Corroded or loose electrical connector at the starter switch or ignition switch.; Damaged or chafed wiring in the starter switch circuit, often near the steering column or firewall.; Faulty ignition switch internal contacts causing high resistance.; Blown fuse or faulty fuse box connection in the starter circuit.; Poor ground connection for the starter or engine block.; Failed neutral safety switch or clutch pedal position sensor (on automatic or manual transmissions respectively).

DTC codes / Subaru codes / P1518

P1518 · SubaruStarter Switch Circuit Low Input

Q: What does code P1518 mean?

Starter Switch Circuit Low Input. P1518 on a Subaru indicates that the engine control module (ECM) has detected a low input voltage on the starter switch circuit, which is the signal wire that tells the ECM the key is in the start position. The ECM expects to see battery voltage on this circuit when cranking, and a low voltage indicates an open circuit, high resistance, or a faulty switch.

P1518 on a Subaru indicates that the engine control module (ECM) has detected a low input voltage on the starter switch circuit, which is the signal wire that tells the ECM the key is in the start position. The ECM expects to see battery voltage on this circuit when cranking, and a low voltage indicates an open circuit, high resistance, or a faulty switch.

SystemPowertrain

Code typeSubaru specific

SeverityMedium

Fix difficultyIntermediate

AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

The engine may crank but not start, or may not crank at all depending on the failure mode.
The check engine light is illuminated, often with no other noticeable drivability issues.
Intermittent no-start condition, especially in cold or damp weather.
The starter may not engage when the key is turned to the start position.
Other electrical accessories may work normally, masking the underlying issue.

Common causes, most likely first

Corroded or loose electrical connector at the starter switch or ignition switch.
Damaged or chafed wiring in the starter switch circuit, often near the steering column or firewall.
Faulty ignition switch internal contacts causing high resistance.
Blown fuse or faulty fuse box connection in the starter circuit.
Poor ground connection for the starter or engine block.
Failed neutral safety switch or clutch pedal position sensor (on automatic or manual transmissions respectively).

How to diagnose and fix it

Check the battery voltage and state of charge; a weak battery can cause low voltage on the starter circuit.
Inspect and clean the starter switch connector and ignition switch terminals for corrosion or looseness.
Test the starter switch circuit for continuity and voltage drop using a multimeter, following the factory wiring diagram.
Check all fuses related to the starter circuit and replace any that are blown.
Verify the ground connections at the starter and engine block are clean and tight.
Test the ignition switch operation with a multimeter to ensure it sends proper voltage in the start position.
If the circuit and switch test good, check the neutral safety switch or clutch pedal position sensor for proper operation.

Starter Switch Circuit Low Input: Hidden Causes

A common oversight is a weak battery or poor battery connections that cause voltage drops only under cranking load, setting P1518 without any other symptoms.
The starter switch circuit often shares a fuse with other circuits, so a blown fuse may cause multiple electrical issues, but P1518 is the only code stored if the ECM is the only module monitoring that circuit.
On some Subaru models, the starter switch signal is routed through the body control module (BCM), so a faulty BCM or its connectors can mimic a starter switch circuit problem.
Aftermarket alarm systems or remote starters spliced into the starter circuit are frequent culprits for low voltage inputs and should be inspected for poor connections.
The code can set intermittently due to vibration or temperature changes affecting a marginal connection, so a wiggle test of the harness while monitoring live data is essential.

Can I keep driving with P1518?

If the vehicle starts and runs normally, you can drive it to a repair shop, but avoid turning the engine off if you suspect the no-start condition may leave you stranded. If the engine cranks but does not start, do not continue cranking excessively to prevent starter damage; have the vehicle towed.

Tools that help

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