What it means
Other modules receive implausible EPS torque or angle data. EPS reduces or disables assist; the EPS warning lamp comes on.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
The power steering control module shares electric power steering torque and steering angle information with other modules over the vehicle network. U0521 sets when a receiving module rejects that information as implausible; the steering module may reduce or disable assist.
Common causes
Most likely first.
- Torque sensor drift
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan the power steering module and all other modules, saving freeze-frame data and related steering or network codes before clearing anything.
- Check the steering warning lamp and compare steering effort while stationary and moving slowly in a safe area, since reduced assist can make the wheel much harder to turn.
- Inspect the power steering module connectors, steering torque sensor wiring, and network wiring for damage, looseness, corrosion, or water intrusion.
- Use a scan tool to compare live torque and angle data with steering input and check whether the implausible value originates at the steering module or appears downstream.
- Have a technician test network communication and gateway routing, and verify any suspected network termination fault against the manufacturer's specification.
Common fixes
- Repair damaged or corroded power steering or network wiring and connectors.
- Correct module configuration or software compatibility if the fault followed a module replacement.
- Repair gateway routing if network tests show steering data is being misrouted.
- Repair or replace the torque sensor or power steering control module if testing confirms its data is faulty.
- Repair a network termination fault if measurements are outside the manufacturer's specification.
Can I keep driving?
If steering assist is reduced or the steering warning lamp is on, avoid unnecessary driving because the wheel may take much more effort to turn, especially at low speed. Stop safely if steering control is impaired and arrange inspection before continuing.
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.