How Many Solenoids Are in a Car? (+ What They Do)

If you’ve ever had a check-engine light or shifting problem, a mechanic might mention a “bad solenoid.”

But what exactly is it — and how many does your car really have?

A solenoid is an electromechanical device made of a coil and a plunger. It acts like a tiny switch that converts electrical signals into mechanical movement, controlling things like fluid flow, fuel vapor, or mechanical engagement.

Most modern cars have 10–20 or more solenoids, spread across different systems. Let’s look at where they are, what they do, and why that matters.

So…How Many Solenoids Are in a Car?

There’s no single fixed number, but the minimum is 1 — the starter solenoid. The average modern car typically has 10-20+ solenoids, depending on system complexity.

Here’s how that works out:

Transmission design: Older 4-speed autos may use 2–3 solenoids, while newer 8- or 10-speed models can have 10 or more.

Engine technology: Systems like variable valve timing (VVT), turbocharging, and advanced emissions controls each add solenoids.

Safety systems: ABS and traction control rely on multiple solenoids to regulate brake pressure and wheel speed.

Vehicle features and trim level: Air suspension, all-wheel drive engagement, and electronic fuel injection add more solenoids — meaning higher-trim or luxury models can easily top 20+.

The exact count isn’t what matters most — it’s knowing which solenoid is likely failing if you’re seeing symptoms like hard shifting, starting trouble, or rough idling. Let’s explore different types of solenoids to understand their functions.

Transmission Solenoids

These are the solenoids most people hear about. They control how smoothly your transmission shifts.

Quantity (typical): 2–8+, depending on the transmission design.
Types:
- Shift solenoids (2 to 8 units) direct transmission fluid to engage specific gears.
- Lock-up or torque converter solenoid (usually 1) locks the torque converter at cruising speeds to improve fuel efficiency.
Overall role: Regulate hydraulic pressure so your transmission can shift seamlessly.
Failure signs: Slipping gears, delayed or rough shifting, or getting stuck in gear.

If you’ve been told you have a “bad solenoid,” it’s often one of these.

Read more about transmission solenoid replacement and its associated costs.

Starter Solenoids

Every vehicle has a starter solenoid, mounted on or near the starter motor.

Quantity: 1
Function: Acts as a heavy-duty relay that sends power to the starter motor when you turn the key or press start.
Failure signs: A click when you turn the key, no cranking, or silence at the start attempt.

Without it, the electrical connection to the starter can’t engage, so the engine never even begins to turn over.

Emissions and Engine Control Solenoids

Your engine uses several solenoids to manage airflow, emissions, and performance:

1. EVAP Purge Solenoid (fuel vapor):

Quantity: 1
Function: Releases fuel vapor from the charcoal canister into the engine for combustion.
Failure signs: Check engine light, rough idle, or a faint fuel smell.

2. EGR Solenoid (exhaust gas recirculation):

Quantity: 1 (in vehicles with EGR systems)
Function: Recirculates exhaust gas into the intake manifold to reduce nitrogen oxide emissions.
Failure signs: Engine knocking, poor acceleration, or increased emissions.

3. VVT Solenoids (oil control):

Quantity: 1–4, depending on engine configuration.
Function: Adjusts valve timing using oil pressure to boost power and efficiency.
Failure signs: Check engine light, reduced power, rough idle, or decreased fuel efficiency.

The number of these solenoids varies with the engine’s design and emissions setup.

ABS Solenoids

Your anti-lock braking system (ABS) uses solenoids, too—just in a different way.

Quantity: Usually 4–8 (one per wheel circuit, sometimes more in advanced systems).
Function: Modulate brake fluid pressure to prevent wheel lock-up during hard braking.
Failure signs: ABS warning light, inconsistent brake pedal feel, or longer stopping distances.

When one fails, the ABS system can’t regulate pressure properly, reducing traction and control under hard braking.

Other System Solenoids

Beyond the main systems, cars use solenoids in various specialized areas:

1. Air Suspension Solenoid Valves:

Quantity: 1–4 (if equipped).
Function: Control airflow to suspension airbags to adjust ride height and comfort.
Failure signs: Uneven ride height, sagging suspension, or a constantly running compressor.

2. Injector Solenoid Valves:

Quantity: Typically 1 per cylinder (total depends on engine).
Function: Control when and how much fuel is injected into each cylinder.
Failure signs: Engine misfires, poor fuel economy, or rough running.

3. Idle Air Control (IAC) Solenoid:

Quantity: 1 (in some vehicles).
Function: Regulates idle speed by adjusting airflow around the throttle plate.
Failure signs: Irregular idling, stalling at stops, or fluctuating RPMs.

You may also find solenoids in 4WD engagement systems, door locks, or even convertible tops.

Need a Solenoid Repair? AutoNation Mobile Service Has You Covered

Solenoids are everywhere in today’s cars, quietly managing everything from starting your engine to shifting gears and regulating emissions. Of these, starter and transmission solenoids are probably the ones most often diagnosed when problems arise.

If you suspect a failing solenoid, don’t guess. Leave diagnosis and replacement to trained professionals to avoid swapping the wrong part.

Contact AutoNation Mobile Service for expert diagnostics and repair services. You can book online, get service 7 days a week, and enjoy a 12-month / 12,000-mile warranty on repairs.