P0173 — Fuel Trim Too Rich (Bank 1)
Drive with caution — fix soon.
What P0173 means
This code means the computer has detected that bank 1 is running too rich, with more fuel in the mixture than it should have, and it can no longer trim it back to normal. Common causes include a leaking fuel injector, high fuel pressure, a faulty oxygen sensor, or a dirty mass airflow sensor. It's a common code and usually fixable once a technician pinpoints why the mixture is too rich.
Common symptoms
- Check engine light is on
- Poor fuel economy
- Black smoke from the exhaust
- Rough idle or engine hesitation
- Strong smell of gasoline
Common causes
- Leaking or stuck-open fuel injector
- Excessive fuel pressure or faulty regulator
- Faulty oxygen (O2) sensor
- Dirty or failing mass airflow (MAF) sensor
- Clogged or dirty air filter
Typical repair cost
$100 – $650
Varies by vehicle and root cause.
Frequently asked questions
Can I keep driving with a P0173 code?
Usually yes for short trips, but it's not ideal. A too-rich mixture wastes fuel and can foul spark plugs or harm the catalytic converter, so have it diagnosed within a week or two.
How much does it cost to fix a P0173?
Simpler fixes like a new air filter or cleaning a MAF sensor may cost around $100, while replacing a fuel injector, pressure regulator, or oxygen sensor can run up to about $650.
Is a P0173 code serious?
It's moderate. The car typically still drives, but a rich condition can damage emissions parts and waste gas, so it's worth fixing promptly rather than ignoring it.
What does 'running too rich' mean?
Running rich means there's too much fuel and not enough air in the mixture. The computer normally trims this out, but a P0173 means the imbalance is beyond what it can correct.