Code
P056B
Generic
P — Powertrain
Cruise Control Decrease Distance Signal
Views:
UK: 18
EN: 25
RU: 17
AI status
Completed
Completed
100%
Causes
- Faulty or stuck steering wheel cruise/distance decrease switch
- Open, shorted, or corroded wiring/connectors between switch and body control module (BCM) or steering wheel module
- Defective clockspring (spiral cable) in steering column
- Loss of CAN/LIN communication between driver controls, BCM and ACC (Adaptive Cruise Control) module
- Faulty ACC/radar module or BCM internal fault
- Software mismatch or incomplete module programming
Symptoms
- Pressing the distance-decrease button has no effect
- Adaptive cruise does not reduce following distance when commanded
- Cruise/ACC warning or malfunction lamp on instrument cluster
- Stored P056B in the powertrain or body control module memory
- Intermittent ACC behavior or loss of some cruise functions
What to check
- Scan all modules; record freeze-frame and related codes (look for CAN/U codes)
- Verify battery and charging system voltage and stability
- Operate distance increase/decrease switches while watching live data from ACC/BCM/steering module
- Visually inspect wiring and connectors at steering wheel, clockspring, BCM, and ACC module
- Check CAN/LIN bus integrity and message flow with a capable scan tool or scope
- Inspect for recent module replacements or software updates that may need reprogramming
Signal parameters
- Command source: steering wheel switch or stalk (may pass through steering module/BCM)
- Signal type: digital command transmitted over vehicle network (CAN or LIN) or discrete switch input to BCM
- Expected behavior: switch generates a momentary command when pressed; network message with decrease-distance flag appears at ACC module
- Nominal network: CAN at vehicle-specific baud rate (commonly 250 kb/s or 500 kb/s) — check OEM specs
- If discrete: switch = near 0 V or battery voltage when activated depending on wiring (verify with schematic)
Diagnostic algorithm
- Read and record all stored DTCs and freeze-frame data from all modules. Note related communication (U0xxx) codes.
- Clear codes and attempt to reproduce P056B by pressing the distance decrease control while monitoring live data from BCM/steering module and ACC module.
- If the command is not seen at module data, test the steering wheel switch for proper operation and continuity. Check for stuck contacts.
- Inspect and test the clockspring for continuity on switch circuits if steering wheel switch signals are not reaching the module.
- Check connectors and wiring between steering wheel/steering module, BCM and ACC module for damage, corrosion, or poor pins. Repair as needed.
- Verify CAN/LIN bus health: check termination resistances, voltage levels with the ignition on, and message traffic with a scanner or oscilloscope.
- If network messages from the switch reach the BCM but not the ACC module, suspect BCM or ACC module fault — consult manufacturer data and consider module bench testing or replacement.
- If modules were recently replaced or updated, verify correct software calibration and perform any required reprogramming or module coding.
- After repair, clear codes and perform road test to confirm the decrease-distance command functions and code does not return.
Likely causes
- Steering wheel decrease-distance switch or stalk failure
- Damaged clock spring wiring for steering wheel switches
- Connector corrosion or pin damage at BCM/steering module/ACC module
- CAN bus wiring fault, high resistance or short to battery/ground
- Faulty ACC control unit or BCM requiring replacement or reflash
Fault status
Status
Stored/Current DTC P056B — Cruise Control Decrease Distance Signal. Possible switch, wiring, clock spring, CAN or ACC module fault. Adaptive cruise may not reduce following distance.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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