Dirty or carbon-fouled idle air control solenoid valve, restricting movement and skewing the feedback signal; Damaged or corroded wiring or connector terminals on the IAC solenoid circuit, particularly the signal 2 wire; Open or shorted IAC solenoid winding on the signal 2 circuit; Failed engine control module (ECM) driver for the IAC circuit, though this is less common; Intake air leaks downstream of the throttle body that alter idle air flow and confuse the IAC feedback; Poor engine ground or reference voltage supply shared with the IAC circuit

DTC codes / Subaru codes / P1512

P1512 · SubaruIdle Air Control Solenoid Signal 2 Circuit Low Input

Q: What does code P1512 mean?

Idle Air Control Solenoid Signal 2 Circuit Low Input. P1512 on a Subaru means the engine control module (ECM) has detected a low input signal on the second circuit of the idle air control (IAC) solenoid, which is the valve that meters air around the closed throttle plate to keep idle steady. The ECM expects a specific voltage or current feedback on that circuit and saw it fall below the acceptable threshold, so it flags the circuit as faulty.

P1512 on a Subaru means the engine control module (ECM) has detected a low input signal on the second circuit of the idle air control (IAC) solenoid, which is the valve that meters air around the closed throttle plate to keep idle steady. The ECM expects a specific voltage or current feedback on that circuit and saw it fall below the acceptable threshold, so it flags the circuit as faulty.

SystemPowertrain

Code typeSubaru specific

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

Check engine light illuminated, often with no other noticeable symptoms
Rough or stumbling idle, especially when cold or when electrical loads are switched on
Idle speed that hangs too high or drops too low and fluctuates
Engine stalling when coming to a stop or when the throttle is released
Occasional surging during idle in gear on automatic transmission models

Common causes, most likely first

Dirty or carbon-fouled idle air control solenoid valve, restricting movement and skewing the feedback signal
Damaged or corroded wiring or connector terminals on the IAC solenoid circuit, particularly the signal 2 wire
Open or shorted IAC solenoid winding on the signal 2 circuit
Failed engine control module (ECM) driver for the IAC circuit, though this is less common
Intake air leaks downstream of the throttle body that alter idle air flow and confuse the IAC feedback
Poor engine ground or reference voltage supply shared with the IAC circuit

How to diagnose and fix it

Scan all modules for stored and pending codes, then clear and road-test to confirm P1512 returns
Inspect the IAC solenoid connector and harness for corrosion, chafing, or pushed-out terminals, and repair as needed
Measure resistance across the IAC solenoid windings and compare to the manufacturer's specification
Back-probe the signal 2 circuit at the ECM and check voltage or duty cycle while commanding idle air control with a scan tool
Remove and clean the IAC valve and throttle body passages, then reinstall and recheck idle operation
Perform a smoke test or propane enrichment test to rule out unmetered intake air leaks
If the circuit and valve test good, substitute a known-good IAC valve or ECM to isolate the fault before replacement

What a low IAC signal really means

A low signal on circuit 2 does not automatically condemn the IAC valve; a corroded ground or a chafed wire in the harness often produces the same code and is far cheaper to fix.
Subaru IAC valves are sensitive to carbon buildup, and a valve that is merely sticky can set P1512 without ever failing a resistance test, so cleaning is a valid first step before replacement.
Unmetered air from a cracked intake boot or a leaking intake manifold gasket can drive the IAC duty cycle outside its expected range and trigger this code even though the solenoid itself is healthy.
Technicians sometimes replace the IAC valve only to find the ECM driver is faulty, so always verify the control signal at the ECM before condemning the valve.
On some Subaru models the IAC circuit shares a ground path with other sensors, so a single bad ground can set P1512 alongside unrelated sensor codes.

Can I keep driving with P1512?

You can usually drive the car to a workshop, but expect an unstable idle and possible stalling when you lift off the throttle, so avoid heavy traffic and keep your foot ready on the brake. Do not ignore the code for long, because repeated stalling can affect brake assist and power steering on older Subaru models.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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