P0856
Traction Control Input Signal
- Severity
- Medium
- Driving
- Drivable — book it in
A fault in the traction control input signal to the transmission module. When the traction control system detects wheelspin it asks for reduced torque and, on many vehicles, for the transmission to hold or change gear. Without that signal the two systems cannot coordinate, so traction control may be disabled or less effective.
Possible causes
- CommonWiring or bus fault between the traction control and transmission modules
- CommonFault in the ABS or traction control module itself
- PossibleCorroded connector at either module
- PossibleWheel speed sensor fault upstream, so the signal is missing at source
- PossibleLow battery voltage dropping a module off the bus
What you might notice
- Traction control warning light on
- Traction control inoperative
- Transmission not responding to wheelspin
- ABS warning light on as well
- Check engine light on
What to check, in order
- Read the ABS and traction control modules as well. The fault is usually there, and this code is only the transmission module noticing.
- Check battery voltage and state of charge - a weak battery drops modules off the bus and produces communication faults with no wiring problem at all.
- Look for wheel speed sensor codes, which would explain a missing signal at source.
- Inspect the connectors at both modules.
- Assume traction control is not working and drive accordingly, particularly in the wet or on loose surfaces.
Read this code from your own car
Plug an ELM327 adapter into the OBD-II port under the dashboard. Pin16 reads every stored, pending and permanent code, explains each one like this page does — offline, with no account — and shows what the car recorded when the fault was set.
Where this code sits
P00xxP01xxP02xxP03xxP04xxP05xxP06xxP07xxP08xxP09xxP0AxxP0BxxP0CxxP0DxxP0ExxP0FxxP10xxP11xxP12xxP13xxP14xxP15xxP16xxP17xxP18xxP19xxP1AxxP1BxxP1CxxP1DxxP1ExxP1FxxP20xxP21xxP22xxP23xxP24xxP25xxP26xxP27xxP28xxP29xxP2AxxP2BxxP2CxxP2DxxP2ExxP2FxxP30xxP31xxP32xxP33xxP34xxP35xxP36xxP37xxP38xxP39xxP3AxxP3BxxP3CxxP3DxxP3ExxP3Fxx
Transmission
P0800P0801P0802P0803P0804P0805P0806P0807P0808P0809P0810P0811P0812P0813P0814P0815P0816P0817P0818P0819P0820P0821P0822P0823P0824P0825P0826P0827P0828P0829P0830P0831P0832P0833P0834P0835P0836P0837P0838P0839P0840P0841P0842P0843P0844P0845P0846P0847P0848P0849P0850P0851P0852P0853P0854P0855P0856P0857P0858P0859P0860P0861P0862P0863P0864P0865P0866P0867P0868P0869P0870P0871P0872P0873P0874P0875P0876P0877P0878P0879P0880P0881P0882P0883P0884P0885P0886P0887P0888P0889P0890P0891P0892P0893P0894P0895P0896P0897P0898P0899