P0505: the idle air control system has a fault
The idle air control system lets the engine control unit hold the engine at a steady idle speed without your foot on the accelerator, by controlling a small amount of extra air, or on many newer engines by moving the electronic throttle itself. This code means that system isn't behaving the way the computer expects. It doesn't say whether the fault is in the valve or motor itself, its circuit, or somewhere else in the system, only that idle control isn't working as it should.
You might notice
- The engine warning light comes on
- The engine may idle too high, too low, or hunt up and down at idle
- idle air control system
- — the system that holds the engine at a steady idle speed without your foot on the accelerator
What the code itself says
P0505 is a powertrain (engine, gearbox and drive system) code, and the 0 after the letter means it is a generic code with a standard meaning.
Grouped here as: Engine running, fuelling and misfires — Air metering, fuelling, ignition, misfire, idle, boost, knock, oxygen sensors and the catalyst, all working together in the running engine. That grouping is ours, to help explain the code. The code's official family is the letter at the start.
This page is generic. Your car isn't.
A code on its own only tells you what the sensor saw, not what's actually wrong — and that changes next to your other codes. Read this one together with the rest of your scan and we'll work out what's really going on.
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