Emergency Stop Loop Open or E-Stop Activated

Common Symptoms

• Controller LCD shows E050 and the compressor shuts down immediately or refuses to start
• RED fault lamp on the Xc4002 / Xc2003 / Xc4004 panel is lit solid
• Pressing the RUN button does nothing and the unit stays in STOP state
• Compressor does not build pressure and the engine cranks but immediately cuts fuel, or does not crank at all
• Remote E-stop mushroom button indicator light is illuminated at the control box or remote panel
• Unit was running normally, then shut down without any high-temp or high-pressure warning
• All other system parameters appear normal on the controller display but the machine will not restart

Probable Causes (Ranked by Likelihood)

• Remote or local emergency stop mushroom button is still pressed in or latched Very Likely
• E-stop safety loop wiring has an open circuit due to a broken wire, loose terminal, or damaged connector Likely
• Remote E-stop button on a secondary control panel (jobsite wiring) was tripped and not reset Likely
• Corroded or dirty E-stop button contacts preventing continuity even when the button appears released Possible
• Controller Xc4002 / Xc2003 / Xc4004 internal input channel fault or damaged safety relay on the E-stop circuit board Less Likely
• Aftermarket remote start or shutdown device wired into the E-stop loop has failed open Less Likely

Step-by-Step Diagnostic Procedure

1. Start at the panel. Check every E-stop mushroom button you can see, including the one on the Xc4002 / Xc2003 / Xc4004 side panel and any remote button at the hose reel or customer-supplied panel. Twist and pull each button clockwise to release the latch. A button that is still pressed in is the most common cause.

2. After releasing all E-stop buttons, press STOP on the controller to clear the latched fault, then attempt to restart by pressing RUN. The Xc4002 / Xc2003 / Xc4004 will not clear E050 automatically. You must manually reset through STOP before RUN.

3. If the code returns immediately after reset, trace the E-stop loop wiring. On most XAS series units, the E-stop circuit is a normally-closed (NC) two-wire loop from the controller terminal block out to each E-stop button and back. Find the terminal block inside the control cabinet, usually labeled EST or ESTOP. With the machine in STOP state and ignition off, use a multimeter set to continuity or resistance. You should read near 0 ohms across the loop terminals. An open reading (OL) confirms a broken wire or open contact.

4. Disconnect the E-stop loop at the controller terminal block and use a short jumper wire to bridge the two terminals directly. If E050 clears and the unit starts normally with the jumper in place, the fault is in the external wiring or one of the buttons, not the controller. Work outward from the controller, disconnecting and re-jumering each button in turn until you find the open segment.

5. Inspect all E-stop button connectors and wiring for visible damage. On towable units like the XAS 185 and XAS 375, the cable from the main panel to the remote button often runs along the frame and is vulnerable to pinching, abrasion, or tow-related damage. Look for cut insulation, crushed conduit, or corroded Deutsch connectors.

6. If all wiring and buttons test good (continuity reads 0 ohms through the entire loop) but E050 still appears, check the E-stop input voltage at the controller terminal. The Xc4002 / Xc2003 / Xc4004 expects a specific signal level on that input, typically 24V DC when the loop is closed. Measure DC voltage between the input terminal and ground with a multimeter. If voltage is absent even with a known-good closed loop, the controller input channel or safety relay may be failed and you will need DiagPro service software or Atlas Copco dealer support to confirm.

7. If a customer or rental customer has added any remote shutdown device, wireless SCADA receiver, or telematics box wired into the E-stop loop, disconnect it temporarily. These third-party devices can fail open and hold the E-stop loop open indefinitely. Reconnect the loop directly and test.

8. If none of the above steps resolve the fault, connect DiagPro via the J1939 / CAN data port and review the fault log for any secondary codes logged alongside E050. A concurrent sensor fault or controller hardware fault logged at the same timestamp can point to a different root cause than a simple E-stop button issue.

Frequently Asked Questions