What does code P1518 mean?

Q: What does code P1518 mean?

Main Relay Circuit Short To B+. P1518 on Volkswagen vehicles means the engine control module (ECM) has detected a short to battery positive voltage in the main relay circuit, which supplies power to the engine management system. The ECM monitors the relay control wire and sees voltage present when it should be at ground or zero, indicating a wiring fault rather than a failed relay.

DTC codes / Volkswagen codes / P1518

P1518 · VolkswagenMain Relay Circuit Short To B+

P1518 on Volkswagen vehicles means the engine control module (ECM) has detected a short to battery positive voltage in the main relay circuit, which supplies power to the engine management system. The ECM monitors the relay control wire and sees voltage present when it should be at ground or zero, indicating a wiring fault rather than a failed relay.

SystemPowertrain

Code typeVolkswagen specific

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.