P0859 OBD-II Trouble Code: Traction Control Input Signal High

P0859 code definition

A P0859 trouble code indicates that the vehicle's Powertrain Control Module (PCM) has reported a malfunction relating to the traction control input signal circuit.

What the P0859 code means

The traction control system regulates several aspects of the vehicle's drive system, particularly with regards to engine power and fuel delivery. A P0859 trouble code will be logged on the vehicle's computer if the PCM fails to receive a signal from the traction control system.

What causes the P0859 code?

• In the vast majority of cases, the P0859 code is caused by a defective traction control switch. The switch itself may be faulty or damaged. Technicians report defective switches in this code instance are often damaged due to liquid contact.

• Shorted, corroded and damaged wires may also be to blame for a P0859 signal malfunction. Moreover, technicians have cited a corroded sensor connector as a common reason for this trouble code.

What are the symptoms of the P0859 code?

The reported symptoms of a P0859 code vary from purely traction-related concerns to a failure of the transmission system. Traction problems are most commonly reported, particularly if a P0859 code-afflicted car is driven on slippery surfaces. Harsh or failed shifting may also come alongside a P0859 code. The P0859 trouble code and dashboard trouble indicator will both be activated for the sake of highlighting and diagnosing the concern.

How does a mechanic diagnose the P0859 code?

A technician may first diagnose the P0859 code by reading it via an OBD-II code reader. Components related to the traction system (particularly the traction control system's activation switch) should be inspected and tested for signs of fault or malfunction. All wires relating to the traction control system should be inspected thoroughly in order to verify any potential signs of corrosion, damage, wear or disconnection. In the case that there is a possible issue with one of the vehicle's control modules, a specialized scanner (such as an Autohex) may be used in order to pinpoint the source of the problem.

Common mistakes when diagnosing the P0859 code

Although a faulty traction control module is sometimes to blame for a P0859 code, it is often mistakenly replaced when the real problem lies with broken electrical circuitry or a faulty switch.

How serious is the P0859 code?

A P0859 trouble code can result in drivability issues for the vehicle. Particularly if the vehicle's typical driving surfaces are slippery, a P0859 code can make the vehicle more dangerous to drive. In addition, an unpredictable transmission system resulting from a P0859 can make driving the vehicle a precarious situation.

What repairs can fix the P0859 code?

• If the traction control system's activation switch have been identified as faulty, it should be a relatively simple process of removing and replacing the component. Any other components that have been identified as faulty should be repaired or replaced accordingly.

• Any wiring you've identified as being sufficiently corroded, damaged or disconnected should be repaired or replaced as needed.

• After conducting your repairs, retest the vehicle to see whether or not the trouble code returns.

Additional comments for consideration regarding the P0859 code

The P0859 trouble code only applies to vehicles with electronic traction control systems. Due to the high amount of circuitry associated with this code and the traction system, it is recommended that these repairs be left to a proper technical specialist.

Need help with a P0859 code?

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