Spark Plug Maintenance Guide for GM Vehicles (Chevrolet, GMC, Buick & Cadillac)
Spark plugs are a "set it and forget it" part for a long time — until they wear enough to start taking ignition coils and catalytic converters down with them.
Overview & Interval
Spark plugs ignite the compressed air/fuel mixture in each cylinder. GM's iridium plugs are long-life components, typically good for around 100,000 miles under normal driving, though this varies by specific engine and plug design.
Common Problems That Can Develop From Neglect
- Widening spark gap over time, producing a weaker and less consistent spark
- Misfires, rough idle, hesitation, and reduced fuel economy
- Ignition coils working harder and running hotter to fire worn plugs, leading to premature coil failure
- Unburned fuel from prolonged misfires damaging the catalytic converter — one of the most expensive knock-on repairs from this kind of neglect
What Needs to Be Done If It Develops Into a Problem
Replace the worn spark plugs and any ignition coils that have already failed or show damage. If misfires have already damaged the catalytic converter, that needs to be replaced separately.
Repair Cost
- Spark plug replacement: $100 – $400 (higher on V6/V8 engines where plugs sit under the intake manifold)
- Ignition coil replacement (per coil, with labor): $150 – $300
- Catalytic converter replacement: $900 – $2,200+
Can I Drive With This Issue?
A mild, occasional misfire is generally safe to drive on short-term while you schedule a repair. A flashing check engine light means a severe misfire — stop driving as soon as it's safe, since that flashing light specifically warns of catalytic converter damage in progress.
Which OEM Part Fixes It
ACDelco iridium spark plugs matched to your specific engine (41-162, 41-114, 41-103, and similar part numbers vary by application).
Common Mistakes
- Using the wrong heat range or plug type for the engine
- Over- or under-torquing plugs, which can crack the cylinder head or cause poor sealing
- Not checking/adjusting the gap if the plugs aren't pre-gapped from the factory
- Forgetting anti-seize where specified, or over-applying it in a way that affects torque and grounding
- Reinstalling old, damaged coil boots instead of replacing them alongside worn plugs
Frequently Asked Questions
How do I know if it's time to replace my spark plugs?
Rough idle, hesitation on acceleration, reduced fuel economy, or a misfire code are all signs worth checking, even if you haven't hit the mileage interval yet. Iridium plugs are long-lived, but symptoms matter more than mileage alone.
Why do worn spark plugs damage ignition coils?
A widening spark gap forces the coil to generate a stronger spark to jump the gap, which makes the coil work harder and run hotter over time. Left long enough, that extra stress leads to premature coil failure.
Is it worth replacing coil boots even if the coils themselves are fine?
Yes, if they're old, cracked, or brittle. Reinstalling damaged boots on new plugs can let moisture or debris in and cause a misfire shortly after the job, undoing the benefit of the fresh plugs.
Can bad spark plugs really damage a catalytic converter?
Yes. Prolonged misfires send unburned fuel into the exhaust system, where it can overheat and damage the catalytic converter — turning a routine spark plug job you put off into a much more expensive repair.
Browse the full ignition parts lineup at www.gmserviceguy.shop.
Costs and intervals are estimates based on average national rates and typical GM guidance; always check your owner's manual for your specific vehicle.