Ako E4 Error Code

What does Ako E4 mean?

E4 indicates a fault on Probe 4 on multi-probe AKO controllers (such as the AKO-16526 series). The fault is an open circuit, a crossed/short circuit, or a temperature value outside the valid sensor limits. On the AKO-16526, up to six sensor inputs are supported, and E4 through E6 correspond to probes 4 through 6. The alarm relay and audible alarm activate when E4 is present.

Symptoms

• E4 appears on the display alternating with the temperature reading.
• Alarm relay and audible alarm activate.
• Any relay output or control function dependent on Probe 4 is suspended.
• The controller may fall back to alternative control logic if Probe 4 was used as a secondary or safety sensor.
• Probe 4-based temperature readings are unavailable.

Common causes

• Open circuit in the Probe 4 cable or at the terminal connection (most common).
• Short or crossed wiring at the Probe 4 terminal block.
• Probe 4 temperature exceeds valid NTC/PTC sensor limits due to installation in an extreme environment.
• Moisture ingress at the Probe 4 tip causing resistance drift.
• Incorrect probe type installed at Probe 4 position relative to controller parameter settings.

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Diagnostic steps

1. Identify Probe 4 location and function

   Determine where Probe 4 is installed (discharge line, second evaporator, product zone, etc.) and which outputs or alarms depend on it. This determines the operational impact while repairs are underway.

2. Power off and inspect the Probe 4 cable

   De-energize the controller. Inspect the full cable run for Probe 4 for damage, chafing, or water ingress. Check the probe tip for corrosion.

3. Check the Probe 4 terminal connections

   Re-seat the Probe 4 connector at the controller terminal block. Tighten any loose terminals and clean corroded contacts with electrical contact cleaner.

4. Measure Probe 4 resistance

   Disconnect Probe 4 and measure resistance at the tip with a multimeter. Compare to the AKO NTC/PTC resistance–temperature table. An open circuit or out-of-range reading confirms probe failure.

5. Replace the faulty probe

   Install an AKO-approved replacement probe at the Probe 4 position. Route the cable separately from power wiring. Restore power and confirm E4 clears.

When to call a professional

Call a licensed refrigeration technician if Probe 4 is monitoring a safety-critical parameter (discharge temperature, motor winding temperature, or refrigerant leak sensor interface) and that measurement has been unavailable during the fault period. If E4 appears alongside other active alarms, a technician should assess the system's overall condition before returning it to service.