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

Check Engine Light

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?

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?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701- 6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

More related articles

How to Get a Louisiana Driver's Permit
s licensing program. The first step in this program is to obtain...
Veteran and Military Driver Laws and Benefits in New Mexico
The state of New Mexico offers a number of benefits and perks for those Americans who have either served in an Armed Forces branch...
Auto Safety Tips
Driving is more than a way to get from point A to point B. Owning and driving a car can also be a highly enjoyable experience. Whether a person is driving...

Related questions

Q: While highway driving, car stopped accelerating & became inoperative

This message indicates there is a problem in the anti-lock braking and/or electronic stability program system. If the problem is severe enough, the vehicle will go into limp mode, as you experienced. The root cause could be anything from a...

Q: Dashboard is working partially

Hey there. It sounds like it is having serious wiring issues. It is quite possible that one or more wires shorted. This is a potentially dangerous situation, and should be inspected immediately before getting back on the road. If you...

Q: the car wont pass emmissions the code po420 comes up

Fault code P0420 indicates the catalytic converter is operating below proper efficiency. There are two oxygen (O2) sensors in the exhaust system. One just before and one just after the catalytic converter. The ecu reads the first O2 sensor to...