P0172 - System Too Rich Bank 1
P0172 is a generic powertrain diagnostic trouble code indicating System Too Rich Bank 1. It relates to the Fuel & Air Metering system.
DTC Breakdown (SAE J2012)
| System | Powertrain (P) |
| Type | Generic |
| Subsystem | Fuel & Air Metering |
| Fault Index | 72 |
| Standard | SAE J2012 / ISO 15031-6 |
What does diagnostic code P0172 mean?
The engine computer has detected a rich fuel mixture on Bank 1, meaning there is too much fuel or not enough air. The computer has pulled fuel correction to its limit.
Severity Level & Driveability Details
Severity: Moderate
An overly rich engine dumps unburned fuel into the exhaust, which can rapidly melt the catalytic converter, foul spark plugs, and build up heavy carbon deposits.
Common Symptoms of P0172
- Rotten egg or heavy raw gasoline smell from exhaust.
- Black smoke from the tailpipe under acceleration.
- Engine flooding or hard starting.
- Poor fuel economy on Bank 1 rich condition.
- Rough running engine at idle due to rich fuel trims on Bank 1.
Typical Causes for P0172
- Stuck-open or leaking fuel injector on Bank 1.
- Failed fuel pressure regulator (causing excessively high fuel pressure).
- Restricted engine airflow (a heavily clogged engine air filter).
- Faulty engine coolant temperature (ECT) sensor making computer think engine is frozen.
- Stuck-open EVAP canister purge valve.
Diagnostic and Troubleshooting Steps
Check fuel trims on a scan tool (negative fuel trims, e.g. -15% or worse). Test fuel pressure at the fuel rail using a mechanical gauge. Check ECT sensor temperature accuracy on the scanner.
Typical Repairs and Fixes
- Replacing a leaking or stuck fuel injector on Bank 1.
- Replacing the fuel pressure regulator to fix Bank 1 rich condition.
- Replacing a clogged engine air filter.
- Replacing the EVAP purge solenoid valve.
Sensor Location & Parts Involved
The fuel injectors and pressure regulator are mounted on the fuel rail on Bank 1 of the engine.
Clearing Code & Recurrence
Clear the code using an OBD2 scanner to verify that short-term fuel trims on Bank 1 stabilize.
Emissions & Smog Inspection Impact
Increases tailpipe emissions of carbon monoxide (CO) and unburned hydrocarbons from Bank 1.
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Related Diagnostic Codes
Sources & References
This diagnostic guide is compiled and verified against the following authority sources:
- EPA Fuel Economy and Emissions Page
- NHTSA Technical Bulletins
Frequently Asked Questions about P0172
What does the Bank 1 fuel trim rich code P0172 mean?
The engine computer logged P0172 because it detected that the air-fuel mixture is too rich on Bank 1, meaning there is too much fuel or not enough air in the cylinders.
Is it safe to drive with the Bank 1 fuel trim rich code P0172 active?
Yes, but repair Bank 1 rich running promptly to save the catalytic converter.
How much does it cost to repair a Bank 1 fuel trim rich code P0172 fault?
Air filter replacement is $30. Purge valve replacement is $150-$250. Injector replacement on Bank 1 ranges from $250 to $600.
What are the common causes of the Bank 1 fuel trim rich code P0172?
Trigger conditions for the Bank 1 fuel trim rich code P0172 include: Leaking or stuck-open fuel injectors on Bank 1., Excessive fuel pressure due to a failed fuel pressure regulator on Bank 1., Restricted engine air intake (heavily clogged engine air filter)..
Can I clear the check engine light for Bank 1 fuel trim rich code P0172?
Clear the code using an OBD2 scanner to verify that short-term fuel trims on Bank 1 stabilize.
Will the Bank 1 fuel trim rich code P0172 cause an inspection failure?
Increases tailpipe emissions of carbon monoxide (CO) and unburned hydrocarbons from Bank 1.