What it means
U0126 is a generic network DTC (second digit 0) indicating that one or more controllers stopped receiving required messages from the Steering Angle Sensor (SAS) module. On most light-duty platforms, SAS data is published on the high-speed CAN (HS-CAN ~500 kbps) segment used by chassis/driver-assist systems (ABS/ESC/EBCM, EPAS/PSCM), the gateway, and sometimes directly by the ECM/PCM. Some OEM topologies house the SAS within or adjacent to a column/steering module and still broadcast angle over HS-CAN; a few platforms may route SAS through a body/mid-speed network via a gateway—check platform wiring. The SAS value is critical for ESC/ABS, EPAS assist logic, and ADAS alignment, so a loss of SAS messages can disable stability/assist features. OBD-Codes.com+2Charm+2
Typical symptoms
- ABS/ESC/“Stability” and steering-assist warnings; possible “Steering Assist Reduced/Service” message
- EPAS may default to reduced assist; driver-assist/ADAS features may be unavailable
- Scan tool shows U0126 in multiple modules (e.g., ABS/EBCM, PSCM, IPC); SAS module appears offline intermittently or continuously
- After battery events or body/column work: persistent U0126 with no other codes until communication is restored/recalibrated OBD-Codes.com
Why it sets (representative OEM logic)
- Message timeout from SAS: Supervising modules (ABS/EBCM, PSCM, gateway/IPC, ECM) do not receive SAS messages within calibrated timers, so they set U0126. This is a “lost communication” monitor, not a specific sensor-value plausibility fault. OBD-Codes.com
- CAN physical-layer faults: Opens/shorts/termination faults or a node holding the bus dominant cause missed messages. OEM HS-LAN guidance specifies ~60 Ω ±5 Ω across HS-CAN (key off) at DLC pins 6–14; <60 Ω suggests a short/extra terminator; >60 Ω suggests an open/missing terminator. NHTSA
- Key-on electrical expectations (HS-CAN): At rest, typical bias is ~2.6 V on CAN_H and ~2.4 V on CAN_L with small fluctuation; significant deviation or a stuck line indicates a physical-layer fault. OBD-Codes.com
- OEM nuance: GM service information explicitly treats U0126 as “Lost Communication with B99 Steering Wheel Angle Sensor Module” and directs technicians to standard U-code wiring/CAN diagnostics (not immediate parts replacement). NHTSA
Common root causes
- Power/ground loss at the SAS/steering column module (blown fuse, poor ground, low system voltage)
- HS-CAN wiring faults (opens/shorts to B+/ground, CAN_H↔CAN_L short), damaged splices or junctions near the column/dash
- Termination problems on the HS-CAN backbone (missing/failed 120-Ω end → bus total ≠ ~60 Ω)
- Connector/pin issues at the SAS/SCCM/clock-spring interface (backed-out pins, corrosion, water intrusion)
- Internal SAS/transceiver failure intermittently going error-passive/bus-off
- Aftermarket device interference (DLC dongles, remote starts, trackers) disturbing network or module power feeds OBD-Codes.com+1
Professional diagnostics (step-by-step)
Network overview & scan strategy
- Perform a global DTC scan. Note all U-codes and which modules report SAS missing; identify modules that are offline. Use the scan tool’s topology/gateway map to confirm where the SAS lives (standalone SASM, within SCCM/PSCM, etc.) and which network segment carries SAS data. Charm
Power/ground checks at the SAS module
- At the SAS/SCCM connector, verify B+, IGN feed, and ground under load (target ground drop ≤100–200 mV). A powered-down SAS will appear as network loss to other controllers. Clear/verify after correcting any feed/ground issues. OBD-Codes.com
Bus integrity tests (HS-CAN)
- Key-off resistance: Measure between DLC pins 6 & 14. Expect ~60 Ω ±5 Ω.
– >60 Ω ⇒ open/missing terminator/branch; <60 Ω ⇒ short/extra terminator. NHTSA - Key-on voltage checks: At rest, confirm ~2.6 V CAN_H / ~2.4 V CAN_L at an accessible node. Lines stuck near 0 V or 5 V (or no differential swing) indicate a hard fault. OBD-Codes.com
- Oscilloscope (preferred): Verify clean differential waveform; look for reflections/noise suggesting termination or grounding issues. (Follow OEM HS-LAN method.) NHTSA
Segment/branch isolation
- If the whole HS-CAN is impacted, isolate network halves/branches per OEM guidance (pull module fuses, disconnect junctions) while monitoring when comms return. GM’s HS-LAN procedure details splitting the bus and acceptable resistance changes during isolation. NHTSA
Connector & harness inspection (column/airbag clockspring area first)
- Perform pin-drag tests at the SAS/SCCM and nearby junctions; inspect for backed-out pins, water/corrosion, chafed pairs, or prior repair splices near the steering column, lower dash, and kick panels. Repair and re-secure the twisted pair. Charm
Aftermarket device audit
- Remove or disable DLC-attached devices (insurance dongles, trackers) and any splices into HS-CAN/power. Re-evaluate network stability after removal. NHTSA
Module-level steps (only after bus health is proven)
- If wiring/termination/power are good and SAS remains offline, check for calibration/software updates; many SAS/column modules require initialization/calibration after repair. Replace/initialize the SAS or related module per OEM programming only after confirming the network is healthy. OBD-Codes.com
Verified fixes
- Restore SAS power/grounds; repair blown fuses/poor grounds/low voltage
- Repair HS-CAN wiring (opens/shorts) and damaged splices; maintain proper twist/routing
- Restore correct termination (two 120-Ω ends ≈ 60 Ω total); correct star/junction faults
- Clean/repin SAS/SCCM/column connectors; correct pin tension and water intrusion
- Remove/rewire interfering aftermarket DLC devices
- Calibrate/initialize the SAS after repairs; update software or replace/program the SAS/column module if confirmed faulty
- Clear codes, perform a drive cycle, and re-scan to confirm. NHTSA+1
Sources
- OBD-Codes – U0126: Lost Communication with Steering Angle Sensor (SAS) Module — technical description, power/ground emphasis, and HS-CAN voltage checks (~2.6 V / ~2.4 V). OBD-Codes.com
- GM/ACDelco via NHTSA — “Diagnostic Tips: Diagnosing High-Speed LAN Concerns” — OEM procedure with ~60 Ω ±5 Ω spec at DLC pins 6 & 14 and bus-isolation strategy. NHTSA
- GM Preliminary Information (NHTSA) — U0126 framed as “Lost Communication with B99 Steering Wheel Angle Sensor Module” and directs use of standard U-code wiring/CAN diagnostics. NHTSA
- Toyota OEM Service Content (mirror) — U0126 definition and CAN relationships among Skid Control ECU, steering angle sensor, ECM (example: Highlander/Tundra). Charm+1
- RepairPal — U0126: Lost Communication with Steering Angle Sensor Module — plain-language overview, symptoms, and diagnostic framing (secondary corroboration). RepairPal.com