U3021 severity depends on the affected system. While some communication errors are intermittent, others can cause system failures. Professional diagnosis is recommended.

Can I drive with U3021?

Short trips may be possible depending on which system is affected. However, if warning lights are on or vehicle behavior is abnormal, have it inspected before driving.

Will U3021 clear itself?

U3021 may clear if the fault is intermittent, but it will likely return if the underlying wiring or module issue is not resolved. Use a scan tool to monitor pending and confirmed codes.

U3021 - Control Module Input Power C Circuit Low

U3021 is a Diagnostic Trouble Code (DTC) in the Network Communication (U) category. It indicates control module input power c circuit low. These codes relate to the vehicle's onboard communication network (CAN bus, LIN bus, etc.) and module-to-module data exchange. When U3021 is set, it means one or more control modules have detected a communication fault, data integrity issue, or software incompatibility on the vehicle network.

U3021 - Control Module Input Power C Circuit Low

What is U3021?

U3021 is a Diagnostic Trouble Code (DTC) in the Network Communication (U) category. It indicates control module input power c circuit low. These codes relate to the vehicle's onboard communication network (CAN bus, LIN bus, etc.) and module-to-module data exchange.

When U3021 is set, it means one or more control modules have detected a communication fault, data integrity issue, or software incompatibility on the vehicle network.

Common Symptoms

Module not powering on
Intermittent module operation
Low voltage warnings
Multiple module failures
Battery drain issues

Possible Causes

Blown fuse
Open power feed wire
Corroded power connection
Faulty ignition switch
Battery voltage issues

Step-by-Step Diagnosis

Connect a professional-grade OBD2 scanner and check for all active and pending U-codes.
Identify which modules are communicating and which are not.
Check power, ground, and communication wiring for the Control Module Input Power C Circuit Low using a wiring diagram.
Perform a voltage drop test on power and ground circuits to the affected module.
Check CAN bus resistance (should be ~60 ohms between CAN-High and CAN-Low).
Use a scan tool to monitor live data from modules that are still communicating.
Perform a wiggle test on wiring harnesses while monitoring for communication recovery.
If a module replacement is suspected, verify correct part number and programming requirements.
Clear codes and retest after repairs.

Recommended Repairs

Repair any damaged wiring, connectors, or terminals. Ensure proper routing and secure mounting.
Clean corroded connector pins with electrical contact cleaner.
Replace blown fuses and verify correct amperage rating.
If a module requires programming, ensure it is done with the correct software version.
Update or reflash module software if a TSB applies.
Replace failed control module if testing confirms internal failure.
Verify all repairs by checking module communication with a scan tool.

Related Diagnostic Trouble Codes

External References and Forum Discussions

Disclaimer

The information provided is for educational purposes only. Always consult a qualified mechanic or dealership for accurate diagnosis and repair. U-codes often require specialized diagnostic tools and access to manufacturer-specific wiring diagrams and software.

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U3021 - Control Module Input Power C Circuit Low

U3021 — Codice di guasto