Air Filter Restriction Warning Detected

Common Symptoms

• Controller LCD on the side panel displays E040 and may show a wrench or alarm icon
• Yellow or amber warning lamp lights up on the control panel
• Engine exhaust turns black or dark gray, especially under load
• Air compressor output pressure drops and the machine struggles to keep up with demand
• Engine RPM may hunt or fluctuate as the governor fights restricted airflow
• Engine runs hotter than normal and the temperature gauge climbs toward the warning zone
• Machine continues to run but feel sluggish, taking longer to build pressure in the receiver tank

Probable Causes (Ranked by Likelihood)

• Air filter element is clogged with dust, debris, or construction site particulates Very Likely
• Air filter restriction indicator or differential pressure switch has failed or is stuck closed Likely
• Air filter housing or pre-cleaner bowl packed with debris preventing airflow Likely
• Collapsed or kinked intake hose between the air filter housing and the engine intake Possible
• Wiring fault or open circuit on the restriction switch signal wire back to the controller Possible
• Wrong replacement filter element installed with an incorrect size or lower flow rating Less Likely
• Moisture or water ingestion causing filter media to swell and block airflow Less Likely

Step-by-Step Diagnostic Procedure

1. Start at the air filter housing. Locate the restriction indicator or differential pressure switch mounted on the housing or intake tube. Check if the red pop-up indicator (if equipped) is extended. That confirms restriction before you even pull the element.

2. Remove and visually inspect the air filter element. Hold it up to a light source. If you cannot see light through the pleats, the element is done. Do not try to blow it out with compressed air on Kubota or Deutz engines. Atlas Copco recommends element replacement, not cleaning.

3. Inspect the pre-cleaner bowl or dust ejector at the top of the housing. Empty any accumulated dirt. A packed pre-cleaner can choke the engine just as badly as a dirty element.

4. Check the entire intake tract from the air filter outlet to the engine intake manifold. Look for collapsed hoses, loose clamps, or cracks. A collapsed hose will trigger E040 with a clean filter inside.

5. With the new or known-good filter installed and the engine OFF, locate the restriction switch connector. Use a multimeter set to continuity or resistance. With airflow unrestricted, the switch should be open (no continuity). If it reads closed with a clean filter, the switch itself has failed. Replacement switches are typically available from Atlas Copco parts at a reasonable cost.

6. Inspect the wiring harness from the restriction switch back to the Xc4002 / Xc2003 / Xc4004 controller. Look for chafed insulation, corroded pins at the connector, or a wire pulled out of the terminal. A short to ground on this wire can keep E040 active even with a new filter and good switch.

7. After replacing the filter element and clearing any debris, start the engine and let it run under load for 5 minutes. If E040 clears on its own or after a soft reset on the controller, the root cause was the dirty filter. If E040 returns immediately with a clean filter and verified intake tract, escalate to a service tech with DiagPro service software to check switch calibration thresholds and controller input status via the J1939 / CAN data port.

8. Log the service interval. On jobsite machines running in dirt, dust, or high-debris environments, filter service intervals should be cut to half the standard interval shown in the Atlas Copco maintenance schedule.

Frequently Asked Questions