U0118 Lost Communication with Fuel Additive Control Module

OBD-II DTC Datasheet

Lost Communication With Fuel Additive Control Module

What does this mean?

This is a generic communication system diagnostic trouble code that applies to most makes and models of vehicles.

This code means that the fuel additive control module (FACM) and other control modules on the vehicle are not communicating with each other. The circuitry most commonly used for communication is known as Controller Area Bus communication, or simply the CAN bus.

Without this CAN bus, control modules cannot communicate and your scan tool may not receive information from the vehicle, depending on which circuit is involved.

The FACM receives input data from various sensors, some of which are directly connected to it, and some of which are transmitted via a bus communication system. These inputs allow the module to provide the necessary inputs to the PCM to control the amount of fuel supplied to the engine in all operating modes.

Troubleshooting steps may vary depending on the manufacturer, the type of communication system, the number of wires, and the colors of the wires in the communication system.

Severity and symptoms

The severity in this case depends on the system. Because this powertrain control system provides fuel information to the powertrain control module (PCM), safety is a concern when diagnosing these systems. In addition, safety is important when servicing these systems. ALWAYS refer to the service information before disassembling / diagnosing these systems. Symptoms may include:

Symptoms of a U0118 engine code may include:

Fault indicator light is on
Engine cranks, starts, but performs poorly, including: misfiring, uneven operation, poor performance.

reasons

Usually the reason for installing this code is:

Open in CAN + bus circuit
Open in the CAN bus - electrical circuit
Short circuit to power in any CAN bus circuit
Short to ground in any CAN bus circuit
Loss of power or ground on the FACM - the most common
Rarely - the control module is faulty

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

First, look for other DTCs. If any of these are bus communication or battery / ignition related, diagnose them first. Misdiagnosis is known to occur if you diagnose the U0118 code before any of the major codes are thoroughly diagnosed and rejected.

If your scan tool can access trouble codes and the only code you are pulling from other modules is U0118, try accessing the fuel additive control module. If you can access the codes from the FACM, then code U0118 is either intermittent or a memory code. If the codes for the FACM module cannot be accessed, then code U0118 set by other modules is active and the problem already exists.

The most common failure is a loss of power or ground to the FACM.

Check all fuses supplying the FACM on this vehicle. Check all grounds for FACM. Locate grounding attachment points on the vehicle and make sure these connections are clean and secure. If necessary, remove them, take a small wire bristle brush and baking soda / water solution and clean each one, both the connector and the place where it connects.

If any repairs have been made, clear the DTCs from memory and see if U0118 returns or you can contact the FACM. If no code is returned or communication is restored, the problem is most likely a fuse / connection issue.

If the code returns, look for the CAN bus connections on your specific vehicle, especially the FACM connector. Disconnect the negative battery cable before disconnecting the connector on the FACM. Once detected, visually inspect the connectors and wiring. Look for scratches, scuffs, exposed wires, burn marks, or molten plastic. Disconnect the connectors and carefully inspect the terminals (metal parts) inside the connectors. See if they look burnt or have a green tint indicating corrosion. If you need to clean the terminals, use an electrical contact cleaner and a plastic bristle brush. Allow to dry and apply electrical grease where the terminals touch.

Perform these few voltage checks before connecting the connectors back to the FACM. You will need access to a digital volt/ohmmeter (DVOM). Make sure you have power and ground on the FACM. Access the wiring diagram and determine where the main power and ground supplies enter the FACM. Reconnect the battery before continuing with the FACM still disabled. Connect the red lead of your voltmeter to each B+ (battery voltage) power supply plugged into the FACM connector, and the black lead of your voltmeter to a good ground (if unsure, battery negative always works). You see the battery voltage reading. Make sure you have a good reason. Connect the red lead of the voltmeter to the battery positive (B+) and the black lead to each ground circuit. Once again, you should see the battery voltage every time you connect. If not, repair the power or ground circuit.

Then check the two communication circuits. Locate CAN C+ (or HSCAN+) and CAN C- (or HSCAN - circuit). With the black wire of the voltmeter connected to a good ground, connect the red wire to CAN C+. With the key on and engine off, you should see about 2.6 volts with little fluctuation. Then connect the red wire of the voltmeter to the CAN C- circuit. You should see about 2.4 volts with little fluctuation. Other manufacturers show CAN C- at about 5V and an oscillating key with the engine off. Check your manufacturer's specifications.

If all tests pass and communication is still not possible, or you were unable to reset DTC U0118, the only thing to do is to seek help from a trained automotive diagnostician as this will indicate a faulty FACM. Most of these FACMs must be programmed or calibrated for the vehicle in order to be properly installed.

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