Why is my GMC Sonoma 4.3 misfiring with a flashing check engine light?

Short answer: A flashing check engine light on a Sonoma means a misfire bad enough to damage the catalytic converter. On the 4.3 V6, start with the basics: plugs, wires, distributor cap and rotor. If a multi-cylinder misfire comes back after those, the fuel injectors are a known culprit; that's what fixed one owner's truck.

Symptom: It idles roughly with heavy vibration, the check engine light blinks, and it runs poorly while driving. It may come back months after a tune-up.

What to check first

1. Read the codes. P0300 is a random/multiple misfire; P0301–P0306 name a cylinder.
2. Check plugs, wires, cap and rotor, especially if they've never been replaced.
3. Check fuel filter and fuel pressure.
4. If misfires return after ignition parts, have the fuel injectors tested.
5. Check battery cable connections if lights flicker and electrical items act up too.

Likely causes

1. Fuel injectors. Fixed one 2001 owner's repeat multi-cylinder misfire.
2. Plugs, wires, cap and rotor. The usual first step.
3. Fuel delivery (filter or pressure). Can cause lean misfires.
4. Loose battery or ground connections. Can cause odd electrical symptoms along with running problems.

What it usually costs

No owner in these threads posted a repair price.

Is it safe to keep driving?

No. A flashing check engine light means stop driving soon; continuing can overheat and destroy the catalytic converter. One owner had the truck towed rather than driven. Verify with a mechanic.

DIY or shop?

DIY for plugs, wires, cap and rotor. Injector testing and replacement on the 4.3 is usually a shop job.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA lists no recall for misfires or rough running on the GMC Sonoma in the model years we could check on 2026-10-24 (the recall lookup returned an error for 1 model-year queries). Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• NHTSA complaints: 100 keyword-matched complaints for GMC Sonoma 1996–2004 (of 848 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-24; keywords: misfire, rough, stall, injector, check engine, hesitat). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 2001 GMC Sonoma is misfiring again on Car Talk, a 2001 Sonoma 4.3 V6 had a blinking check engine light and multi-cylinder misfire; plugs, wires and an oxygen sensor fixed it for three months before it came back. A member asked about the fuel filter and fuel pressure. Another 2001 4.3 owner said a cap, rotor, plugs and wires didn't help him. The original owner said it ended up being the fuel injectors.
• In 2002 GMC Sonoma engine light on Car Talk, a 2002 Sonoma 4.3 had its check engine light on and flashing, flickering lights and loose battery cables, then cranked but wouldn't start. A member said a flashing light while running means a serious misfire that can damage the catalytic converter. The owner had it towed to a mechanic rather than drive it.

Quick tip

Don't keep replacing ignition parts if the misfire keeps coming back. Have the injectors checked.

Vehicle focus: 1996–2004 GMC Sonoma (and Chevy S-10) with the 4.3L V6.

Safety / mechanic note

A flashing check engine light means a misfire that can damage the catalytic converter. Verify with a mechanic.