What Does P0172 Mean on Your 2021 GMC Yukon?
A P0172 code on your 2021 GMC Yukon means the engine control module has detected a rich fuel condition on Bank 1. The 2021 Yukon (T1XX platform) comes with the 5.3L L84 V8 or the 6.2L L87 V8, both featuring direct injection and Dynamic Fuel Management (DFM). Bank 1 is the driver's side cylinder bank.
The Yukon is a premium full-size SUV, and a rich condition affects both its fuel economy and its emissions output. With these large V8 engines, running rich can be especially costly at the pump.
Symptoms You Might Notice
- Check engine light illuminated
- Increased fuel consumption
- Rough or uneven idle
- Black smoke from the exhaust
- Strong fuel odor at the tailpipe
- DFM system may not function optimally
Common Causes of P0172 on the 2021 GMC Yukon
- Contaminated MAF Sensor — The Yukon's V8 engines are sensitive to MAF sensor accuracy. Contamination leads to airflow underestimation and over-fueling.
- Stuck-Open EVAP Purge Valve — A common issue on GM vehicles. The purge solenoid fails and allows continuous fuel vapor flow into the intake manifold.
- Failing O2 Sensor (Bank 1, Sensor 1) — A degraded upstream oxygen sensor provides poor feedback for fuel trim correction.
- Leaking Fuel Injector — Direct injection fuel injectors can develop internal leaks, delivering unmetered fuel.
How to Diagnose the Problem
- Scan all DTCs — Check for P0175, MAF codes, O2 sensor codes, or EVAP codes.
- Review fuel trim data — Compare Bank 1 and Bank 2 LTFT. Both banks rich points to a system-wide cause.
- Test MAF sensor output — Verify readings against GM's specifications for your engine.
- Command-test the purge valve — Use bidirectional control to verify proper sealing.
- Monitor O2 sensor performance — Check voltage and switching frequency.
- Check fuel injectors — Fuel injector balance test to identify leaking units.
Repair Options and Cost Estimates
- MAF Sensor Cleaning — DIY: $10-$15. Shop: $65-$130.
- MAF Sensor Replacement — Parts: $80-$195, labor: $65-$130. Total: $145-$325.
- Purge Valve Replacement — Parts: $25-$65, labor: $65-$130. Total: $90-$195.
- O2 Sensor Replacement — Parts: $80-$210, labor: $100-$190. Total: $180-$400.
- Fuel Injector Replacement — Parts: $60-$175, labor: $260-$475. Total: $320-$650.
Can You Fix This Yourself?
MAF sensor cleaning is a quick DIY task. The purge valve is also accessible on the Yukon's V8 engines. O2 sensor work requires getting under the vehicle. Injector replacement on the direct-injection V8 is more complex and typically warrants professional service.
Prevention Tips
- Use OEM or quality dry air filters
- Follow GM's recommended maintenance schedule
- Use Top Tier gasoline to keep the fuel system clean
- Monitor fuel economy trends — a sudden drop may indicate a developing problem