U01EF87 - U01EF87 SWS Signal Invalid (SWS Signal Value Invalid Fault)

U01EF87 SWS Signal Invalid Fault Technical Analysis

Fault Depth Definition

U01EF87 fault code (SWS Signal Invalid) identifies data integrity check failure in the vehicle network communication system. In smart driving assist system architecture, SWS (Steering Wheel Switch) as a critical status input source is responsible for feedback steering wheel operating state and physical position information to the central control unit. The specific meaning of this fault refers to that the SWS signal value received by the controller exceeds the preset valid logic range or cannot match the current system state.

This fault belongs to network communication class diagnostic code (U series), indicating that although the bus connection is established, the data content provided by the upstream node exists untrustworthiness. For electronic control units relying on steering wheel input for safety logic determination, failure of SWS signal means "driver intent feedback loop" interruption, may cause control system unable to confirm current human-machine interaction state, thereby triggering protection mechanism to isolate risk.

Common Fault Symptoms

When vehicle detects invalid SWS signal value and records U01EF87, partial core functions of Advanced Driver Assistance System (ADAS) will enter fail-safe mode. Based on diagnostic data logic inference, main symptoms owners can perceive during driving include:

• Partial ADAS functions unavailable, such as lane keeping or automatic following etc functions relying on steering wheel state judgment are disabled.
• Dashboard displays related safety warning messages, indicating abnormality in steering wheel input signal.
• Vehicle Electronic Stability Program or other integrated modules may restrict specific power output strategies due to lack of valid directional input.

Core Fault Cause Analysis

According to existing diagnostic data "Steering Wheel Switch Failure", combined with automotive electronic system architecture principles, causes leading to this fault can be summarized into following three technical dimensions for logic analysis:

1. Hardware Component Level (Steering Wheel Switch): Fault root cause may lie in steering wheel switch sensor or internal circuit module. If contacts inside switch oxidize, micro switches damaged or signal output chip failed, will directly produce unexpected voltage level or digital jump, causing controller judge as "Invalid" signal value. This is direct feedback of hardware physical characteristics.

2. Wiring and Connector Level (Physical Connection): Although raw data did not clearly point to harness, but in technical logic, physical link integrity from steering wheel switch output end to controller input end is crucial. Connector loose, pin corrosion or signal transmission path interfered by electromagnetic interference, may cause collected voltage drift or signal timing abnormality, subsequently trigger controller thinking received SWS value invalid.

3. Controller Level (Logic Operation and Threshold Determination): Vehicle electronic control unit internal software logic responsible for checking if input SWS values are within allowed voltage window. If controller sampling algorithm deviate, calibration data mismatch or internal processing module instant anomaly, may cause valid signal incorrectly marked as invalid fault.

Technical Monitoring & Trigger Logic

Generation of this fault code is not instantaneous trigger, but went through a series of rigorous monitoring conditions and system state verification. Detailed parameters of diagnostic logic are as follows:

• Monitoring Target System continuously monitors steering wheel switch output analog voltage or digital signal level, ensure it is within pre-defined reasonable working interval, while verifying CAN bus communication status and data synergy with Body Control Module (BCM).

• Value Range Determination Fault determination relies on strict electrical parameter thresholds. Controller only monitors when power stable and satisfies specific voltage range conditions: $$ 9V \sim 16V $$ Within this voltage range, if collected SWS signal value does not meet logic requirements or exceeds calibration limit, regarded as invalid.

• Trigger Sequence Conditions Formal record of fault code needs to satisfy following specific time sequence and system state combinations:

  • Power On Initialization Wait: After vehicle power on, need pass $3s$ initialization time, to ensure power stable and bus ready.
  • Network Status Constraints: Public CAN bus must not enter busoff (bus off) status, ensure communication link still effective.
  • Mode and Synergy Check: System in non-factory mode (Factory mode disabled), and received no power-down notification from Body Control Module (BCM).
  • Fault Confirmation Delay: After first detected service detection DTC, continue monitor $3s$ if still satisfy above conditions, then finally confirm valid fault and store fault code.