U0420 — Invalid Data Received – Power Steering Control Module #

Note: The description for this Diagnostic Trouble Code (DTC) may vary depending on the vehicle manufacturer (OEM). Always consult your OEM service documentation for the most accurate definition.

• “Invalid Data Received From Power Steering Control Module” (General Motors, Ford, FCA/Stellantis)
• “Invalid Data Received from EPS Control Module” (Toyota, Honda, Subaru)
• “Incorrect Data Received from Steering Assist Module” (Volkswagen/Audi, BMW)

Summary of Code U0420 #

DTC U0420 indicates that a communication issue has occurred between a control module—typically the main vehicle computer, or Powertrain Control Module (PCM)—and the Power Steering Control Module (PSCM). The code means the data being exchanged is either missing, incomplete, or doesn’t follow the expected format. This communication happens over a network known as the Controller Area Network (CAN) bus, which acts like the digital nervous system of your vehicle. When the information sent from the power steering module doesn’t make sense or can’t be verified, the system triggers U0420 to alert the driver or technician of a potential issue. While this code usually does not pinpoint the exact faulty part, it’s a strong indicator of a communication breakdown that could affect steering performance and overall vehicle safety.

Common Symptoms for Code U0420 #

You might notice several warning signs when your vehicle registers the U0420 DTC. These symptoms can vary in severity, but they often revolve around steering performance and dashboard alerts. Sometimes, they’re subtle—other times, they’re hard to miss.

• Illuminated power steering or general warning light on the dashboard
• Heavier than usual steering effort (loss of power assist)
• Intermittent or complete loss of power steering assist
• “Service Power Steering” or “Check Steering System” messages
• Steering feels jerky or inconsistent
• Other communication-related codes stored (U-codes)

Most Likely Causes for Code U0420 #

The U0420 code can be triggered by a variety of issues, but they tend to fall into a few common categories. Understanding these helps you prioritize your diagnosis and avoid chasing red herrings. Here are the most frequent culprits, ranked in likely order:

1. Faulty Power Steering Control Module (PSCM)—the module itself is not transmitting correct or valid data.
2. Wiring or connector problems—damaged, corroded, or loose CAN bus wiring/connectors between the PSCM and other modules.
3. CAN bus network issues—interference, shorts, or opens in the communication lines.
4. Software or programming errors—the PSCM or other network modules have outdated, corrupted, or mismatched software.
5. Battery or power supply problems—low voltage or unstable power can disrupt communication.
6. Other faulty modules—sometimes, a different module sends bad data, which gets blamed on the power steering system.

Step-by-Step Diagnostic Guide for U0420 #

Properly diagnosing a U0420 code involves methodical troubleshooting, as communication issues can be tricky to pinpoint. Here’s a practical, step-by-step plan to tackle this DTC:

• 1. Scan all modules: Use a professional scan tool to check for additional codes in all modules, not just the power steering system.
• 2. Verify power and grounds: Confirm the PSCM has proper battery voltage and solid ground connections.
• 3. Inspect CAN bus wiring: Visually and electrically inspect CAN bus wires and connectors for damage, corrosion, or loose pins—especially at the PSCM.
• 4. Check software versions: Make sure all related modules have the latest OEM software updates. Look for technical service bulletins (TSBs).
• 5. Test PSCM operation: If possible, use a scan tool to communicate directly with the PSCM. Check for live data and bidirectional controls.
• 6. Perform a network integrity test: Use a scope or scan tool to check CAN network signal quality and resistance (typically 60 ohms across CAN-H and CAN-L with ignition off).
• 7. Substitute known-good module (if accessible): If all wiring and power checks out, try swapping in a known-good PSCM to confirm the diagnosis.

Potential Repairs for Code U0420 #

After identifying the root cause, repairs for a U0420 code should be precise and tailored to the specific fault. Here are common fixes, matched to the typical causes:

• Repair or replace damaged CAN bus wiring or connectors
• Clean and secure all power and ground connections at the PSCM
• Update or reprogram module software as per OEM guidelines
• Replace the Power Steering Control Module if confirmed faulty
• Address battery or voltage issues (replace battery, repair charging system, etc.)
• Repair or replace other malfunctioning modules that may disrupt network data

Is It Safe to Drive with Code U0420? #

Driving with a U0420 code is not recommended until the issue is diagnosed. In some cases, the vehicle may still steer, but you could lose power assist suddenly or intermittently, making steering much harder—especially at low speeds or during emergency maneuvers. Even if you don’t notice symptoms, a communication failure in the steering system is a safety risk that could escalate without warning. Always address this code promptly to avoid dangerous situations.

Vehicles Most Commonly Affected by U0420 #

While U0420 is a “generic” OBD-II code, it’s more frequently seen in certain vehicles—especially those with electric power steering (EPS) systems and complex CAN networks. Based on repair trends and manufacturer bulletins, the following vehicles are more likely to experience this code:

• Ford F-Series, Fusion, Escape, Explorer (2012+)
• Chevrolet Silverado, Equinox, Malibu (2014+)
• Chrysler 200, Dodge Charger, Jeep Grand Cherokee (2011+)
• Toyota Camry, RAV4, Prius (2015+)
• Honda Accord, Civic, CR-V (2014+)
• Volkswagen Jetta, Golf, Passat (2013+)
• BMW 3-Series, 5-Series (F30/G30 generation)

Common Mistakes and Best Practices for U0420 Diagnostics #

Misdiagnosing U0420 is easy if you rush the process or skip steps. Following best practices helps avoid unnecessary parts replacement and frustration:

• Don’t replace the PSCM without verifying power, ground, and network wiring integrity first.
• Always check for additional U-codes—these can point to larger network issues or other faulty modules.
• Don’t ignore Technical Service Bulletins (TSBs)—OEMs may have known fixes or updated software for this issue.
• Document all test results and steps for future reference or warranty claims.
• Be aware that aftermarket accessories (remote starters, alarms, etc.) can disrupt CAN communication and cause U0420.

Quick FAQ for U0420 #

If you’re facing a U0420 code, you likely have questions. Here are a couple of quick answers to common concerns:

• Q: Can a weak battery trigger U0420?
  A: Yes, low voltage can disrupt module communication and cause this code. Always test the battery and charging system as a first step.
• Q: Will clearing the code fix the problem?
  A: Clearing the code may make the warning light disappear temporarily, but if the underlying problem isn’t fixed, U0420 will return—sometimes even immediately.