Quick answer: The P0173 code indicates that your vehicle’s engine control module can no longer manage the air-fuel mixture effectively on Bank 2. This fault directly impacts the fuel and emission systems. While you can drive short distances safely, inspect it promptly to prevent catalytic converter damage and poor fuel economy.
If your check engine light is illuminated and a scan tool returns code P0173, your engine is struggling to maintain the correct fuel-to-air balance on Bank 2. This guide covers what causes this fuel trim code, common symptoms you might experience, and step-by-step diagnostic checks to resolve the problem efficiently.
What Does P0173 Mean?
The powertrain control module (PCM) constantly adjusts the amount of fuel injected into the engine cylinders using feedback from the oxygen sensors. These adjustments are called fuel trims. When the PCM has to add or remove an abnormal amount of fuel to achieve a balanced burn on Bank 2 (the engine bank that does not contain cylinder number one), and it reaches the maximum compensation threshold, it logs trouble code P0173.
Symptoms
- Illuminated check engine light
- Noticeable reduction in fuel efficiency
- Rough or erratic engine idle
- Hesitation, stumbling, or lack of power during acceleration
- Strong exhaust or unburnt fuel odor from the tailpipe
- Occasional engine misfires
Possible Causes
A common mistake is immediately replacing oxygen sensors or the catalytic converter. Fuel trim codes are frequently caused by simpler, less expensive issues affecting air intake or fuel delivery.
- Vacuum leaks, cracked intake boots, or faulty PCV hoses on Bank 2
- Dirty or contaminated Mass Air Flow (MAF) sensor
- Failing Bank 2 upstream oxygen (O2) sensor
- Leaking, clogged, or dirty fuel injector on Bank 2
- Faulty fuel pressure regulator or low fuel rail pressure
- Exhaust leak upstream of the Bank 2 oxygen sensor
Check These Yourself Before Visiting a Mechanic
- Inspect the rubber air intake tube and vacuum lines around Bank 2 for visible cracks, splits, or loose hose clamps.
- Check your engine oil dipstick for the smell of gasoline, which can signal a stuck-open fuel injector.
- Inspect the wiring harness and electrical connector plugged into the Bank 2 oxygen sensor for melted insulation or loose pins.
How to Fix It
- Connect an OBD-II scanner and monitor live data for short-term and long-term fuel trims on Bank 2 to see if the engine is running rich or lean.
- Inspect the intake tract and perform a smoke test to identify and seal any unmetered air leaks.
- Clean the MAF sensor wire carefully using dedicated electronic MAF cleaner spray.
- Check the Bank 2 exhaust manifold for cracks or leaking gaskets that could allow false air to reach the O2 sensor.
- Test fuel system pressure against manufacturer specifications and inspect the vacuum port on the fuel pressure regulator for wet fuel.
- Test the switching speed and voltage of the Bank 2 upstream oxygen sensor; replace if response is slow.
- Inspect, clean, or replace any malfunctioning fuel injectors on Bank 2.
Estimated Repair Costs (2026)
| Job | Parts ($) | Labor ($) |
|---|---|---|
| MAF Sensor Cleaning / Replacement | $15 – $140 | $45 – $90 |
| Vacuum Line / Intake Boot Repair | $15 – $75 | $75 – $160 |
| Upstream O2 Sensor Replacement | $65 – $190 | $70 – $140 |
| Fuel Pressure Regulator Replacement | $45 – $160 | $85 – $160 |
| Single Fuel Injector Replacement | $75 – $220 | $95 – $210 |
Note: These are 2026 estimates in US dollars; actual repair costs vary depending on vehicle make, engine layout, and local labor rates.
Frequently Asked Questions
Can I drive with the P0173 code?
You can drive short distances to get home or to a repair shop. However, prolonged driving with an unbalanced fuel trim can foul spark plugs, overheat the exhaust, and permanently ruin the Bank 2 catalytic converter.
How do I clear the P0173 code?
Once you locate and repair the root cause, you can clear the code using an OBD-II scan tool. Alternatively, the computer will clear the code on its own after completing several driving drive cycles without detecting the fault.
What is the difference between P0170 and P0173?
Both codes represent a fuel trim malfunction. The difference is the cylinder bank: P0170 applies to Bank 1 (the side containing cylinder number one), while P0173 applies exclusively to Bank 2 on V-style or boxer engines.