What it means
A control module received data from the Power Steering Control Module that it judged invalid or implausible. This code does not establish that steering assist is reduced or disabled.
At a glance
- Usually lights the warning light of the system that lost communication
How it works
The Power Steering Control Module manages or reports steering-assist functions and related operating data. U0420 sets when another module rejects data from the power steering module as implausible; the code alone does not show that steering assist has been lost.
Common causes
Most likely first.
- Fault or implausible input at the Power Steering Control Module
- Damaged or loose network wiring or connector
- Module power, ground, or programming issue
Symptoms
- Power-steering warning message
- Steering-related functions may be limited
- Other communication codes
How to diagnose it
- Scan all modules and save freeze-frame and related steering or network codes to see whether the event coincided with a wider communication or voltage fault.
- Check for a power-steering warning and assess whether steering effort or steering-related functions have changed.
- Inspect the power steering module connector and wiring for looseness, corrosion, water entry, or damage.
- Check module power and ground circuits to the manufacturer's specification, since a supply fault can affect reported steering data.
- Compare live steering module data with related vehicle data and test network communication and module circuits to the manufacturer's specification.
- If the network and circuits pass, check for applicable software or calibration updates before considering module replacement.
Common fixes
- Secure or repair the power steering module connector.
- Repair damaged network wiring to the module.
- Correct power or ground faults at the module.
- Apply an applicable software or calibration update.
- Replace the power steering control module if its inputs and circuits test correctly but its data remains invalid.
Can I keep driving?
If steering effort changes, a steering warning appears, or control feels uncertain, slow down and stop safely; do not continue until the steering system is checked. If steering feels normal, drive cautiously to a repair location and watch for changes.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.