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Cruise Control, How Do I Diagnose It Not Working?

September 16, 2018

 

My 2001 Ford F-150 cruise control stopped working out of the blue. It was working great one day and the next day, nothing. What do I need to check to solve this problem? - Paul

 

Paul, does your horn and brake light work? If the horn works, then this rules out the clock spring being defective. Here are the steps that you must follow to trouble shoot this problem IF the horn works.

  1. Disconnect the brake pressure switch on the master cylinder and inspect it for signs of brake fluid which may have leaked through the switch and is resulting in a contact problem.
  2. If the connector is wet with brake fluid, replace the brake pressure switch and check to see if the speed control recall has already been installed on this vehicle. This will be indicated by a fused jumper harness at the pressure switch connection.
  3. If the switch is clean, back probe the Light Blue/ Black (LB/BK) wire at pin 5 of the speed control servo to check it for voltage with the servo connected and the ignition switch in the Run position. Voltage should indicate 7.0-8.0 volts.
  4. If there is no voltage on this circuit when the servo is connected with the ignition switch in the Run position, check the Light Blue/Pink (LB/PK) wire at pin 7 to verify it is indicating battery voltage from fuse 5 (15 amp) of the Central Junction Box (CJB) and check for battery power on the Black/ Yellow (BK/YE) wire at pin 9 of the servo to verify it is good coming from the brake pressure switch and fuse 15 (5 amp) of the CJB.
  5. If the power feeds check to be OK, verify that the LB/BK wire is not shorted to ground. This can be done by checking for the horn to blow when pressing the speed control On switch. If the horn blows pushing the horn button but not the speed control on switch and the power supply feeds are good to the servo,the servo has a connection issue or is defective.
  6. If the LB/BK wire indicates correct voltage with the key in the Run position, check the voltage while holding down the ON switch. This should cause the circuit to indicate battery voltage. Releasing the switch should cause the LB/BK wire to return to the 7.0-8.0 volt value.
  7. Holding the SET/ACCEL button should cause the LB/BK wire to indicate approximately 4.5 volts. Releasing it should cause the LB/BK to return to the 7.0-8.0 volt value.
  8. If the speed control switch values check to be OK, verify that the Tan/Light Blue (TN/LB) wire at pin 4 of the servo indicates to be a ground from the Brake Pedal Position (BPP) switch located above the brake pedal. When stepping on the brake pedal, this ground should turn into a battery voltage input signal.
  9. The Vehicle Speed Sensor (VSS) input can be checked on the Grey/Black (GY/BK) wire at servo connector pin 3. This circuit should indicate a square wave signal with the transmission output shaft spinning fed from the Powertrain Control Module (PCM). The same circuit feeds the cluster for speedometer operation.
  10. If all signals check to be OK, check to verify that the control cable running to the throttle body is not binding before replacing the servo.

If you think this work is complicated, give us a call at James Auto Center 850-763-0555 and for about 1 hour diagnostic time, we can solve your problem...

 

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For James Auto Center


 

1301 E. 11th Street

Panama City, FL 32401

 

(850) 763.0555 phone

 

 

Hours of Operation

M-F from 7am to 5pm

 

 

 

 

 

 

James Auto Center

Panama city auto service & repair

 

(850) 763.0555

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