U0118

Universal

Lost Communication With Fuel Additive Control Module

Definition source: General OBD-II reference catalog
Definition verification: Not independently verified for display.
Time: Varies by diagnosis and vehicle | Diagnostic difficulty: Medium
Medium Severity

The vehicle has detected that one or more control modules are not receiving expected messages from the fuel additive control module. On vehicles equipped with this system, the module manages or monitors fuel additive delivery, which may support emissions or aftertreatment operation. The code identifies a communication problem, not proof that the module itself has failed.

Report an error with this code

⚠️ Before You Begin (Safety First)

If the vehicle drives normally and no serious warnings are present, this code alone does not necessarily mean you must stop driving. Follow any dashboard warnings and stop safely if the vehicle develops severe loss of power, stalls, overheats, or shows another urgent warning. Have emissions or aftertreatment warnings checked promptly.

Common Symptoms

  • There may be no noticeable symptoms if the communication interruption is brief or the vehicle does not rely on the system for an active function.
  • A check-engine, emissions, or system warning may appear because a control module has detected missing messages.
  • If the vehicle uses additive-assisted emissions or aftertreatment functions, those functions may be limited or unavailable while communication is lost.
  • Other communication codes may appear if the cause affects a shared network, power supply, or ground.

Common Causes

  • A loose, damaged, corroded, or wet connector at the fuel additive control module or along its wiring.
  • An open, shorted, or otherwise damaged network wire preventing messages from reaching the module.
  • A blown fuse or an issue with the module's power supply or ground.
  • Low vehicle voltage or another electrical problem disrupting module communication.
  • A fault inside the fuel additive control module; the code alone does not confirm this cause.

Diagnostic Steps

  1. Check the owner's manual for any warning-light guidance and note whether the vehicle has drivability or emissions symptoms.
  2. With the vehicle safely parked and switched off, look for visible damage, moisture, or loose connections at accessible wiring and connectors related to the system. Do not unplug connectors unless the vehicle-specific instructions say it is safe.
  3. Check only the relevant fuses identified in the owner's manual. Replace a failed fuse only with the specified type and rating; if it fails again, seek diagnosis rather than repeatedly replacing it.
  4. If a scan tool is available, record all codes from all modules before clearing anything. Related communication or voltage codes can help identify a shared electrical or network problem.
  5. If the code returns, or wiring, fuse, or module testing is needed, arrange vehicle-specific diagnosis. Avoid probing network circuits without the correct wiring information and test procedure.

When to Call a Professional

Check for related communication and low-voltage codes across all modules before replacing parts. A technician can verify the fuel additive control module's power and ground, inspect its connectors and network wiring, and determine whether other modules can communicate with it. Module replacement, if ultimately needed, may require vehicle-specific setup or programming.

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Commonly Asked Questions

Does U0118 prove that the fuel additive control module is faulty?

No. It indicates lost communication with that module. Wiring, connectors, power, ground, low voltage, or a network problem can cause the same condition.

Can I drive with U0118?

It depends on the vehicle's symptoms and warnings. If it drives normally, the code alone may not require an immediate stop, but follow dashboard instructions and arrange diagnosis, especially if an emissions or aftertreatment warning is present.

Why might there be no noticeable symptoms?

A brief interruption or a system that is not currently needed may not change how the vehicle feels. The code can still indicate that a control module missed expected messages.

What should be checked before replacing the module?

Check other module codes and verify the module's power, ground, connectors, and network wiring using procedures for the specific vehicle. Replacement should follow evidence that the module itself is not communicating despite those checks.

Browse Available Code Guides

Previous and next available guides in database record order, across makes. Adjacent entries may share a code number and do not necessarily describe related faults.