U0099 Code: Lost Communication With a Control Module

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The U0099 diagnostic trouble code (DTC) indicates that communication between vehicle control modules has been interrupted over the Controller Area Network (CAN) bus. U0099 is a manufacturer-specific code, meaning the affected module varies by vehicle make and model.

What Does the U0099 Code Mean?

DTC U0099 is stored when a control module no longer receives expected CAN bus messages from another module for a specified period. This communication failure is commonly caused by wiring damage, loose connectors, low battery voltage, blown fuses, or an internal module fault.

Symptoms

  • Check Engine Light or warning indicator illuminated.
  • Communication failure with one or more control modules.
  • Certain electronic systems stop operating.
  • Instrument cluster warning messages.
  • Additional U-series communication DTCs stored.

Possible Causes

  • Open or short circuit in the CAN High or CAN Low network.
  • Loose, damaged, or corroded electrical connectors.
  • Low battery or charging system voltage.
  • Blown fuse supplying the affected module.
  • Defective control module.

Can You Drive With U0099?

Driving Severity: Moderate. The vehicle may remain drivable, but communication failures can disable important electronic systems. Diagnose the fault promptly to avoid additional problems.

Estimated Repair Cost

  • Fuse replacement: $10–40
  • Connector repair: $20–80
  • CAN wiring repair: $80–300
  • Control module programming: $100–250
  • Control module replacement: $300–1,200

Basic Diagnostic Steps

  1. Scan all vehicle modules for stored DTCs.
  2. Verify battery and charging system voltage.
  3. Inspect CAN bus wiring and connectors.
  4. Check power and ground circuits for the affected module.
  5. Repair wiring faults or replace the faulty module if necessary.

Related DTC Codes

U0099 may be accompanied by U0097, U0098, U0100, or U0140. Reviewing all communication-related DTCs together often leads to a faster and more accurate diagnosis.

Frequently Asked Questions

Is U0099 a generic OBD-II code?

No. U0099 is typically a manufacturer-specific communication code, and its exact definition depends on the vehicle manufacturer.

Can a weak battery cause U0099?

Yes. Low battery voltage or charging system problems can interrupt CAN bus communication and trigger U0099.

Should I replace the control module immediately?

No. Always inspect the battery, fuses, wiring, connectors, and module power and ground circuits before replacing any control module.

Conclusion

U0099 indicates a CAN bus communication failure between vehicle control modules. In many cases, repairing damaged wiring, restoring proper power and ground, or fixing connector issues resolves the problem without replacing expensive electronic modules.

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