Definition of Code P0859
A fault code P0859 indicates that the vehicle’s Powertrain Control Module (PCM) has reported a malfunction related to the traction control input signal circuit.
What does code P0859 mean?
The traction control system regulates several aspects of the vehicle’s drive system, particularly concerning engine power and fuel distribution. A fault code P0859 will be logged in the vehicle’s computer if the PCM does not receive a signal from the traction control system.
What causes code P0859?
In the vast majority of cases, code P0859 is due to a faulty traction control switch. The switch itself may be defective or damaged. Technicians report that faulty switches in this code instance are often damaged due to liquid contact.
Shorted, corroded, and damaged wires can also cause a P0859 signal malfunction. Additionally, technicians have cited a corroded sensor connector as a common reason for this fault code.
What are the symptoms of code P0859?
Reported symptoms of a P0859 code range from purely traction-related issues to transmission system failure. Traction problems are most commonly reported, especially if a car afflicted by code P0859 is driving on slippery surfaces. A harsh or failed shift may also be associated with a P0859 code. Both the P0859 fault code and the dashboard warning light will be activated to highlight and diagnose the problem.
How does a mechanic diagnose code P0859?
A technician can first diagnose code P0859 by reading it via an OBD-II code reader. Components related to the traction system (especially the traction control system activation switch) should be inspected and tested for any signs of fault or malfunction. All wires related to the traction control system must be thoroughly inspected to check for any potential signs of corrosion, damage, wear, or disconnection. If there is a possible issue with one of the vehicle’s control modules, a specialized scanner (such as an Autohex) can be used to identify the source of the problem.
Common mistakes when diagnosing code P0859
Although a faulty traction control module is sometimes to blame for a P0859 code, it is often mistakenly replaced when the real problem lies in broken electrical circuits or a faulty switch.
How severe is code P0859?
A P0859 fault code can lead to driving problems for the vehicle. Especially if the vehicle’s typical driving surfaces are slippery, a P0859 code can make the vehicle more dangerous to drive. Additionally, an unpredictable transmission system resulting from a P0859 can make driving the vehicle a precarious situation.
What repairs can fix code P0859?
If the traction control system activation switch has been identified as faulty, it should be a relatively simple process to remove and replace the component. Any other component identified as faulty should be repaired or replaced accordingly.
Any wiring that you have identified as sufficiently corroded, damaged, or disconnected should be repaired or replaced as needed.
After performing your repairs, retest the vehicle to see if the fault code returns or not.