The U0118 Diagnostic Trouble Code (DTC) indicates that communication has been lost with the Fuel Additive Control Module (FACM) through the High-Speed Controller Area Network (HS-CAN). This communication failure prevents other electronic control modules from exchanging important fuel additive system information, which may affect emissions control, engine performance, and diagnostic capabilities.
Modern vehicles equipped with diesel exhaust aftertreatment systems or fuel additive injection systems rely on continuous communication between multiple electronic modules. The Engine Control Module (ECM), Body Control Module (BCM), Transmission Control Module (TCM), ABS Module, Instrument Cluster, and Fuel Additive Control Module constantly exchange CAN Bus messages. When communication with the Fuel Additive Control Module stops, the network detects the interruption and stores Diagnostic Trouble Code U0118.
Unlike performance-related fuel additive codes, U0118 is strictly a communication fault. The root cause is typically damaged CAN Bus wiring, poor power or ground connections, connector corrosion, low battery voltage, or an internal failure of the Fuel Additive Control Module.
What Does U0118 Mean?
U0118 means that one or more control modules can no longer communicate with the Fuel Additive Control Module over the High-Speed CAN Bus network. As communication is lost, the Engine Control Module may disable fuel additive functions and activate emission-related fail-safe strategies.
On diesel vehicles equipped with diesel particulate filters (DPF), selective catalytic reduction (SCR), or fuel-borne catalyst systems, this communication failure may affect regeneration performance, emission efficiency, and warning lamp operation.
How the Communication Network Operates
During normal operation, the Fuel Additive Control Module exchanges information related to additive quantity, pump operation, system status, and diagnostic information with the Engine Control Module. When communication stops, the network immediately recognizes the fault and stores U0118.
Modules That Communicate With the Fuel Additive Control Module
| Module | Function |
|---|---|
| Engine Control Module (ECM) | Controls fuel additive strategy |
| Fuel Additive Control Module (FACM) | Monitors additive pump and dosing |
| Body Control Module (BCM) | Network communication management |
| Transmission Control Module (TCM) | Coordinates operating conditions |
| Instrument Cluster | Displays emission warnings |
| Diagnostic Scan Tool | Reads live additive system data |
Symptoms of U0118 Code
The symptoms of U0118 depend on the vehicle manufacturer and the type of fuel additive system installed. Vehicles equipped with diesel particulate filter (DPF), SCR, or fuel-borne catalyst systems may experience emission-related warnings and reduced regeneration performance.
| Symptom | Severity |
|---|---|
| Check Engine Light (MIL) | ★★★★★ |
| Emission System Warning | ★★★★★ |
| DPF Regeneration Failure | ★★★★★ |
| Reduced Engine Performance | ★★★★☆ |
| Limp Mode Activated | ★★★★☆ |
| Poor Fuel Economy | ★★★☆☆ |
| Additional U-Codes Stored | ★★★★☆ |
Common Causes of U0118
U0118 is usually caused by a communication interruption rather than a defective fuel additive pump or additive injector.
- Open circuit in CAN High wiring.
- Open circuit in CAN Low wiring.
- Short to ground on CAN Bus circuits.
- Short to battery voltage.
- Loose or corroded Fuel Additive Control Module connector.
- Blown fuse supplying the Fuel Additive Control Module.
- Poor chassis or module ground connection.
- Low battery or charging system voltage.
- Damaged wiring harness near the fuel tank or additive reservoir.
- Internal failure of the Fuel Additive Control Module.
How Serious Is U0118?
The U0118 communication fault should be considered serious, especially on diesel vehicles that rely on the fuel additive system for proper emissions control and DPF regeneration.
✔ Fuel additive injection may stop.
✔ DPF regeneration may fail.
✔ Emission levels may increase.
✔ Engine power may be limited.
✔ Prompt diagnosis is recommended.
Estimated Repair Cost
Repair costs depend on whether the problem involves wiring, connectors, power supply circuits, or the Fuel Additive Control Module itself.
| Repair | Estimated Cost (USD) |
|---|---|
| Professional Diagnosis | $80–150 |
| Repair CAN Bus Wiring | $100–350 |
| Connector Repair | $50–180 |
| Fuse or Relay Replacement | $20–80 |
| Module Programming | $100–300 |
| Replace Fuel Additive Control Module | $400–1,800+ |
Diagnostic Procedure
Diagnosing U0118 requires confirming that the Fuel Additive Control Module (FACM) has proper battery voltage, ignition power, ground, and uninterrupted High-Speed CAN Bus communication. Since most U0118 cases are caused by electrical faults rather than module failure, wiring and connector inspections should always be completed before replacing the control module.
↓ Read All Stored DTCs
↓ Save Freeze Frame Data
↓ Check Battery Voltage
↓ Inspect Fuses & Relays
↓ Verify Module Power Supply
↓ Verify Ground Circuit
↓ Measure CAN High Voltage
↓ Measure CAN Low Voltage
↓ Inspect Wiring & Connectors
↓ Repair Fault
↓ Clear Codes
↓ Road Test
Electrical Inspection
Electrical testing should begin at the Fuel Additive Control Module connector. Verify that power, ground, and CAN Bus circuits meet manufacturer specifications before condemning the module.
| Inspection Item | Normal Specification |
|---|---|
| Battery Voltage | 12.4–12.8 V |
| Charging Voltage | 13.5–14.8 V |
| Ground Resistance | Less than 0.2 Ω |
| CAN Network Resistance | Approximately 60 Ω |
| CAN High Voltage | ≈2.5–3.5 V |
| CAN Low Voltage | ≈1.5–2.5 V |
Live Data Analysis
Using a professional scan tool, verify that the Fuel Additive Control Module is communicating correctly and reporting live operational data to the Engine Control Module.
| Live Data Parameter | Normal | Fault Condition |
|---|---|---|
| Fuel Additive Module Status | Online | Offline |
| CAN Communication | Normal | Communication Error |
| Fuel Additive Level | Valid Reading | Unavailable |
| Additive Pump Command | Active When Required | No Response |
| Battery Voltage | Stable | Low Voltage |
Professional Diagnostic Tips
- Scan every control module before disconnecting the battery.
- Save Freeze Frame and network topology information.
- Inspect wiring near the fuel tank, additive reservoir, and chassis connectors.
- Load-test power and ground circuits instead of measuring voltage only.
- Measure CAN Bus resistance with the ignition OFF and battery disconnected.
- Perform a wiring wiggle test while monitoring Live Data.
- Inspect connectors for diesel fuel, DEF, moisture, or corrosion contamination.
- Check manufacturer Technical Service Bulletins (TSBs) before replacing the Fuel Additive Control Module.
Typical Wiring Diagram
The Fuel Additive Control Module (FACM) normally receives battery voltage, ignition voltage, and chassis ground while communicating with other vehicle modules through the High-Speed CAN Bus. The exact connector layout and wire colors vary by manufacturer.
Typical Fuel Additive Control Module Pinout
The following pinout represents a common High-Speed CAN configuration used on many vehicles. Always verify terminal identification using the manufacturer's wiring diagram before testing.
| Pin | Circuit | Expected Value |
|---|---|---|
| 1 | Battery Power (B+) | 12 V |
| 2 | Ignition Power | 12 V (Key ON) |
| 3 | Ground | Below 0.2 Ω |
| 4 | CAN High | ≈2.5–3.5 V |
| 5 | CAN Low | ≈1.5–2.5 V |
| 6 | Fuel Additive Pump Control | Manufacturer Specific |
| 7 | Fuel Additive Level Signal | Manufacturer Specific |
CAN Communication Signal Flow
Connector Inspection Checklist
- Inspect the connector for moisture, diesel fuel, DEF fluid, or additive contamination.
- Check for bent, loose, overheated, or corroded terminals.
- Verify terminal tension using the proper terminal inspection tool.
- Inspect the wiring harness near the fuel tank for abrasion or rodent damage.
- Look for melted insulation caused by exhaust heat or chassis contact.
- Perform a wiggle test while monitoring communication with a scan tool.
- Repair damaged terminals before replacing the Fuel Additive Control Module.
Recommended Diagnostic Equipment
| Tool | Purpose |
|---|---|
| Professional Scan Tool | Read communication faults and Live Data |
| Digital Multimeter | Voltage, resistance, and continuity testing |
| Dual-Channel Oscilloscope | Analyze CAN High and CAN Low waveforms |
| Back-Probe Test Leads | Measure circuits without damaging connectors |
Oscilloscope Waveform Analysis
A dual-channel automotive oscilloscope is the preferred tool for diagnosing U0118. It allows technicians to monitor High-Speed CAN Bus communication directly at the Fuel Additive Control Module (FACM) and determine whether the communication failure is caused by wiring, poor connections, electrical interference, or an internal module fault.
Connect Channel A to CAN High and Channel B to CAN Low at the Fuel Additive Control Module connector. Compare the captured waveform with the reference patterns below.
1. Normal High-Speed CAN Communication
CAN Low 2.5V ──╮────╮ ╭────╮────╮ 1.5V ──╯ ╰────╯ ╰────╯
Diagnosis: Normal CAN Bus communication. The Fuel Additive Control Module is transmitting and receiving network messages correctly.
2. CAN High Open Circuit
CAN Low 2.5V ─╮──╮──╮──╮──╮──╮──╮── 1.5V ─╯──╰──╯──╰──╯──╰──╯──
Diagnosis: CAN High wiring is open between the Fuel Additive Control Module and the CAN network.
3. CAN Low Open Circuit
CAN Low 2.5V ─────────────────────────
Diagnosis: CAN Low wiring is disconnected or has excessive resistance.
4. CAN Bus Short to Ground
CAN Low 0V ───────────────────────────
Diagnosis: One or both CAN circuits are shorted to ground. Inspect damaged insulation, crushed harnesses, and moisture intrusion.
5. CAN Bus Short to Battery Voltage
CAN Low 5V ───────────────────────────
Diagnosis: Battery voltage is present on the communication network. Check for harness damage, aftermarket wiring, or an internally shorted control module.
6. Intermittent Communication / Electrical Noise
CAN Low ╰╯╰╯────╰╯╰────╰╯╰
Diagnosis: Electrical interference or intermittent CAN communication caused by loose connectors, poor grounding, vibration, or partially broken wiring.
Professional Oscilloscope Tips
- Always compare CAN High and CAN Low simultaneously using a dual-channel oscilloscope.
- Use back-probe test leads to avoid terminal damage.
- Capture waveforms with the engine OFF, idling, and during a road test.
- Use trigger mode to detect intermittent communication dropouts.
- If one CAN circuit remains fixed while the other is active, inspect the inactive wire for an open circuit.
- Random voltage spikes usually indicate poor grounding or electromagnetic interference.
- Compare the repaired waveform with the normal High-Speed CAN reference before returning the vehicle to service.
Recommended Repairs
After identifying the root cause of U0118, repair the electrical or communication fault before replacing the Fuel Additive Control Module. Most U0118 cases are resolved by repairing wiring, connectors, or power supply circuits.
| Repair Procedure | Difficulty | Success Rate |
|---|---|---|
| Repair CAN High / CAN Low wiring | Medium | ★★★★★ |
| Repair connector corrosion | Easy | ★★★★★ |
| Repair module ground circuit | Easy | ★★★★☆ |
| Restore power supply | Medium | ★★★★☆ |
| Replace fuse or relay | Easy | ★★★★☆ |
| Update or reprogram FACM software | Advanced | ★★★☆☆ |
| Replace Fuel Additive Control Module | Advanced | ★★☆☆☆ |
Common Repair Mistakes
- Replacing the Fuel Additive Control Module before checking CAN Bus wiring.
- Ignoring low battery voltage during diagnosis.
- Failing to inspect fuse box terminals for corrosion.
- Overlooking poor chassis and engine ground connections.
- Clearing DTCs before recording Freeze Frame data.
- Ignoring additional communication (U-series) trouble codes.
- Using continuity tests only instead of voltage-drop testing.
- Installing a replacement module without required programming or calibration.
Manufacturer-Specific Notes
The Fuel Additive Control Module design varies significantly between manufacturers. Some vehicles integrate additive control into the Engine Control Module, while others use a dedicated CAN Bus module located near the fuel tank or additive reservoir.
| Manufacturer | Typical Configuration |
|---|---|
| Ford | PCM Fuel Additive Strategy |
| GM | Emission Control Network |
| Toyota | Integrated Engine ECU Control |
| Honda | PGM-FI Network |
| Volkswagen / Audi | J533 Gateway Communication |
| BMW | DDE/DME Additive Management |
| Mercedes-Benz | ME / CDI Engine Electronics |
| Peugeot / Citroën | Eolys Fuel Additive Module |
Vehicle Applications
The U0118 Diagnostic Trouble Code can appear on many OBD-II vehicles that use a dedicated Fuel Additive Control Module or similar emission-control controller. Although the code definition remains the same, module location, wiring, and system operation vary by manufacturer.
| Manufacturer | Typical System | Primary Inspection Area |
|---|---|---|
| Ford | Emission Additive Network | Power supply & HS-CAN wiring |
| Chevrolet / GMC | Diesel Emission Control | Ground circuits & communication |
| Toyota | Engine ECU Additive Strategy | CAN junction connectors |
| Honda | PGM-FI Communication | F-CAN network integrity |
| Volkswagen / Audi | Gateway Communication | J533 Gateway & CAN Bus |
| BMW | DDE Engine Management | Module power & CAN signals |
| Mercedes-Benz | CDI Emission Electronics | Communication network |
| Peugeot / Citroën | Eolys Fuel Additive System | Additive ECU & reservoir wiring |
Related Diagnostic Trouble Codes
Communication failures involving the Fuel Additive Control Module are often accompanied by other network-related Diagnostic Trouble Codes. Diagnose all stored communication codes before replacing any electronic control module.
- U0100 – Lost Communication With ECM/PCM "A"
- U0101 – Lost Communication With Transmission Control Module
- U0115 – Lost Communication With ECM/PCM "B"
- U0116 – Lost Communication With Engine Coolant Temperature Control Module
- U0117 – Lost Communication With Engine Coolant Temperature Sensor Module
- U0121 – Lost Communication With ABS Control Module
- CAN Bus Communication System
- Fuel Additive System Operation
Professional Technician Tips
- Scan every vehicle module before disconnecting the battery.
- Save Freeze Frame and network topology information.
- Inspect wiring near the fuel additive tank, chassis rails, and rear harness connectors.
- Perform voltage-drop testing on power and ground circuits.
- Use a dual-channel oscilloscope when intermittent CAN faults are suspected.
- Compare fuel additive level and module status using Live Data.
- Verify proper additive pump operation after repairs.
- Complete a full drive cycle and confirm that U0118 does not return.
Frequently Asked Questions (FAQ)
What does the U0118 code mean?
U0118 indicates that communication with the Fuel Additive Control Module (FACM) has been lost over the High-Speed CAN Bus network.
Can I continue driving with U0118?
In many vehicles, yes—but it is not recommended. The engine may continue to operate while the fuel additive system is disabled, potentially causing DPF regeneration problems, increased emissions, and reduced engine performance.
Is U0118 caused by a faulty fuel additive pump?
Not usually. U0118 is a communication fault rather than a pump failure. The most common causes include damaged CAN Bus wiring, poor electrical connections, low battery voltage, blown fuses, or an internal Fuel Additive Control Module fault.
Can a weak battery trigger U0118?
Yes. Low battery voltage or charging system problems can interrupt CAN Bus communication and trigger U-series Diagnostic Trouble Codes, including U0118.
Can corrosion cause U0118?
Yes. Corrosion inside connectors, moisture intrusion, road salt, diesel fuel contamination, or damaged wiring near the additive tank are common causes of intermittent communication failures.
Will clearing the code permanently fix the problem?
No. Clearing the code only erases the stored Diagnostic Trouble Code. If the communication fault still exists, U0118 will return after one or more drive cycles.
What should CAN Bus resistance measure?
With the ignition OFF and battery disconnected, resistance measured between CAN High and CAN Low should be approximately 60 Ohms.
Is an oscilloscope necessary?
While many problems can be found using a professional scan tool and multimeter, a dual-channel automotive oscilloscope is the best tool for diagnosing intermittent CAN Bus communication faults.
Does a replacement Fuel Additive Control Module require programming?
Yes. Many manufacturers require software programming, configuration, or security synchronization after replacing the Fuel Additive Control Module.
How much does it cost to repair U0118?
Repair costs typically range from $50 for connector repairs to more than $1,800 if the Fuel Additive Control Module must be replaced and programmed.
Conclusion
The U0118 Code – Lost Communication With Fuel Additive Control Module is a High-Speed CAN Bus communication fault that can affect fuel additive delivery, diesel particulate filter regeneration, emissions performance, and overall engine management. Proper diagnosis should always begin with battery voltage verification, power and ground testing, CAN Bus inspection, connector examination, Live Data analysis, and oscilloscope waveform testing before replacing the Fuel Additive Control Module. Following a structured diagnostic process minimizes unnecessary repairs and restores reliable network communication.
Key Takeaways
- U0118 is a CAN Bus communication fault—not a fuel additive pump performance code.
- Most repairs involve damaged wiring, poor connectors, blown fuses, or faulty ground circuits.
- Always inspect High-Speed CAN Bus integrity before replacing the Fuel Additive Control Module.
- Live Data and oscilloscope analysis provide the most accurate diagnosis.
- Record Freeze Frame information before clearing any Diagnostic Trouble Codes.
- Verify proper fuel additive operation and confirm that U0118 does not return after repairs.
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