Fuel Filter Restriction High or Rail Pressure Low
What does ATLAS-COPCO-E031 mean?
The ATLAS-COPCO-E031 (Atlas Copco Xc4002 / Xc2003 / Xc4004) diesel fault code means: Fuel Filter Restriction High or Rail Pressure Low. This is a moderate severity code.
Common Symptoms
- Xc4002 / Xc2003 / Xc4004 controller LCD displays E031 on the side panel
- Engine runs rough, surges, or stumbles under load
- Unit shuts down or derate kicks in during peak air demand
- Compressor output pressure drops below setpoint even with engine running
- Engine may crank and start but struggles to hold RPM at load
- Yellow or red alarm indicator is lit on the control panel
- Restart after shutdown is sluggish and engine takes longer to build pressure
Probable Causes (Ranked by Likelihood)
- Primary fuel filter element plugged with debris or water contamination Very Likely
- Secondary fuel filter element at or past service interval Very Likely
- Water-in-fuel separator bowl full, blocking flow Likely
- Fuel restriction switch or differential pressure sensor failed or stuck closed Possible
- Fuel tank pickup tube partially blocked by sediment or algae growth Possible
- Fuel supply line kinked, collapsed, or pinched during towing Less Likely
- Lift pump weak or failing, unable to supply adequate feed pressure to filters Less Likely
Step-by-Step Diagnostic Procedure
Check the controller LCD on the side panel first. Confirm E031 is the active fault and note whether any secondary codes appear alongside it. Press the STOP button to silence the alarm before beginning inspection.
Inspect the primary fuel filter bowl and water separator. If the bowl is cloudy, milky, or has visible water or sediment in the bottom, drain it before doing anything else. Many E031 trips on rental units are caused by nothing more than a full water separator bowl.
Check the primary filter element condition. Hold it up to daylight or a work light. If the element is dark brown or black, or if the unit has been in service more than 500 hours since last filter change, replace it now. Atlas Copco spec is typically 500-hour or annual intervals depending on the model.
Replace the secondary (fine) fuel filter element at the same time as the primary. On Kubota-powered XAS 185 units the secondary is on the engine side of the fuel circuit. On Deutz-powered XAS 375 units check both the engine-mounted filter and the compressor-side pre-filter. Do not skip the secondary filter even if it looks clean.
After replacing both filters, manually prime the fuel system using the hand primer pump if equipped (most Kubota and Deutz installations have one). Pump until resistance builds, then crank the engine. On CAT C7 units in the XAS 800 you may need to use DiagPro service software via the J1939 / CAN data port to command a fuel prime cycle if air lock is suspected.
If E031 returns within minutes of a fresh filter set, check the restriction switch or differential pressure sensor. Locate the switch on the primary filter housing. With the engine OFF and key in the RUN position, unplug the sensor connector and use a multimeter set to DC resistance. The switch should read open circuit (no continuity) when filters are clean. If it reads continuity with new filters installed, the switch is faulty. Replace the restriction switch and retest.
Inspect the fuel supply line from the tank to the first filter housing. Look for kinks, collapsed sections, or zip-tie pinch points that may have occurred during towing. Flex the line by hand along its full run and confirm it springs back without restriction.
If all filters are new, the separator is drained, the restriction switch tests good, and E031 still sets, suspect the lift pump. Attach a fuel pressure gauge to the inlet side of the primary filter. Crank the engine and check feed pressure against spec. Kubota V2403 spec is typically 0.3 to 0.5 bar at the filter inlet. Low or zero pressure with a known-good supply line points to a lift pump replacement. This step requires a gauge fitting and is the boundary where you should call an Atlas Copco service tech if you are not set up for it.
Frequently Asked Questions
What does Atlas Copco code E031 mean?
E031 means the controller has detected high restriction in the fuel circuit, most commonly because one or both fuel filter elements are plugged, the water separator bowl is full, or rail pressure cannot be maintained under load. The Xc4002 / Xc2003 / Xc4004 controller monitors a differential pressure switch across the primary filter. When that switch trips, E031 sets.
Can the compressor still run with E031 active?
Usually yes, in a limited sense. The unit will often stay running at low load but may derate or shut down when air demand spikes. Do not rely on it for sustained production work. Starving the injection system of fuel causes premature wear on injectors and the lift pump. Fix the filter restriction before putting the machine back on a job.
How much does it cost to fix E031?
If it is just clogged filters, parts cost $25 to $80 depending on the engine. You can do it yourself with basic hand tools in about 30 minutes. If the restriction switch has failed or the lift pump is weak, a shop will charge $150 to $600 depending on what needs replacing and how long the machine has been starved.
The filters look fairly new. Why is E031 still showing?
A few possibilities. First, drain the water separator bowl even if the filters are new. Water contamination can trip E031 independently of filter condition. Second, the restriction switch itself may be stuck or failed. Third, on rental units that sit between jobs, algae or tank sediment can plug a new filter quickly if the tank was not cleaned. If the code clears after draining the separator bowl, you found your culprit.