Honda U0122 Trouble Code Meaning, Causes & Symptoms Explained

If your Honda’s check engine light is on and the scanner shows a U0122 code, you’re likely feeling a bit confused. This guide explains the Honda U0122 trouble code meaning, causes, and symptoms so you can understand what your car is telling you.

It’s a communication problem inside your vehicle’s network. Don’t worry, we’ll break it down into simple terms and give you a clear path to a fix.

The U0122 code is a generic diagnostic trouble code (DTC) that stands for “Lost Communication with Vehicle Dynamics Control Module.” In simpler terms, it means the main computer in your Honda (the PCM or ECM) has lost its electronic conversation with the Vehicle Stability Assist (VSA) module.

Your modern car is like a small network of computers talking over wires. When one computer stops chatting, the others notice and log a code. The VSA module is crucial for safety systems like stability and traction control.

What Does the VSA Module Do?

The Vehicle Stability Assist module is a key safety component. It constantly monitors your steering angle, wheel speed, and lateral movement. Its job is to help prevent skids and loss of control.

When it detects a problem, it can apply brakes to individual wheels and even reduce engine power to help you steer the vehicle. Without proper communication with this module, these systems may not work correctly.

Common Symptoms of a U0122 Code

You might notice one or more of these signs when this code is active. The most obvious one is warning lights on your dashboard.

The Check Engine Light is illuminated (solid).
The VSA/ABS warning lights are on, often amber in color.
Stability Control (VSA) and Traction Control systems are disabled. You may see a “VSA Off” message.
The anti-lock brake system (ABS) may also be disabled.
In some models, the power steering may feel heavier or an EPS light may come on.
Cruise control may not function.

Is It Safe to Drive With a U0122 Code?

This is a serious question. While your car will likely still drive, your important safety systems are compromised. You won’t have stability or traction control assistance.

Driving in wet, snowy, or slippery conditions is riskier. You should address the issue promptly. Avoid aggressive driving and get the problem diagnosed as soon as you reasonably can.

Primary Causes of the U0122 Code in Hondas

The root cause is always a break in communication. Finding where that break happened is the key to fixing it. Here are the most common culprits, starting with the simplest.

1. Low Battery Voltage or a Weak Battery

This is perhaps the most frequent cause of random network communication codes. Modern vehicle computers are sensitive to voltage.

A weak battery, poor connections, or a failing alternator can cause voltage drops. These drops can momentarily reset modules, interrupting communication and setting a U0122.

2. Blown Fuse or Faulty Relay

The VSA module has its own power circuit. A blown fuse in the engine bay or interior fuse box will cut power to the module entirely.

Always check the fuse first—it’s easy and cheap. Refer to your owner’s manual for the exact fuse location for the VSA or ABS system.

3. Problems with the CAN Bus Network

The Controller Area Network (CAN bus) is the communication wiring that links all the modules. Physical damage to these wires is a common cause.

Wires chewed by rodents in the engine bay.
Wires damaged from chafing or heat near the exhaust.
Corroded or loose connectors at the VSA module or PCM.
Water intrusion into a connector, especially after driving in heavy rain.

4. A Faulty VSA Modulator-Control Unit

The VSA module itself can fail internally. This is less common than wiring issues but does happen. The module is typically located in the engine bay, often near the master brake cylinder.

It’s a sealed unit containing valves and sensors. Physical damage or internal electronic failure will require replacement of the unit, which then needs to be properly calibrated.

5. Issues with Other Connected Modules

Sometimes the problem isn’t with the VSA module directly. A failure in another module on the same network, like the steering angle sensor or the PCM itself, can disrupt the entire conversation and cause a U0122 code to be set.

How to Diagnose a U0122 Code: A Step-by-Step Guide

Here is a logical order to approach the diagnosis. You’ll need a basic scan tool and a multimeter for some steps.

Start with a Full Scan: Read all codes from every module (PCM, ABS/VSA, SRS, etc.). Other codes can provide clues about where the network problem started.
Check Battery Health: Measure battery voltage with the engine off (should be ~12.6V) and with it running (should be 13.5-14.8V). Clean any corrosion from battery terminals.
Inspect Fuses: Locate and visually inspect all fuses related to the ABS, VSA, and ECU/ECM systems. Use a multimeter to check for continuity to be sure.
Perform a Visual Inspection: Look for obvious wire damage, especially in the engine bay and near the VSA module. Check connectors for corrosion or bent pins.
Check for Live Data: If your scan tool can access it, look at live data from the PCM. See if it recognizes steering angle sensor data or other VSA parameters. If it does, communication might be intermittent.
Test CAN Bus Wiring: With a multimeter, you can check the resistance of the CAN bus network (at the diagnostic port) or for proper voltage levels on the CAN High and CAN Low wires. This requires a wiring diagram.
Module Power and Ground Test: Find the wiring diagram for your specific Honda model. Test at the VSA module connector to confirm it has constant power, switched power, and a good ground.

Repair Procedures and What to Expect

The repair depends entirely on what you find during diagnosis. Here are the common fixes.

Fixing Simple Electrical Issues

If you find a blown fuse, replace it with one of the same amperage. If it blows again, you have a short circuit downstream that needs to be found.

For corroded connectors, use electrical contact cleaner and a small brush to clean the terminals. Ensure the connector clicks securely into place. For damaged wires, solder and heat-shrink tubing is the proper repair method—never just use electrical tape.

Replacing the VSA Modulator-Control Unit

This is a significant repair. The unit is expensive and requires bleeding the brake system. After installation, a specific calibration procedure must be performed using a professional-grade scan tool.

This calibration often involves turning the steering wheel lock-to-lock and driving the vehicle in a straight line. This is typically a job for a professional mechanic with the right equipment.

Addressing PCM or Other Module Failures

If the Powertrain Control Module itself is faulty, it may need to be replaced or reprogrammed. This is rare. A specialist should confirm this diagnosis, as PCMs are costly.

Estimated Repair Costs

Costs vary wildly based on the cause and labor rates in your area.

Fuse Replacement: Less than $10 if you do it youself.
Wiring Repair: $100 – $400, depending on how hard the wire is to access.
VSA Module Replacement: $800 – $1,500+ for parts. Labor adds another $200 – $400. Calibration is key.
Professional Diagnosis: Expect 1-2 hours of labor ($100 – $250) just for the diagnosis, which may be applied to the repair cost.

Preventing a U0122 Code from Returning

While you can’t prevent all electrical failures, you can reduce the risk.

Maintain your battery. Replace it every 4-5 years or when it shows signs of weakness.
Address rodent issues if you see signs of them in your garage or engine bay.
Fix any water leaks into the cabin or engine bay promptly, as moisture leads to corrosion.
Avoid spraying high-pressure water directly at engine bay connectors when washing the engine.

FAQ: Honda U0122 Code Questions

Can I clear the U0122 code myself?

Yes, you can clear it with an OBD2 scanner. However, if the underlying problem isn’t fixed, the code and warning lights will come back, usually within one or two drive cycles. Clearing the code will not reactivate the VSA system if the fault is still present.

Will a U0122 code fail my state’s emissions test?

In most states, yes. An illuminated Check Engine Light (MIL) is an automatic failure for an emissions inspection. Even if the car seems to run fine, you’ll need to get the code resolved and the light off to pass.

Is the VSA module the same as the ABS module?

In most modern Hondas, they are integrated into one unit called the VSA Modulator-Control Unit. It handles both the anti-lock braking and the vehicle stability assist functions. So when it fails, both systems are typically affected.

Could a recent repair or service have caused this code?

Absolutely. If work was done recently, a connector might not have been plugged back in all the way. Or a fuse might have been left out. Always double-check work areas after any service, especially involving the brakes, suspension, or electrical system.

My Honda has a U0122 and is in limp mode. Why?

Some Honda models may limit engine performance or shift patterns when a critical network fault is detected. This is a safety precaution. Fixing the U0122 communication fault should resolve the limp mode condition.

Final Thoughts on the U0122 Code

The Honda U0122 trouble code points to a loss of communication with a major safety system. While diagnosis can seem daunting, following a logical process from simple to complex will often reveal the cause.

Start with the battery and fuses, then move to a careful visual inspection. For many DIYers, finding a chewed wire or loose plug is a fix they can handle. For issues involving module replacement or complex wiring faults, seeking a qualified technician, especially one familiar with Honda systems, is a wise investment in your safety.

Remember, driving without functioning stability control changes how the vehicle handles in an emergency. Getting this code fixed restores your Honda’s full suite of safety features and gives you peace of mind on the road.