Definition of Code P0856
The fault code P0856 detects a problem with the traction control input signal.
What does code P0856 mean?
Code P0856 is a standard OBD-II trouble code that indicates an issue with the traction control input signal. The traction control input signal is responsible for sending data to the Powertrain Control Module (PCM) and other control modules. The PCM and other control modules use this data to determine the appropriate revolutions per minute (RPM) for the vehicle, as well as engine timing, fuel distribution, and many other factors. When the PCM and associated control modules do not receive input signals from the traction control module, the fault code P0856 will be triggered.
What causes code P0856?
Fault code P0856 is typically caused by a faulty ON/OFF switch in the traction control system. This is usually the result of spills or leaks damaging the control switch, or faulty, loose, or damaged wires, connectors, and other electrical components in the system. In addition to a faulty switch, corrosion on the traction control sensor connector can lead to the detection of code P0856. Although rare, the traction control module itself may also be faulty.
What are the symptoms of code P0856?
When fault code P0856 is detected, the Check Engine warning light will soon illuminate on the instrument panel, and the traction control fault light will likely also turn on. In addition to these warnings, the traction control system is likely to stop functioning, which may result in a loss of grip (primarily on slippery or icy surfaces). The transmission may also have difficulty shifting gears or may not shift at all (and may enter limp mode), and the vehicle will likely experience reduced fuel economy.
How does a mechanic diagnose code P0856?
Code P0856 should be diagnosed using a standard OBD-II fault code scanner. A qualified mechanic will use the scanner to view freeze frame data and assess the code. The mechanic will also check for the presence of additional fault codes. The codes should then be reset, and the vehicle restarted to see if the code persists. If the code does not return, it was likely triggered by mistake or represents an intermittent issue.
If fault code P0856 returns, the mechanic must visually inspect the electrical components of the traction control system to check for loose, damaged, or corroded wires and connectors. Any damaged components should be replaced. If the technician notices that the ON/OFF switch is also damaged, it must be replaced.
Whenever a component is replaced, the codes should be reset and the vehicle restarted before the mechanic proceeds. This will allow the mechanic to determine whether the issue has been resolved or if further work is needed.
Common mistakes when diagnosing code P0856
The most common mistake made when diagnosing code P0856 is not following the OBD-II fault code diagnostic protocol. All mechanics must follow the protocol correctly to ensure that the diagnosis and repair are not only performed accurately but also effectively.
It is common for the traction control module to be replaced when the only issue was a faulty ON/OFF switch or damaged electrical components.
How severe is code P0856?
A vehicle with fault code P0856 present is still drivable. However, the vehicle’s traction control system will likely be disabled, meaning the car will not have good traction on wet or icy roads. Additionally, unnecessary strain may be placed on the transmission, which could eventually cause damage. Even though the car can be driven, code P0856 should be inspected and resolved as soon as possible.
What repairs can fix code P0856?
- Some possible repairs for fault code P0856 include:
- Replacement of the traction control module wires and connectors
- Replacement of the ON/OFF switch in the traction control module
- Replacement of the traction control module itself