U0420 — Power steering module sending invalid data on network

The car’s computer is receiving incorrect or corrupted information from the power steering control module. This usually happens due to communication errors between modules, wiring issues, or a failing power steering control unit.

Common causes

The cause is almost always one of a few things. Here they are — U0420 rarely comes from anything outside this list:

• Faulty power steering control module
• Damaged or corroded wiring/connectors in steering system
• Interference or communication errors on vehicle network
• Software glitches or outdated module programming

Where to start

In the order a sensible mechanic would work — the cheap checks first, the expensive replacements only after:

1. Check and clean wiring connectors at power steering module
2. Inspect wiring harness for damage or corrosion
3. Update or reflash power steering module software
4. Replace power steering control module if faults persist

That is what holds for U0420 in general. From here it depends on your engine — tell me which car it is and what it does, and I will give you the steps for it: real procedures, torque figures and diagrams instead of general advice.