Code Definition

P1901 — Radiator fan run-on relay shorted to positive

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Volkswagen

About P1901

P1901 is a manufacturer-specific powertrain diagnostic trouble code recorded for Volkswagen vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1901 is stored, the module has detected a short-circuit (voltage pulled to ground or to supply) in the monitored circuit.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1901 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

This fault code is set when the engine control module (ECM) detects that the radiator fan run-on relay is continuously powered due to a short-to-positive condition. The run-on relay allows the fan to continue operating after the engine is turned off to aid cooling. A shorted relay or wiring issue can cause the fan to run excessively, drain the battery, or lead to improper cooling system operation.

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