P0172 (generic)
System Too Rich (Bank 1)
System: Powertrain · Fuel & Air Metering
Severity: moderate · Inspection: often fails
Description
Too much fuel relative to air on Bank 1. Common causes: leaking fuel injector, high fuel pressure, faulty oxygen sensor, contaminated MAF, restricted air filter.
Diagnostic snapshot P0172
- Difficulty
- 6/10 — Intermediate diagnostics
- Est. repair cost
- $40 – $450 (parts + typical shop labor)
- Common symptoms
- Check engine light (MIL)
- Rough idle
- Poor fuel economy
Diagnostic workflow
- Confirm P0172 with a live scan — note pending vs stored and freeze frame data.
- Verify reported symptoms: Check engine light (MIL), Rough idle, Poor fuel economy.
- Inspect wiring/connectors and related sensors before replacing modules.
- Most likely fixes: Diagnose and repair vacuum / air leak; Replace oxygen sensor(s); Clean or replace MAF sensor.
- Clear codes and road-test; re-scan after two drive cycles if the monitor must set.
Topics
- OBD-II and scan tools (guide)
- Powertrain DTCs (P-prefix) (system)
Related symptoms
- Check engine light (MIL) (weight 0.820)
- Rough idle (weight 0.720)
- Poor fuel economy (weight 0.550)
Common fixes (curated)
- Diagnose and repair vacuum / air leak (rank 1)
- Replace oxygen sensor(s) (rank 2)
- Clean or replace MAF sensor (rank 3)
Related articles
Diagnostic bundle (JSON)
Machine-readable graph: related codes, symptoms, fixes, topics, articles, and curated sources rows. Append &external=1 for optional YouTube / Google CSE hits when API keys are configured (see web/.env.example).