Ford Mustang Service Manual: Speed Control (Diagnosis and Testing)

Ford Mustang Service Manual / Fuel System / Speed Control / Speed Control (Diagnosis and Testing)

Speed Control (Diagnosis and Testing)

Refer to Wiring Diagrams Cell 31 , Speed Control for schematic and connector information.

Special Tool(s)




Worldwide Diagnostic System Worldwide Diagnostic System (WDS) 418-F224, New Generation STAR (NGS) Tester 418-F052, or equivalent diagnostic tool
73 Digital Multimeter or 73 Digital Multimeter or equivalent 105-R0051
Breakout Box, EEC-V Control Breakout Box, EEC-V Control System 418-049, or equivalent 014-00950

Principles of Operation

The speed control system is designed to maintain vehicle speed above 48 km/h (30 mph). After the ON switch is depressed, depressing the SET/ACCEL switch will activate the speed control servo. To increase a set speed, either depress and hold for continuous acceleration, or momentarily tap the SET/ACCEL switch for 1.6 km/h (1 mph) acceleration increments. To decrease a set speed, depress and hold the COAST switch until the target speed is reached, or momentarily tap the COAST switch for 1.6 km/h (1 mph) deceleration increments. When the speed control system has been disabled by tapping the brake pedal, the RESUME switch can be depressed and the vehicle will return to the original set speed if the vehicle is traveling over 48 km/h (30 mph) and the OFF switch has not been depressed.

NOTE: The deactivator switch is provided as an additional safety feature. Normally, when the brake pedal is depressed, an electrical signal from the brake lamp circuit to the speed control servo will deactivate the system. Under increased brake pedal effort, the deactivator switch will open and remove power to the speed control servo, releasing the throttle independent of the speed control servo.

NOTE: The air bag sliding contract provides the electrical interface between the steering column wiring and the speed control actuator switches in the steering wheel.

The inputs to the speed control servo are the:

  • vehicle speed signal.
  • speed control actuator switches.
  • brake pedal position (BPP) switch.
  • clutch pedal position (CPP) switch.
  • deactivator switch.

The output of the speed control servo is the:

  • speed control actuator cable controlling the throttle position.

Inspection and Verification

NOTE: If any concerns are noted with the speedometer, stoplamps, or horn, address those concerns by referring to their associated sections before continuing speed control diagnosis.

1. Verify the customer concern by operating the speed control system.

2. Visually inspect for obvious signs of mechanical and electrical damage.

Visual Inspection Chart

Mechanical Electrical
  • Deactivator switch
  • Speed control actuator cable not attached to throttle
  • Speed control actuator cable not fully seated to the engine bracket
  • Central junction box (CJB) Fuse:
  • 15 (15A)
  • 33 (15A)
  • 35 (15A)
  •  Battery junction box (BJB) fuse:
  • HORN (20A)
  • Wiring harness
  • Loose or corroded connections
  • Speed control actuator switches

3. If the fault is not visually evident, verify the symptom and GO to the Symptom chart.

Symptom Chart

NOTE: New speed control diagnostic software is available in Version 12 or higher for the diagnostic tool. When using this software, it is necessary to use Next Generation Speed Control Adapter 007- 00586 with the diagnostic tool.

NOTE: Refer to the Wiring Diagrams for connector numbers stated in the Pinpoint Test.

Symptom Chart

Condition Possible Sources Action
  • The speed control is inoperative
  • Central junction box (CJB) fuse 17 (15A), 33 (15A).
  • Battery junction box (BJB) fuse HORN (20A).
  • Circuitry.
  • Deactivator switch.
  • Clutch pedal position (CPP) switch.
  • Speed control actuator switch.
  • Speed control servo.
  • Powertrain control module (PCM).
  • Go To Pinpoint Test A .
  • The set speed fluctuates
  • Circuitry.
  • Speed control servo.
  • Powertrain control module (PCM).
  • Engine.
  • Go To Pinpoint Test B .
  • REFER to the Powertrain Control/Emissions Diagnosis (PC/ED) manual.
  • The speed control does not disengage when the brakes are applied
  • Central junction box (CJB) fuse 33 (15A).
  • Circuitry.
  • Brake pedal position (BPP) switch.
  • Speed control servo.
  • Go To Pinpoint Test C .
  • The speed control does not disengage when the clutch is applied
  • Cluch pedal position (CPP) switch.
  • Speed control servo.
  • Go To Pinpoint Test D .
  • The speed control switch is inoperative- COAST
  • Speed control actuator switch.
  • Speed control servo.
  • Go To Pinpoint Test E .
  • The speed control switch is inoperative- SET/ACCEL
  • Speed control actuator switch.
  • Speed control servo.
  • Go To Pinpoint Test F .
  • The speed control switch is inoperative- RESUME
  • Speed control actuator switch.
  • Speed control servo.
  • Go To Pinpoint Test G .
  • The speed control switch is inoperative-OFF
  • Speed control actuator switch.
  • Speed control servo.
  • Go To Pinpoint Test H .

Pinpoint Tests

PINPOINT TEST A: THE SPEED CONTROL IS INOPERATIVE

Test Step Result / Action to Take
A1 CHECK THE SPEED CONTROL SERVO VOLTAGE AND GROUND Yes

GO to A3 .

No

GO to A2 .
  • Key in OFF position.
  • Disconnect: Speed Control Servo C122.
  • Key in ON position.
  • Measure the voltage between speed control servo C122 Pin 7, Circuit 294 (WH/LB), harness side and speed control servo C122 Pin 10, Circuit 1205 (BK), harness side.


  • Is voltage greater than 10 volts?
A2 CHECK THE CIRCUIT 1205 (BK) FOR AN OPEN Yes

REPAIR Circuit 294 (WH/LB). TEST the system for normal operation.

No

REPAIR Circuit 1205 (BK). TEST the system for normal operation.
  • Key in OFF position.
  • Measure the resistance between speed control servo C122 Pin 10, Circuit 1205 (BK), harness side and ground


  • Is the resistance less than 5 ohms?
A3 CHECK DEACTIVATOR SWITCH CIRCUITRY Yes

GO to A6 .

No

GO to A4 .
  • Measure the voltage between speed control servo C122 Pin 9, Circuit 636 (OG), harness side and speed control servo C122 Pin 10, Circuit 1205 (BK), harness side.


  • Is the voltage greater than 10 volts?
A4 CHECK CIRCUIT 10 (LG/RD) FOR AN OPEN Yes

GO to A5 .

No

REPAIR the circuit.

TEST the system for normal operation.
  • Disconnect: Deactivator Switch C2210.
  • Measure the voltage between deactivator switch C2210 Pin 1, Circuit 10 (LG/RD), harness side and ground.


  • Is the voltage greater than 10 volts?
A5 CHECK CIRCUIT 636 (OG) FOR AN OPEN Yes

INSTALL a new deactivator switch; REFER to Switch- Deactivator . TEST the system for normal operation.

No

REPAIR the circuit.

TEST the system for normal operation.
  • Measure the resistance between speed control servo C122 Pin 9, Circuit 636 (OG), harness side and deactivator switch C2210 Pin 2, Circuit 636 (OG), harness side.


  • Is the resistance less than 5 ohms?
A6 CHECK THE SPEED CONTROL ACTUATOR SWITCH ON CIRCUITRY Yes

GO to A9 .

No

GO to A7 .
  • Measure the voltage between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 10, Circuit 1205 (BK), harness side, while the speed control actuator switch ON is depressed.


  • Is the voltage greater than 10 volts?
A7 CHECK CIRCUIT 151 (LB/BK) FOR AN OPEN Yes

GO to A8 .

No

REPAIR the circuit.

TEST the system for normal operation.
  • Disconnect: Air Bag Sliding Contact C218a.
  • Measure the resistance between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and air bag sliding contact C218a Pin 4, Circuit 151 (LB/BK), harness side.


  • Is the resistance less than 5 ohms?
A8 CHECK THE AIR BAG SLIDING CONTACT Yes

INSTALL a new speed control actuator switch; REFER to Switch- Speed Control Actuator . TEST the system for normal operation.

No

INSTALL a new air bag sliding contact; REFER to Section.

TEST the system for normal operation.
  • Remove the air bag; REFER to Section.
  • Disconnect: Speed Control Actuator Switch.
  • Measure the resistance between bottom of air bag sliding contact Pin 1 (component side) and top of air bag sliding contact Pin 3 (component side).


  • Is the resistance less than 5 ohms?
A9 CHECK THE SPEED CONTROL ACTUATOR SWITCH ON CIRCUITRY FOR SHORT TO POWER Yes

GO to A10 .

No

GO to A12 .
  • Key in ON position.
  • Measure the voltage between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 10, Circuit 1205 (BK), harness side.


  • Is any voltage present?
A10 CHECK CIRCUIT 151 (LB/BK) FOR SHORT TO POWER Yes

REPAIR the circuit.

TEST the system for normal operation.

No

GO to A11 .
  • Key in OFF position.
  • Disconnect: Air Bag Sliding Contact C218a.
  • Key in ON position.
  • Measure the voltage between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 10, Circuit 1205 (BK), harness side.


  • Is any voltage present?
A11 CHECK THE AIR BAG SLIDING CONTACT Yes

INSTALL a new air bag sliding contact; REFER to Section.

TEST the system for normal operation.

No

INSTALL a new speed control actuator switch; REFER to Switch- Speed Control Actuator . TEST the system for normal operation.
  • Key in OFF position.
  • Remove the air bag; REFER to Section.
  • Disconnect: Speed Control Actuator Switch.
  • Key in ON position.
  • Measure the voltage between bottom of air bag sliding contact Pin 1 (component side) and ground.


  • Is any voltage present?
A12 CHECK THE SPEED CONTROL ACTUATOR SET/ACCEL CIRCUITRY Yes

GO to A13 .

No

INSTALL a new speed control actuator switch; REFER to Switch- Speed Control Actuator . TEST the system for normal operation.
  • Key in OFF position.
  • Measure the resistance between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 6, Circuit 848 (DG/OG), harness side, while the speed control actuator switch SET/ACCEL is depressed.


  • Is the resistance between 612 and 748 ohms?
A13 CHECK THE BPP SWITCH CIRCUITRY Yes

GO to A16 .

No

If automatic transmission, REPAIR Circuit 511 (LG) and Circuit 810 (LG/RD) as necessary. TEST the system for normal operation.

If manual transmission, GO to A14 .
  • Measure the resistance between speed control servo C122 Pin 4, Circuit 511 (LG), harness side, and speed control servo C122 Pin 10, Circuit 1205 (BK), harness side.


  • Is the resistance less than 20 ohms?
A14 CHECK CIRCUIT 511 (LG) AND CIRCUIT 810 (RD/LG) FOR AN OPEN Yes

GO to A15 .

No

REPAIR Circuit 511 (LG) and Circuit 810 (LG/RD) as necessary.

TEST the system for normal operation.
  • Disconnect: CPP Switch C2072.
  • Measure the resistance between CPP Switch C2072 Pin 1, Circuit 511 (LG), harness side and ground.


  • Is the resistance less than 20 ohms?
A15 CHECK CIRCUIT 511 (LG) FOR AN OPEN Yes

INSTALL a new CPP switch. TEST the system for normal operation.

No

REPAIR the circuit.

TEST the system for normal operation.
  • Measure the resistance between speed control servo C122 Pin 4, Circuit 511 (LG), harness side and CPP switch C2072 Pin 2, Circuit 511 (LG), harness side.


  • Is the resistance less than 5 ohms?
A16 CHECK CIRCUIT 239 (WH/OG) FOR AN OPEN Yes

GO to A17 .

No

REPAIR the circuit.

TEST the system for normal operation.
  • Disconnect: PCM C175.
  • Connect EEC-V 104-Pin Breakout Box.
  • Measure the resistance between speed control servo C122 pin 3, circuit 239 (WH/OG), harness side and Breakout Box, EEC-V Control System pin 68, circuit 239 (WH/OG), harness side.


  • Is the resistance less than 5 ohms?
A17 CHECK THE SPEED CONTROL SERVO Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

INSTALL a new PCM; REFER to Section. TEST the system for normal operation.
  • INSTALL a known good speed control servo.
  • Test drive the vehicle for correct operation.
  • Does the speed control operate correctly?

PINPOINT TEST B: THE SET SPEED FLUCTUATES

Test Step Result / Action to Take
B1 CHECK THAT CONDITION OCCURS ONLY WHILE USING SPEED CONTROL Yes

REPAIR engine as necessary. TEST the system for normal operation.

No

GO to B2 .
  • Check that the condition does not occur when driving without speed control.
  • Does the condition occur without speed control?
B2 CHECK THE SPEED CONTROL ACTUATOR CABLE Yes

GO to B3 .

No

INSTALL a new speed control actuator cable; REFER to Actuator Cable-Speed Control .

TEST the system for normal operation.
  • NOTE: The speed control actuator cable must be disconnected at both ends while carrying out this test.
  • Check the speed control actuator cable for sticking or binding at the speed control servo and throttle body.
  • Is the speed control actuator cable OK?
B3 CHECK THE SPEED CONTROL SERVO Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

INSTALL a new PCM; REFER to Section. TEST the system for normal operation.
  • INSTALL a known good speed control servo.
  • Test drive the vehicle for correct operation.
  • Does the speed control operate correctly?

PINPOINT TEST C: THE SPEED CONTROL DOES NOT DISENGAGE WHEN THE BRAKES ARE APPLIED

Test Step Result / Action to Take
C1 CHECK THE BPP SWITCH CIRCUITRY Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

REPAIR Circuit 810 (RD/LG) and Circuit 511 (LG) as necessary.

TEST the system for normal operation.
  • Key in OFF position.
  • Disconnect: Speed Control Servo C122 .
  • Measure the voltage between speed control servo C122 Pin 4, Circuit 511 (LG), harness side and speed control servo C122 Pin 10, Circuit 1205 (BK), harness side, while depressing the brake pedal.


  • Is the voltage greater than 10 volts?

PINPOINT TEST D: THE SPEED CONTROL DOES NOT DISENGAGE WHEN THE CLUTCH IS APPLIED

Test Step Result / Action to Take
D1 CHECK THE CLUTCH PEDAL POSITION (CPP) SWITCH Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

INSTALL a new CPP switch. TEST the system for normal operation.
  • Key in OFF position.
  • Disconnect: CPP Switch C2072.
  • Measure the resistance between CPP switch pin 2 (component side) and CPP switch pin 1 (component side),  while depressing and releasing clutch pedal.


  • Is the resistance greater than 10,000 ohms with the clutch pedal depressed and less than 5 ohms with the clutch pedal released?

PINPOINT TEST E: THE SPEED CONTROL SWITCH IS INOPERATIVE-COAST

Test Step Result / Action to Take
E1 CHECK THE SPEED CONTROL ACTUATOR SWITCH Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

INSTALL a new speed control actuator switch; REFER to Switch- Speed Control Actuator . TEST the system for normal operation.
  • Key in OFF position.
  • Disconnect: Speed Control Servo C122.
  • Measure the resistance between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 6, Circuit 848 (DG/OG), harness side, while pressing the speed control actuator switch COAST.


  • Is the resistance between 108 and 132 ohms?

PINPOINT TEST F: THE SPEED CONTROL SWITCH IS INOPERATIVE-SET/ACCEL

Test Step Result / Action to Take
F1 CHECK THE SPEED CONTROL ACTUATOR SWITCH Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

INSTALL a new speed control actuator switch; REFER to Switch- Speed Control Actuator . TEST the system for normal operation.
  • Key in OFF position.
  • Disconnect: Speed Control Servo C122.
  • Measure the resistance between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 6, Circuit 848 (DG/OG), harness side, while pressing the speed control actuator switch SET/ACCEL.


  • Is the resistance between 612 and 748 ohms?

PINPOINT TEST G: THE SPEED CONTROL SWITCH IS INOPERATIVE - RESUME

Test Step Result / Action to Take
G1 CHECK THE SPEED CONTROL ACTUATOR SWITCH Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

INSTALL a new speed control actuator switch; REFER to Switch- Speed Control Actuator . TEST the system for normal operation.
  • Key in OFF position.
  • Disconnect: Speed Control Servo C122.
  • Measure the resistance between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 6, Circuit 848 (DG/OG), harness side while pressing the speed control actuator switch RESUME.


  • Is the resistance between 1,980 and 2,420 ohms?

PINPOINT TEST H: THE SPEED CONTROL SWITCH IS INOPERATIVE-OFF

Test Step Result / Action to Take
H1 CHECK THE SPEED CONTROL ACTUATOR SWITCH Yes

INSTALL a new speed control servo; REFER to Actuator-Speed Control Servo . TEST the system for normal operation.

No

INSTALL a new speed control actuator switch; REFER to Switch- Speed Control Actuator . TEST the system for normal operation.
  • Key in OFF position.
  • Disconnect: Speed Control Servo C122.
  • Measure the resistance between speed control servo C122 Pin 5, Circuit 151 (LB/BK), harness side and speed control servo C122 Pin 6, Circuit 848 (DG/OG), harness side while pressing the speed control actuator switch OFF.


  • Is the resistance less than 5 ohms?

Switch Adjustment -Deactivator

1. Adjust the deactivator switch.

1. Disconnect the switch hook from the brake pedal.

2. Depress the switch hook and plunger into the deactivator switch body until the adjustment locking tab snaps into place within the hook.

3. Depress the brake pedal and reattach the switch hook.

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