERIFY POWER AT DEACTIVATOR SWITCH HARNESS CONNECTOR
C3: CHECK FOR OPEN CIRCUIT BETWEEN DEACTIVATOR SWITCH AND SPEED CONTROL SERVO
D1: CHECK FOR OPEN CIRCUIT IN SWITCH GROUND
E1: CHECK FOR BINDING IN ACTUATOR CABLE/THROTTLE BODY LINKAGE
F1: CHECK "COAST" SWITCH OPERATION
F2: CHECK COMMAND SWITCH RETURN CIRCUIT
G2: CHECK "ACCEL/TAP-UP" SWITCH OPERATION
G3: CHECK COMMAND SWITCH RETURN CIRCUIT
H2: CHECK RESUME SWITCH OPERATION
H3: CHECK COMMAND SWITCH RETURN CIRCUIT
J2: CHECK FOR BINDS IN ACTUATOR CABLE/THROTTLE BODY ATTACHMENT
J3: CHECK BRAKE SWITCH OPERATION
K2: CHECK OFF SWITCH OPERATION
This is the servo for this system:
This is a disassembled clock spring:
For vehicles with a "CRUISE" indicator lamp, this procedure may reveal fault codes:
This test is a key on engine off (KOEO) test only that is conducted in park only with emergency brake fully engaged.
1. Enter self-test diagnostics by depressing the speed control OFF switch while turning the ignition key ON, making sure the engine does not start and is not running. The speed control indicator on the instrument panel will flash once to indicate that speed control module entered the diagnostic mode. Five additional flashes at this point indicate a defective speed control servo. Release the OFF switch.
2. Press the remaining switches in this sequence: ON, RESUME, COAST and SET/ACCEL.
If the ON switch is not depressed within five seconds after entering the diagnostics mode, the module times out and the procedure must be started over.
The speed control indicator lamp will flash as each switch is depressed. Press each switch in the sequence immediately after the indicator light goes out for the previous switch.
There will be a slight delay when the last button is pressed and the lamp flashes.
3. A lamp flash with the last button (SET/ACCEL) indicates that the static test passed. If the lamp does not flash with the last button and there are no additional flashes of the lamp, the switch is defective.
If the lamp does not flash with the last button, and additional flashes occur, follow the chart below for trouble codes:
-- 2 flashes - BPP defective, circuit is defective, brake applied, CPP switch or jumper (if equipped).
-- 3 flashes - deactivator switch is open or circuit defective.
-- 4 flashes - vehicle speed signal is out of range or circuit is defective
4. Immediately (.25 second delay) after the static test, the speed control servo does a dynamic test by automatically actuating the throttle lever from 8 mm (0.315 in) to 12 mm (0.472 in) of travel from the idle position. During the dynamic throttle pull, observe throttle movement to witness any binding or sticking of the speed control cable and correct connection of speed control cable to throttle lever. Make sure the throttle returns to the idle position.
For vacuum cruise troubleshooting ('92-back F-series & Bronco), see this: