Where are the spark plugs located?
Spark plugs are located in the cylinder head of most gasoline engines, typically accessible from the top or side of the engine, and in many modern cars each plug has its own ignition coil (coil-on-plug).
The exact position depends on the engine design and ignition system. Inline, V, and boxer configurations place plugs in different sections of the cylinder head, sometimes under intake components or near the valve cover. This article explains the common placements and how to identify them on your vehicle.
Common locations on modern engines
The following layouts describe where you’ll typically find spark plugs on contemporary passenger cars.
- Top-of-head access with plugs threaded directly into the cylinder head, often paired with coil-on-plug assemblies that sit just above each plug.
- Side or rear access in engines where the spark plug wells are built into the cylinder head and the coils or wires route to the plugs from the side of the engine bay.
- Under the intake manifold or valve cover in engines where plugs sit deeper in the head and require removing components to reach them.
- In some transverse-mounted or space-constrained engines, plugs may be tucked under ancillary components, requiring disassembly to access.
In practice, most modern engines place spark plugs in the cylinder head with varying access paths depending on whether the car uses coil-on-plug or coil packs. If you’re planning maintenance, check the service manual for your exact model and engine code to confirm the access points.
Ignition system configurations and accessibility
Across different ignition designs, the way plugs are fed and accessed changes. The following configurations illustrate how these systems influence plug placement and maintenance.
- Coil-on-Plug (COP): Each cylinder has its own ignition coil mounted directly over the spark plug, placing the plug in the head and the coil nearby. This design often provides straightforward plug access from the top.
- Coil packs with plug wires: A single or multiple coils feed sets of plugs through high-tension wires. Plugs are still in the cylinder head, but access may require maneuvering wires and components around the valve cover or intake manifold.
- Distributor-based or wasted-spark systems (older or specialty engines): One or more coils send sparks to multiple plugs via a distributor or shared wiring. Plugs remain in the head, but ignition routing is grouped, which can affect accessibility.
Understanding your ignition system helps you anticipate how easy or difficult plug access will be during replacement or diagnostics. For most modern vehicles, the COP layout offers the clearest access path, while older designs may require more component removal.
How to locate the spark plugs in your vehicle
To find the exact locations on a specific car, start with the owner’s manual or service manual and look up the engine code. Inspect the top of the engine for individual coil packs or a coil-on-plug assembly over each cylinder. If the plugs aren’t visible from the top, follow the ignition wires or coils to see which cylinder heads they feed. In some engines, you may need to remove cosmetic covers or intake components to gain access.
Safety and maintenance notes
Always perform maintenance with the engine cool and disconnect the battery when working near electrical components. If you’re unsure about access points or replacement procedures, consult a qualified technician. Improper handling can cause damage to ignition coils, fuel rails, or intake components.
Summary
Most spark plugs in modern gasoline engines live in the cylinder heads, with access paths that vary by engine design. Coil-on-plug configurations place coils directly over each plug, while other setups use coil packs or older distributor-based systems. To locate the exact plugs on your vehicle, consult the manual and inspect the engine bay for the cylinder head, coils, and any covers that may conceal the plugs. When in doubt, professional guidance ensures safe and correct servicing.
