A Guide to Replacing Ignition Coils on the 2002-2009 GMC Envoy
Understand why your Envoy is misfiring and how to choose the right replacement ignition coil.
- Ignition coil failure is extremely common on the 2002-2009 Envoy, often causing misfire codes (P0301-P0306).
- Check for a water leak from the cowl seal above the engine, as this is a known cause of repeated coil failure, especially in cylinders 3 and 4.
- Replacement is very easy for a DIYer, requiring only basic tools and about 30 minutes.
- For best results, choose OE-equivalent brands like ACDelco or Delphi; if replacing one coil on a high-mileage engine, it's wise to replace them all.
Is Your GMC Envoy Running Rough? It Could Be an Ignition Coil.
Ignition coil failure is a very common issue on the GMC Envoy, especially those with the 4.2L inline-six engine. These coils are responsible for generating the spark that makes the engine run. When one or more coils start to fail, you'll notice symptoms like a rough idle, hesitation when you accelerate, and a loss of power. The Check Engine Light will almost always come on, and it may flash, which signals a serious misfire that could damage other expensive parts.
A Known Water Leak Problem
A well-documented issue on 2002-2009 Envoy and Trailblazer models is a degraded cowl seal at the base of the windshield. This allows water from rain or a car wash to drip directly onto the engine, often shorting out the ignition coil in cylinder #3 or #4. If you repeatedly have failures on these middle cylinders, inspect this seal. Owners have reported that GM has not issued a recall for this, but sealing the cowl area can provide a permanent fix.
🎬 Watch this video to see the permanent cowl seal fix.Choosing the Right Aftermarket Ignition Coil
When replacing coils, you have a choice between OEM and a wide range of aftermarket brands. While one failing coil might tempt you to replace just that one, it's often wise to replace all of them at once on a higher-mileage vehicle, as they have all endured the same conditions and the others may fail soon. It's also the perfect time to replace your spark plugs.
🎬 See a full walkthrough for replacing both plugs and coils.Brand Quality Tiers
- Premium (OE/OEM-Equivalent): ACDelco and Delphi are the top choices for the GMC Envoy. ACDelco is the original GM parts brand, and Delphi was the original equipment manufacturer for many of these parts. In many cases, the Delphi and ACDelco parts are identical. For reliability and performance that matches the factory part, these are your best bet.
- Quality Aftermarket: Brands like Bosch, NGK, Hitachi, and Standard Motor Products (SMP) have a strong reputation for producing quality ignition components. They offer a reliable alternative to the OE brands, often at a slightly lower price point.
- Economy: Brands like DriveWire, TRQ, and various others found in kits on Amazon or eBay offer a significant cost saving, with full sets of six often costing less than a single premium coil. While the low price is appealing, be aware that forum users have reported mixed results and early failures with some budget brands. These can be a viable option for a budget-conscious repair, but may not offer the same longevity as premium brands.
Cost to Replace GMC Envoy Ignition Coils
The cost can vary significantly based on who does the work and the quality of the parts used. Replacement is a very simple job that most owners can do themselves in under an hour with basic tools.
| Item | DIY Cost (Single Coil) | Shop Cost (Single Coil) | DIY Cost (Full Set) |
|---|---|---|---|
| Economy Part | $37 - $60 | Not typically used | $80 - $150 (Set of 6/8) |
| Premium Part | $80 - $125 | $91 - $185 | $480 - $750 (Set of 6/8) |
| Labor | $0 | $98 - $143 | $120 - $200 |
| TOTAL | $37 - $125 | $189 - $329 | $80 - $950 |
Frequently Asked Questions
How do I know which ignition coil is bad?
The easiest way is to use an OBD-II scanner. A code like P0304 indicates a misfire on cylinder 4. To confirm it's the coil, you can swap the coil from cylinder 4 with the coil from cylinder 5, clear the codes, and drive the vehicle. If the code changes to P0305, you've confirmed the coil is the problem.
🎬 Watch how to diagnose and swap a cylinder 4 coil.Is it difficult to replace the ignition coils on my Envoy?
No, this is considered a very easy DIY job. For the 4.2L I6, you only need to remove the plastic engine cover, unplug the electrical connector, and remove one 10mm bolt for each coil. For the 5.3L V8, the coils are held by two 7mm bolts. The entire job for one coil can take less than 30 minutes.
Should I replace all my ignition coils at once?
If your vehicle has high mileage (over 100,000 miles), it's a good idea. The coils have all operated for the same amount of time, so when one fails, others are likely to follow. Replacing them all at once saves you from having to do the same job again in a few months. It's also the perfect time to install new spark plugs.
What is dielectric grease and do I need it?
Dielectric grease is a non-conductive, silicone-based grease that protects electrical connections from moisture and corrosion. It's recommended to apply a small amount inside the spark plug boot of the new coil. This helps seal out moisture and makes it easier to remove the coil in the future.
Helpful Videos
Technical Specifications
OEM Part Numbers: 12568062 19300921 12560862 UF303 UF414
All 2002-2009 GMC Envoy models use a Coil-on-Plug (COP) ignition system. The 4.2L I6 engine uses 6 individual coils. The 5.3L V8 engine uses 8 individual coils. Coils for the I6 and V8 are different parts and are not interchangeable.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- GMC Envoy: