Error Code P0856 is defined as Traction Control Input Signal. Error Code P0856 is a generic trouble code, meaning it applies to all vehicles with the OBD-II system, especially those made from 1996 up to the present. It also applies to vehicles with both automatic transmission and 4WD capability. Specifications on the definition, troubleshooting, and repairs vary between make, model, and powertrain configuration.
The PCM (powertrain control module) and a set of modules receive data from the traction control input signal. The PCM (and other modules) uses this data to determine the proper RPM, engine timing, fuel delivery of the engine, and various other functions. When the traction control module fails, this will send a signal to the PCM and store the error code.
As with other error codes, the Check Engine Light is activated with this code. Other common symptoms include:
- Malfunctioned or inoperable traction control system (loss of grip, slippery on icy conditions)
- Increase in fuel consumption
- Difficulty shifting or may not shift at all
The most common cause of this code is a faulty On/Off traction control system switch. This could be a result of spills or leaks that damages the control switch. Other possible causes include:
- Faulty, loose, or damaged connectors, wires, and other electrical components
- Corrosion in the traction control sensor connector
- Defective traction control module (rare)
How to Check
Start the diagnosis using a standard OBD-II trouble code scanner to get the freeze frame data and other related codes. Reset the codes and restart the vehicle. If the code doesn’t come back, it means you have an intermittent problem. This means the code may have been triggered erroneously, or it’s an intermittent problem.
If the code comes back, however, then check the electrical components of the traction control system. See if there are any damaged, loose, or corroded connectors and wires. Replace any damaged components as necessary. If there On/Off switch is faulty or damaged, replace it as well.
Reset the code and restart the vehicle every time you replace a component. This will help you tell whether the issue has been resolved or not.
How to Fix
- Repair or replacement of faulty or damaged connectors and wires in the traction control module
- Repair or replacement of faulty On/Off switch in traction control module
- Replacement of damaged traction control module (rare)
When addressing this code, the most common mistake is replacing the traction control module when the problem is just a faulty On/Off switch or defective electrical components.
A vehicle with this code is still drivable. However, since it disables the traction control system, that means the vehicle is unsafe to use in icy or wet roads.