Code Definition

P1901 — Radiator fan run-on relay shorted to positive

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

About P1901

P1901 is a manufacturer-specific powertrain diagnostic trouble code recorded for Audi 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

DTC P1901 sets when the engine control module (ECM) detects that the radiator fan run on relay circuit is shorted to positive, so the relay is seeing constant power or is stuck energised. The run on relay lets the cooling fan keep operating for a period after the engine is switched off to draw heat out of the engine bay. When the circuit is shorted to positive, the fan can run far longer than intended or run continuously, which flattens the battery, adds noise, and often points to a stuck relay or a wiring fault feeding the control circuit. Symptoms include the fan running with the ignition of...

Join TaT to view the complete code information and diagnostic details.

Quick Facts