P0175 on the 2018 Nissan Altima: Causes and Fixes
The 2018 Nissan Altima came with either the 2.5L QR25DE inline-four or the 3.5L VQ35DE V6. The P0175 code indicates System Too Rich on Bank 2. On the four-cylinder, this relates to the ECM's secondary fuel trim zone. On the V6, Bank 2 is the front cylinder bank (cylinders 1, 3, 5). With 2018 models now having 60,000-100,000+ miles, several age-related components commonly trigger this code.
Symptoms You Might Notice
- Check engine light is on
- Gas mileage has decreased noticeably
- Engine runs rough at idle
- Black exhaust smoke, especially on cold starts
- Fuel smell from the tailpipe or engine bay
- Spark plugs fouling prematurely
Most Common Causes
1. Dirty MAF Sensor (High Likelihood)
At 60,000+ miles, the 2018 Altima's MAF sensor has been exposed to significant contamination. The QR25DE is known for oil consumption issues that accelerate MAF fouling through the PCV system. On the VQ35DE V6, the larger airflow volume means even small calibration errors in the MAF reading create substantial fuel delivery mistakes. Both engines benefit from MAF cleaning as a first diagnostic step. If cleaning doesn't resolve the issue, the sensor itself may need replacement -- especially if it has been contaminated repeatedly over the years.
2. Worn Oxygen Sensors (High Likelihood)
Oxygen sensors have a typical service life of 80,000-100,000 miles. On the 2018 Altima, the upstream O2 sensors may be nearing or past their effective lifespan. A sluggish sensor with increased response time will cause the ECM to overcorrect fuel delivery. On the VQ35DE, the Bank 2 upstream sensor sits on the front exhaust manifold and is exposed to significant heat, accelerating degradation. Test response time with a scan tool -- anything over 150ms indicates a tired sensor.
3. Leaking Fuel Injectors (Medium Likelihood)
Years of use and heat cycling cause injector seals and pintles to wear. On the QR25DE, port fuel injectors can develop drip leaks. On the VQ35DE, the injectors are positioned differently and may experience carbon buildup around the tips. Either condition allows unmetered fuel into the cylinders. An injector balance test will identify which cylinder is receiving excess fuel. On the V6, fuel injector cleaning service can sometimes restore proper operation.
4. Failing Fuel Pressure Regulator (Low Likelihood)
The fuel pressure regulator maintains proper rail pressure. On the 2018 Altima, the regulator diaphragm can deteriorate with age, allowing excessive fuel pressure. Connect a fuel pressure gauge and compare readings to the factory specification of approximately 51 psi for the QR25DE. Pressure that continues to rise after the engine is turned off indicates a leaking regulator.
CVT Considerations
The 2018 Altima's Xtronic CVT is particularly sensitive to engine power output variations. When running rich, the engine produces less power than the TCM expects, causing the CVT to adjust ratios more frequently. Owners may notice the CVT "surging" or RPMs fluctuating more than normal. This is the CVT trying to maintain vehicle speed with compromised engine performance. Resolving the P0175 eliminates these secondary CVT symptoms.
Diagnostic Steps
- Scan all codes. On the VQ35DE, check for Bank 1 codes (P0172) as well to determine if the issue is engine-wide.
- Review fuel trim data. LTFT values beyond -10% confirm consistent over-fueling.
- Clean the MAF sensor with proper cleaner.
- Test O2 sensor response time and voltage range.
- Perform fuel pressure and injector tests.
- Check for vacuum leaks that could affect the MAP or MAF readings.
Repair Cost Breakdown
MAF cleaning: $10-$15. MAF replacement: $100-$230. O2 sensor: $150-$300 per sensor. Fuel injectors: $120-$300 each. Fuel pressure regulator: $200-$450. A full diagnostic at an independent shop runs $80-$130.