DTC codes / Volkswagen codes / P1616
P1616 on Volkswagen vehicles means the engine control module (ECM) has detected a short to battery positive voltage in the glow plug heater indicator circuit, which is the wire that feeds the glow plug warning lamp in the instrument cluster. The ECM expects this circuit to pull low when the glow plugs are active, but it sees continuous battery voltage, indicating a short to power rather than a faulty glow plug.
Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.
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