U0126 — Lost Communication With Steering Angle Sensor Module | Steering Angle Signal Fault

Causes

• Open or shorted CAN bus wiring between SAS module and other controllers
• Faulty steering angle sensor module (internal failure)
• Poor power or ground at the SAS module
• Corroded or loose connector(s) at the SAS, clock spring, or steering column
• Failed termination resistor(s) or incorrect bus impedance
• Low battery/voltage issues or intermittent supply

Symptoms

• ABS, ESC/ESP or VSM warning lamps illuminated
• Loss or reduction of stability control/traction control functions
• Steering-angle dependent features (lane-keep, adaptive cruise) disabled
• Steering wheel angle reading missing or erratic in scan tool live data
• Possible EPS (electric power steering) warning or reduced assist
• Intermittent or persistent communication errors stored in multiple modules

What to check

• Read DTCs in all modules and note any related U-codes (other lost-comm codes)
• Verify battery voltage is within spec and charging system is OK
• Visually inspect connectors, pins and wiring at the SAS, clock spring and steering column for damage, corrosion or loose pins
• Check fuses and power/ground circuits feeding the SAS module
• Use a scan tool to see whether the SAS module is present on the CAN network and whether it broadcasts angle data
• Backprobe CAN_H and CAN_L at the SAS connector; verify idle voltages and activity with a scope or lab scope function

Signal parameters

• CAN bus idle voltages: CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each to chassis ground) with small offset
• Dominant bus state (logic 0): CAN_H ≈ ~3.5 V, CAN_L ≈ ~1.5 V (differential ~2.0 V)
• Recessive bus state (logic 1): both lines ≈ 2.5 V, differential ≈ 0 V
• Termination resistance: ~60 Ω measured across CAN_H and CAN_L (modules removed or ignition off depending on vehicle)
• SAS message frequency: typically periodic updates (tens of Hz) — missing periodic frames indicates lost communication

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