Investigating the P0100 Code on Your 2021 Hyundai Sonata
A P0100 code on your 2021 Hyundai Sonata means the ECM has flagged a malfunction in the Mass Air Flow (MAF) sensor circuit. Your 8th-generation Sonata's 2.5L Smartstream engine relies on precise MAF data for fuel efficiency and performance. With Hyundai's 5-year basic warranty likely still active, your first move should be checking warranty eligibility.
MAF Sensor on the 2021 Sonata
The 2021 Sonata's 2.5L Smartstream MPI engine (191 hp) uses a hot-wire MAF sensor positioned between the air filter and throttle body. After four-plus years, oil vapor from the PCV system gradually contaminates the sensing element—the most common trigger for P0100.
Symptoms
- Check engine light on with P0100
- Hesitation during acceleration
- Rough or fluctuating idle
- Fuel economy below the 28-38 mpg range
- 8-speed automatic may shift erratically
- Possible stalling
Ranked Causes
- Contaminated MAF sensor element (35-40%) — Oil vapor deposits after four-plus years of service.
- Air intake leak (20-25%) — Cracked hose, loose clamp, or worn gasket.
- MAF sensor failure (15-20%) — Internal electronics degradation.
- Wiring or connector issue (10-15%) — Corrosion or damage from environmental exposure.
- Air filter condition (5-10%) — Neglected or damaged filter.
Diagnosis and Repair
- Check warranty — Hyundai's 5-year/60,000-mile basic warranty covers through ~2026. The emissions warranty (8yr/80k) extends through 2029. Contact your dealer.
- If under warranty — Schedule dealer service for no-cost repair.
- If out of warranty — Scan codes, inspect intake, and clean the MAF sensor ($10-15) as first step.
- Monitor live data — Compare readings against Smartstream 2.5L specifications.
Repair Costs
- Under warranty: $0 (likely still covered)
- MAF sensor cleaning: $10-15 (DIY)
- MAF sensor replacement: $110-240 parts, $50-100 labor
- Intake hose: $30-80
- Wiring repair: $80-200