Chevrolet U0420 Code – Resolving Invalid Data From Power Steering

The Chevrolet U0420 code indicates a communication fault where your vehicle’s control modules are receiving invalid data from the power steering system. This often triggers warning lights for your stability control or ABS, requiring a methodical check of the CAN bus network and sensor signals.

You are cruising down a mountain pass or navigating a busy city street when suddenly, your dashboard lights up like a Christmas tree. Your Electronic Stability Control (ESC) light turns on, and your power steering feels slightly different—or maybe it shuts off entirely.

If you hook up an OBD-II scanner and see a chevrolet u0420 code, you are dealing with a communication breakdown. This code specifically points to “Invalid Data Received from Power Steering Control Module.” It means your car’s brain (the PCM or BCM) is confused because it isn’t getting the reliable information it expects from the steering system.

In this guide, we will break down why this happens and how you can approach the diagnosis like a pro. Whether you are a weekend DIYer or a seasoned mechanic, understanding the digital handshake between modules is key to clearing this fault.

Understanding the Chevrolet U0420 Code Mechanics

At its core, the chevrolet u0420 code is not a mechanical failure of the steering rack itself, but a digital communication error. Modern vehicles use a complex network called a CAN bus to share data between modules in milliseconds.

When the Power Steering Control Module (PSCM) sends data that is garbled, out of range, or simply missing, the receiving module—usually the Electronic Brake Control Module or the Engine Control Module—logs this U-series code. Because the vehicle cannot verify the steering input, it defaults to a safety mode to prevent erratic handling.

This is why you might see secondary lights for your ABS or traction control. The car is effectively saying, “I don’t know what the steering wheel is doing, so I am disabling these stability features to stay safe.”

Common Symptoms of a Communication Fault

Before you grab your multimeter, look for these specific behaviors. Recognizing them helps you confirm that the chevrolet u0420 code is the primary culprit rather than a standalone sensor failure.

• Dashboard Warning Lights: The ESC, ABS, and power steering service lights are the most common indicators.
• Variable Steering Effort: You might notice the steering feels heavier than usual or loses the “assist” feel at low speeds.
• Cruise Control Disabling: Many vehicles will automatically disable cruise control when they detect a fault in the steering or stability systems.
• Erratic Data on Scan Tool: If you have a professional-grade scanner, you might see “Invalid” or “Data Error” when looking at live steering angle sensor (SAS) values.

Step-by-Step Diagnostic Approach

Don’t rush to replace expensive modules just yet. Most U-series codes are caused by simple wiring or voltage issues rather than a fried computer.

1. Check Your Battery and Charging System

Low voltage is the silent killer of sensitive electronic modules. If your battery is weak or your alternator is failing, the CAN bus network can become unstable, causing modules to “misinterpret” data. Ensure your system voltage is steady at 12.6V when off and 13.5V-14.5V when idling. For more on handling electrical gremlins, check out our guide on troubleshooting low system voltage.

2. Perform a Wiring Harness Continuity Test

Inspect the wiring harness leading to the power steering module. Look for signs of chafing, rodent damage, or corrosion at the connectors. A high-resistance connection can corrupt the data signal. Use a digital multimeter to check for continuity between the module and the main communication bus.

3. Perform a BCM Interrogation

The Body Control Module (BCM) often acts as a gateway for vehicle communications. Using a capable scan tool, interrogate the BCM to see if there are other related codes. If you see multiple communication codes (U-codes), focus on the power source and ground connections for the entire network.

Diagnostic Decision Flow

Use this simple decision matrix to determine your next move when facing the chevrolet u0420 code.

Observation	Likely Cause	Action
Battery voltage below 12V	Low System Voltage	Load test battery; check alternator.
Corroded/Loose Connector	Physical Connection	Clean terminals; inspect wiring harness.
Code persists with stable voltage	Internal Module Failure	Test/Replace Steering Column Control Module.

Addressing the Steering Column Control Module (SCCM)

If the wiring and voltage check out, the issue often resides in the Steering Column Control Module (SCCM). This component is responsible for processing inputs from the steering angle sensor and sending that data to the rest of the vehicle.

Replacing the SCCM is a more involved task that requires careful handling of the steering wheel and airbag assembly. Always disconnect the battery and wait at least 15 minutes before touching any airbag-related components. Safety is non-negotiable when working on steering systems.

Once replaced, you may need a specialized scan tool to perform a “steering angle sensor calibration.” Without this reset, the car won’t know the center position of the steering wheel, and the code will likely return immediately.

Frequently Asked Questions About The Chevrolet U0420 Code

Can I keep driving with this code active?

While you might be able to drive, it is not recommended. Because the code often disables stability control and ABS, your vehicle’s ability to handle emergency maneuvers is severely compromised. Get it diagnosed as soon as possible.

Is the U0420 code always a bad sensor?

No. In fact, it is rarely just a “bad sensor.” It is usually a communication error caused by poor wiring, a bad ground, or a module that has lost its calibration due to a voltage spike.

Do I need to visit a dealership for this repair?

Not necessarily. If you have a high-quality scan tool that supports bi-directional communication, you can perform most of the diagnostics yourself. However, if the fix requires a module replacement that needs programming to the vehicle’s VIN, you may need to visit a shop with proper factory software access.

Does this affect my power steering fluid?

Most modern Chevrolet vehicles with this code use Electric Power Steering (EPS). There is no fluid to check. If your vehicle uses a traditional hydraulic system, check for leaks, but know that the U0420 code is purely electronic in nature.

Final Thoughts for the DIY Enthusiast

Dealing with a chevrolet u0420 code requires patience and a methodical approach. It is easy to get frustrated when dealing with invisible digital signals, but by focusing on the basics—voltage, grounds, and physical connections—you can often solve the issue without breaking the bank.

Always document your steps and keep your scan tool data saved. If you find yourself in over your head, don’t hesitate to reach out to a professional mechanic. Your steering and stability systems are vital for your safety on the road or the trail. Stay safe, take your time with the wiring, and keep those wheels turning!