Espar / Eberspacher Airtronic D2 / D4 (classic generation) error code 011
Undervoltage cut-off - supply below the minimum for 20+ seconds without interruption. The cited Espar diagnostic manual's 12 V figure is 10.5 V; it publishes no 24 V undervoltage figure - use the 24 V unit's own spec rather than assuming one.
What to check, and in what order, is in the app. The flow Diesel Forced-Air Heater — entry diagnostic (Espar / Webasto / Autoterm / Chinese) walks this code step by step with the pass/fail measurements, wiring schematics and procedures that go with it, and it works offline in the bay.
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