U0420 — Invalid Data Received From Power Steering Control Module

Generic OBD-II · all makesNetwork / communication

The U0420 code indicates that a control module on the vehicle's communication network has received invalid data from the Power Steering Control Module (PSCM). This typically means the PSCM is sending corrupted or implausible information, which can affect power steering operation and trigger warning lights. The issue is usually caused by a fault within the PSCM itself, wiring problems, or low system voltage.

Symptoms

Illuminated check engine light
Power steering warning light on
Loss or reduction of power steering assist
Increased steering effort, especially at low speeds
Other warning lights (e.g., ABS, traction control) may illuminate
No noticeable symptoms other than the warning light

What causes it — most likely first

1. Faulty Power Steering Control Module (PSCM)

Internal failure of the PSCM is the most common cause, leading to corrupted or invalid data being sent over the CAN bus.

2. Damaged or corroded wiring/connectors

Wiring harness issues, loose or corroded connectors at the PSCM, or damaged CAN bus wiring can disrupt communication.

3. Low battery voltage or charging system problem

A weak battery or failing alternator can cause voltage drops that make modules send invalid data.

4. Faulty steering angle sensor

If the steering angle sensor is integrated with or provides data to the PSCM, a fault in the sensor can cause the PSCM to transmit invalid information.

5. Software incompatibility or calibration issue

After module replacement or reprogramming, incorrect software or calibration can lead to invalid data being sent.

6. Faulty engine control module (PCM) or other receiving module

Rarely, the module interpreting the data may have an internal fault, but this is the least likely cause and should only be considered after all other possibilities are ruled out.

How it's diagnosed

Use a scan tool to check for other diagnostic trouble codes, especially communication codes (U-codes) and power steering related codes. Address any additional codes first.
Inspect the power steering control module connectors and wiring for damage, corrosion, or loose connections. Pay close attention to the CAN bus wiring.
Check battery voltage and charging system output. Ensure the battery is fully charged and the alternator is functioning properly.
Use a scan tool capable of reading live data from the PSCM to verify communication and check for implausible values (e.g., steering angle, torque sensor).
Perform manufacturer-specific diagnostic tests for the power steering system, which may include checking power and ground at the PSCM and testing CAN bus resistance.
If all other tests pass and the PSCM is suspected, follow the manufacturer's procedure for module replacement and programming.

Code facts & related codes

SystemNetwork / communication

StandardizationSAE generic — identical on every make

Frequently asked

Can I drive my vehicle with a U0420 code?

It may be possible to drive, but it is not recommended. The power steering assist may be reduced or disabled, making the vehicle harder to control, especially at low speeds. This can be a safety risk.

Does a U0420 code mean I need to replace the PCM?

Almost never. The U0420 code is often misinterpreted as a PCM fault, but the PCM is simply reporting invalid data from the power steering module. The root cause is almost always the power steering module itself, wiring, or a voltage issue. Replacing the PCM is a very expensive and rarely effective fix.

Can a weak battery cause a U0420 code?

Yes, a weak battery or charging system problem can cause voltage drops that lead to communication errors and invalid data. Always check the battery and alternator before replacing any modules.

What should I check first when diagnosing U0420?

Start by checking for other codes, then inspect the power steering module connectors and wiring for damage or corrosion. Verify battery voltage and charging system health. These simple checks often reveal the problem.