Code Definition

P1905 — Charge air cooler pump relay shorted to positive

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

About P1905

P1905 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 P1905 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.

P1905 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 P1905 sets when the engine control module (ECM) detects a short to positive in the charge air cooler pump relay circuit. On turbocharged and supercharged Audi engines with a liquid cooled intercooler, this electric pump circulates coolant through the charge air cooler to pull heat out of the compressed intake air, and the ECM switches it through a relay. When the relay control circuit is shorted to positive, the ECM can no longer control the pump, so it may run continuously or erratically. This can drain the battery while the vehicle is parked, run the pump unnecessarily, and reduce the ab...

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