# P0172 — System Too Rich (Bank 1)

> ClearTheCode diagnostic code reference (not OEM service data).

Source: https://clearthecode.com/codes/P0172

**System:** Powertrain · Fuel & Air Metering

**Severity:** moderate

## 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

- **Difficulty:** 6/10 — Intermediate diagnostics
- **Est. repair cost:** $40 – $450
- **Common symptoms:** Check engine light (MIL), Rough idle, Poor fuel economy

## Diagnostic workflow

1. Confirm P0172 with a live scan — note pending vs stored and freeze frame data.
2. Verify reported symptoms: Check engine light (MIL), Rough idle, Poor fuel economy.
3. Inspect wiring/connectors and related sensors before replacing modules.
4. Most likely fixes: Diagnose and repair vacuum / air leak; Replace oxygen sensor(s); Clean or replace MAF sensor.
5. Clear codes and road-test; re-scan after two drive cycles if the monitor must set.

## Likely fixes

1. **Diagnose and repair vacuum / air leak** (moderate)
2. **Replace oxygen sensor(s)** (easy)
3. **Clean or replace MAF sensor** (easy)

## Related articles

- [P0172 field guide: system too rich (Bank 1)](https://clearthecode.com/articles/p0172-system-rich-bank1-field-guide)