GMC Sierra 3500HD Ignition and Engine Management: 4 Symptoms Worth Taking Seriously (2020-2025)

Most ignition and engine management problems announce themselves well before they strand anybody. On a 2020-2025 Sierra 3500HD, these are the ones worth acting on.

1. A misfire code that follows the coil when you swap it to another cylinder

It rarely gets better on its own, and it usually gets louder before it gets expensive. Start by looking at camshaft position sensors.

2. Fuel economy that drifts down a mile or two per gallon over a few months

It rarely gets better on its own, and it usually gets louder before it gets expensive. Start by looking at spark plugs.

3. A check engine light that flashes under load, which means raw fuel is going into the converter

This is the symptom people put off longest and regret most. Start by looking at ignition coils.

4. A rough idle that smooths out above 2,000 rpm

This is the symptom people put off longest and regret most. Start by looking at spark plugs.

What to Do Next

Iridium plugs on most modern GM engines are a 90,000 to 100,000 mile item. Coils are replaced on failure, not on a schedule.

The same nameplate can have three different engines in one model year. VIN is the only reliable way to get the right plug.

We are a factory GM dealer, not a reseller, so what you order is the same part the service drive installs. Browse our GMC OEM parts catalog or search for Sierra 3500HD spark plugs.