U0108: Lost Communication With Alternative Fuel Control Module
The ECU has lost CAN communication with the alternative fuel control module (CNG/LPG/H2 systems). Either the module is not responding or the bus path is broken.
What U0108 means
U0108 is a generic OBD-II network code in the lost communication group. In plain English: a control module stopped receiving messages from the Alternative Fuel Control Module on the vehicle’s data network.
- Check engine light
- Usually on
- Emissions-related
- Yes — can fail inspection
- Limp mode possible
- Not typical
- Drive cycle to clear
- Required
Get it fixed
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Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
- 01Module unpowered or fuse blownMost likely
- 02CAN wiring to module brokenPossible
- 03Gateway module routing CAN messages incorrectlyLess likely
Can I drive with U0108?
Usually yes, for a short time.
The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
Why we rate it moderate
- Turns on the check engine light
- Emissions-related: will usually fail an OBD inspection
- Needs a drive cycle to confirm a repair
Severity is our rule-based rating from the code’s flags in OBDex and the system it affects, not an inspection of your car. If the check engine light is flashing, or you notice overheating, low oil pressure, or brake or steering problems, stop driving and get help.
How to diagnose U0108
- 1
Confirm the code and save freeze-frame data
Read the codes with an OBD-II scan tool and note every code, not just U0108. Save the freeze-frame data (speed, load, temperature when the fault set) before clearing anything; it tells you when the fault happens.
- 2
Fix other faults first
If other codes are stored, start with power-supply, sensor-circuit and communication codes. They can cause this code as a side effect.
- 3
Check module power, ground and the data bus
Confirm the module named in the code has battery voltage, ignition feed and a good ground. With the battery disconnected, a healthy CAN bus usually measures about 60 ohms between CAN-High and CAN-Low at the OBD port. Inspect connectors for corrosion and pushed-out pins.
- 4
Test the likely causes in order
Start with the most likely cause and work down: Module unpowered or fuse blown; CAN wiring to module broken; gateway module routing CAN messages incorrectly. Test before replacing parts.
- 5
Check for recalls and service bulletins
Look up recalls for your exact vehicle with its VIN, and ask a dealer about technical service bulletins (TSBs). Manufacturers sometimes issue software updates or extended warranties for known faults.
- 6
Clear the code and verify the repair
After the repair, clear the code and complete a full drive cycle (cold start, idle, steady highway cruise, deceleration). The code is fixed when the related readiness monitor completes without it returning.
U0108 repair cost estimate
Estimate, not a quote. Labor times are typical ranges for this code from OBDex, and $125/hr is an assumed rate. Shop rates and labor times vary by vehicle and region. Diagnosis time may be billed separately.
- DIY difficulty
- Moderate
- Good DIY job?
- Yes, with a scan tool
Needs a scan tool and some experience with testing.
Parts and systems involved
- Alt fuel module
- CAN bus
U0108 FAQ
What does U0108 mean?
U0108 means “Lost Communication With Alternative Fuel Control Module”. The ECU has lost CAN communication with the alternative fuel control module (CNG/LPG/H2 systems). Either the module is not responding or the bus path is broken.
Is U0108 serious? Can I keep driving?
We rate U0108 as moderate severity. Usually yes, for a short time. The car will often drive normally, but get it diagnosed soon. Left alone it can raise fuel use and emissions and will fail an OBD inspection. If you notice rough running, warning lights flashing, overheating or a burning smell, stop driving.
What causes U0108?
The most common causes, from most to least likely: Module unpowered or fuse blown; CAN wiring to module broken; Gateway module routing CAN messages incorrectly. Test before replacing parts, because several causes can set the same code.
How much does it cost to fix U0108?
Typical labor is about $65–$625 at an assumed $125/hour shop rate, plus parts. That is an estimate, not a quote: labor times and rates vary by vehicle and region, and diagnosis may be billed separately.
Can I fix U0108 myself?
DIY difficulty is moderate. Many owners can handle it with a scan tool, a multimeter and basic hand tools. Always confirm the cause before buying parts.
Will U0108 clear itself?
Once the fault is fixed, the check engine light usually goes off by itself after the system passes its self-test over several drive cycles. Clearing the code with a scan tool resets readiness monitors, so an inspection station may turn you away until a full drive cycle is completed.