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U0426 — Invalid Data Received From Vehicle Immobilizer Control Module

Generic OBD-II · all makesNetwork / communication

OBD-II code U0426 indicates that the vehicle's primary computer (PCM/ECM) has received invalid or corrupted data from the immobilizer control module. This communication error can prevent the engine from starting or cause intermittent security-related issues.

Symptoms

What causes it — most likely first

1. Faulty immobilizer control module

The immobilizer module itself may be malfunctioning, sending incorrect or no data to the PCM. This is a common cause, especially in vehicles with high mileage or exposure to moisture.

2. Wiring or connector issues between the immobilizer module and PCM

Damaged, corroded, or loose wiring or connectors in the communication circuit can disrupt data transmission. This includes chafed wires, poor grounds, or water intrusion.

3. Failed or weak key transponder

The key fob or transponder may be damaged or demagnetized, causing the immobilizer module to send invalid data. This is often overlooked but frequently the root cause.

4. Incorrect or aftermarket key programmed incorrectly

If a new or aftermarket key was recently programmed, it may not be properly synchronized with the immobilizer module, leading to invalid data errors.

5. CAN bus or network communication issues

Problems with the vehicle's Controller Area Network (CAN) bus, such as shorts, opens, or high resistance, can corrupt data between modules, including the immobilizer.

6. PCM/ECM failure (rare)

While uncommon, a faulty PCM/ECM could misinterpret or fail to process data from the immobilizer module. This is typically a last-resort diagnosis after all other causes are ruled out.

How it's diagnosed

  1. Scan for additional codes in the immobilizer module and other related modules (e.g., PCM, instrument cluster) to identify patterns or related faults.
  2. Inspect the wiring and connectors between the immobilizer module and PCM for damage, corrosion, or loose connections. Pay attention to ground circuits and CAN bus integrity.
  3. Test the key transponder with a known-good key or a diagnostic tool capable of reading transponder data. Verify the immobilizer module recognizes the key correctly.
  4. Check for proper power and ground supply to the immobilizer module. Use a multimeter to verify voltage and ground integrity at the module connector.
  5. If wiring and keys are confirmed good, test the immobilizer module itself using a diagnostic tool to verify its functionality. Replace if faulty.
  6. As a last step, reflash or replace the PCM/ECM if all other causes are exhausted, but only after confirming the immobilizer module and network are functioning correctly.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0420 — Invalid Data Received From Power SteerU0421 — Invalid Data Received From Suspension U0422 — Invalid Data Received From Body ControU0423 — Invalid Data Received From Instrument U0424 — Invalid Data Received From Hvac ControU0425 — Invalid Data Received From Auxiliary H

Frequently asked

Is the PCM/ECM usually the cause of U0426?

No, the PCM/ECM is rarely the cause of U0426. This code typically stems from issues with the immobilizer module, wiring, or key transponder. Replacing the PCM/ECM should only be considered after all other potential causes have been thoroughly ruled out.

Can I drive with U0426 present?

Driving with U0426 is not recommended. The vehicle may start intermittently or not at all, and stalling could occur unexpectedly, posing a safety risk. Diagnose and repair the issue as soon as possible.

Why does my car start sometimes but not others with this code?

Intermittent starting issues with U0426 are often caused by loose or corroded wiring, a weak key transponder, or a failing immobilizer module. These issues can cause sporadic communication failures between the immobilizer and PCM.

Do I need a special tool to diagnose U0426?

A basic OBD-II scanner may not be sufficient. A more advanced diagnostic tool capable of reading immobilizer module data and testing transponder keys is often required to pinpoint the exact cause.