What P0174 Means on Your 2018 GMC Sierra
A P0174 code on your 2018 GMC Sierra tells you that Bank 2 is running too lean. The 2018 Sierra offers the 4.3L V6 (285 hp), 5.3L V8 (355 hp), and 6.2L V8 (420 hp). On V-configuration engines, Bank 2 is the driver side (left side). The ECM has detected that fuel trim corrections on that bank exceed normal parameters.
At the 2018 model age, the Sierra likely has significant mileage. Wear-related issues with gaskets, sensors, and fuel system components become more common. Let's identify the likely cause.
Symptoms
- Check engine light on
- Rough idle
- Reduced acceleration power
- Increased fuel consumption
- Engine hesitation or stumbling
- Possible knocking under load
Most Common Causes
- Intake Manifold Gasket Leak (30% likelihood) – GM V8 intake manifold gaskets are a known wear item. Over time, the seal degrades and allows vacuum leaks, especially around the rear of the manifold.
- MAF Sensor Degradation (25% likelihood) – After years of service, the MAF sensor loses accuracy. Oil contamination from the PCV system accelerates wear.
- Fuel Injector Wear (25% likelihood) – At higher mileages, injectors can become partially clogged or develop spray pattern issues. AFM-equipped engines stress injectors more.
- Exhaust Manifold Leak (20% likelihood) – Manifold bolts can loosen or break over time, especially on the driver side where heat exposure is intense.
Diagnosis
- Compare bank fuel trims – Isolate whether the issue is Bank 2-specific or system-wide.
- Smoke test – The most reliable method for finding intake leaks on a GM V8.
- Clean and test MAF – A quick cleaning may resolve the issue if contamination is the cause.
- Injector balance test – Check each Bank 2 injector for proper flow.
- Exhaust inspection – Look for soot, listen for ticking on cold starts.
Repair Costs
- Intake manifold gasket – $300–$650 parts and labor.
- MAF sensor – Cleaning: $10. Replacement: $70–$200.
- Fuel injectors – Cleaning: $100–$200. Single replacement: $100–$250 plus labor.
- Exhaust manifold – Gasket: $150–$300. Manifold: $300–$700.
DIY Feasibility
The 2018 Sierra's engine bay is spacious and DIY-friendly. MAF cleaning is a 15-minute job. Intake manifold gasket replacement on GM V8s is a common DIY project with plenty of guides available. Exhaust manifold work may require penetrating oil and an extractor set for seized bolts. Allow a full day for intake gasket work.
Prevention
- Use quality oil and change on schedule to reduce PCV contamination
- Replace the air filter every 20,000–25,000 miles
- Use Top Tier gasoline
- Clean MAF sensor every 30,000 miles as maintenance
- Consider intake manifold gasket replacement proactively at 100,000+ miles