P0505 on Cadillac
Idle Air Control System Malfunction
P0505 on Cadillac vehicles indicates idle air control system malfunction. Au7o has documented this code across 1 Cadillac model — most commonly on CT4. P0505 indicates a malfunction in the idle air control (IAC) system, which manages how much air bypasses the throttle plate to keep the engine idling smoothly at the correct RPM. On older systems this is a dedicated IAC valve/motor; the computer uses it to raise idle for cold starts, A/C load, or accessory load. When the system can't maintain the target idle, you may get a high or low idle, surging, rough idle, or stalling — especially at stops or when cold. The cause is usually a dirty or failed IAC valve, but vacuum leaks and electrical faults are common too.
Common Causes of P0505
- •Dirty or carbon-clogged idle air control valve
- •Failed IAC valve motor or stuck pintle
- •Vacuum leak in the intake system
- •Dirty throttle body or sticking throttle plate
- •Wiring or connector fault in the IAC circuit
- •Faulty PCV system causing unmetered air
- •PCM/ECM control fault
P0505 on Cadillac by Model
Cadillac CT4(1 issue)
- Intermittent Stalling and Rough Idle in Stop-and-Go Traffic2022-2024
Some CT4-V Blackwing models with the 10-speed automatic transmission experience intermittent stalling and rough idle in stop-and-go traffic conditions. The engine may die at standstill and require restart. Reports indicate this occurring within the first 1,000 miles on new vehicles, suggesting a calibration issue rather than mechanical failure. GM has released preliminary engineering bulletins (PIE0744) for the 10-speed automatic in Blackwing models.
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View P0505 across all makes →Frequently Asked Questions
What does P0505 mean on Cadillac?▼
P0505 stands for "Idle Air Control System Malfunction." P0505 indicates a malfunction in the idle air control (IAC) system, which manages how much air bypasses the throttle plate to keep the engine idling smoothly at the correct RPM. On older systems this is a dedicated IAC valve/motor; the computer uses it to raise idle for cold starts, A/C load, or accessory load. When the system can't maintain the target idle, you may get a high or low idle, surging, rough idle, or stalling — especially at stops or when cold. The cause is usually a dirty or failed IAC valve, but vacuum leaks and electrical faults are common too. On Cadillac specifically, this code is documented across 1 model.
What causes P0505 on Cadillac vehicles?▼
Common causes on Cadillac: Dirty or carbon-clogged idle air control valve, Failed IAC valve motor or stuck pintle, Vacuum leak in the intake system, Dirty throttle body or sticking throttle plate, Wiring or connector fault in the IAC circuit. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0505 on a Cadillac?▼
Repair costs vary widely depending on the root cause and specific Cadillac model.
Which Cadillac models have P0505 documented?▼
Au7o has documented P0505 on 1 Cadillac model: CT4.