Fault code P0859 – traction control input signal high

Fault code P0859 is called “Traction Control Input Signal High” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0859

OBD-II fault code P0859 is defined as a high level of traction control input signal. It is set when a communication fault is detected between the PCM and the traction control module.

Fault code P0859 – traction control input signal high

Traction Control is designed to prevent wheels from slipping on wet or slippery surfaces. It works in conjunction with the ABS system to selectively apply braking forces to the spinning drive wheels.

In practice, traction control systems take advantage of a design feature of differentials that allows the drive wheels to spin independently of each other. Thus, when the vehicle turns, the inner drive wheel slows down. While the speed of the outer drive wheel increases because it has to travel a greater distance.

While the traction control system is operating, the control module can limit or even ignore the driver’s throttle pedal pressure. To prevent shifting gears that could exacerbate wheel slip conditions.

In practice, the traction control system uses the same wheel speed sensors as the ABS system, as well as all other components.

Thus, the system depends on effective communication between all the sensors involved. Such as wheel speed sensors, engine speed sensors, throttle position and various transmission sensors.

If communication between the sensors and control modules is interrupted for any reason, especially between the PCM and the traction control control module. The PCM realizes that it cannot effectively control the traction control system, and as a result, code P0859 is set, followed by a warning light.

On some vehicles, setting this code may not only disable the traction control system. Stability system, cruise control and ABS braking function may also stop working.

Which systems are disabled and whether or not the vehicle goes into restricted mode depends on the specific vehicle.

Symptoms of vehicle malfunctions

The main signal that an error P0859 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. Check engine control lamp on the control panel will light up (the code will be recorded in the memory as a fault).
  2. The traction control system is disabled.
  3. Stability control system does not work.
  4. Cruise control cannot be activated.
  5. ABS brake function is disabled.

Fault P0859 is considered not very serious, the car will be able to continue driving. But still it is better to solve the problem as soon as possible, because with this fault a failure of auxiliary systems is possible.

Factors that can cause this error code

The error code P0859 can mean that one or more of the following problems have occurred:

  • Defective traction control switch.
  • Defective wheel speed sensor or associated gear ring.
  • Damaged, burned, shorted, disconnected, or corroded wiring or connectors.
  • Defects, malfunctions, or failures in the ABS system.
  • Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P0859

Some suggested steps for troubleshooting and fix the error code P0859:

  1. Read all stored data and error codes with an OBD-II scan tool.
  2. Clear the error codes from the computer memory.
  3. Test-drive the vehicle to find out if fault P0859 appears again.
  4. Check the traction control switch.
  5. Visually inspect the wires and connectors in the traction control and ABS systems.
  6. Check the wheel speed sensor or associated gear ring.
  7. Test the engine control module (PCM).

Diagnose and repair of problems

Diagnosing the P0859 problem should begin by checking the service bulletins (TSB) for your specific vehicle. Your problem may be known, which can save you time and money during diagnosis.

The most common cause of this error is a faulty traction control switch. It should be tested with a multimeter.

Further diagnostic steps include a visual inspection of all relevant wires and connectors associated with the system. Also check the wheel speed sensor and the associated toothed ring for damage and functionality.

In case the P0859 error remains after the performed tests, it is necessary to test the engine control module. But these actions should be entrusted to professionals, as you probably won’t be able to do it at home.

On which vehicles does this problem occur most frequently

Fault code P0859 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Ford

Fault code P0859 can sometimes be found with other errors. The most common are the following: P0856, P0857, P0858.


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