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DTC codes / U04xx · Invalid data received from a module / U0420

U0420Invalid Data Received From Power Steering Control Module

U0420 is a communication fault indicating that the power steering control module (PSCM) is sending data that other modules consider invalid or corrupted. The vehicle's network gateway or another controller has received messages from the PSCM, but the data content fails plausibility or checksum validation, so the system cannot trust the steering assist information.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaInvalid data received from a module

Symptoms you may notice

  • Power steering warning light illuminated on the dashboard
  • Heavy or stiff steering effort, especially at low speeds
  • Intermittent loss of power steering assist while driving
  • Steering assist may default to a fixed mode or shut off completely
  • Often no symptoms besides the warning light if the fault is intermittent
  • Other dashboard warnings (stability control, ABS) may appear if shared data is affected

Common causes, most likely first

  1. Faulty power steering control module (PSCM) internal error or corrupted software
  2. Damaged or chafed wiring in the controller area network (CAN) bus or dedicated data lines to the PSCM
  3. Poor electrical connection at the PSCM connector, often due to corrosion or loose pins
  4. Low or unstable battery voltage causing the PSCM to send invalid data frames
  5. Failed or failing power steering motor or torque sensor feeding bad data to the PSCM
  6. Network gateway or another module misinterpreting valid PSCM data due to its own fault
  7. Aftermarket accessories or improper jump-starting that disrupted module communication

How to diagnose and fix it

  1. Verify battery voltage and charging system health; low voltage is a common root cause of invalid data
  2. Inspect the PSCM connector and wiring for corrosion, loose pins, or chafing near moving components
  3. Perform a wiggle test on the PSCM harness while monitoring live data to catch intermittent faults
  4. Check for technical service bulletins (TSBs) or software updates for the PSCM and related modules
  5. Use a scan tool to clear the code and road-test; if it returns, proceed to module-level diagnostics
  6. Measure CAN bus resistance and check for shorts or opens on the data lines between the PSCM and gateway
  7. If wiring and power are confirmed good, replace and reprogram the PSCM as the final step

What Most Techs Miss on U0420

  • A weak battery or failing alternator often sets U0420 before any steering symptom appears, so always load-test the battery first.
  • The PSCM can send valid but implausible data due to a failing internal torque sensor, which does not always set a separate sensor code.
  • Aftermarket electrical accessories tapped into the CAN bus can corrupt PSCM messages and trigger U0420 without any module being defective.
  • U0420 is sometimes stored alongside U0100 or U0126, and clearing those first can reveal whether the PSCM is the true source or just a victim of a network fault.
  • A software glitch in the PSCM can cause this code intermittently; reflashing the module often resolves it without part replacement.

Can I keep driving with U0420?

If the steering feels normal, you can drive cautiously to a repair shop, but avoid high speeds and heavy steering maneuvers. If the steering assist is lost or intermittent, stop driving and have the vehicle towed, as sudden loss of power steering can be dangerous.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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