P1148
Closed Loop Control Function Bank 1
Get Your FREE AI Diagnostic Report
Enter your vehicle for a personalized diagnosis for code P1148
The P1148 code is specific to Nissan and Infiniti vehicles and indicates that the engine control module (ECM) is unable to enter closed-loop fuel control on Bank 1 (the bank containing cylinder #1). In closed-loop mode, the ECM continuously reads the upstream air/fuel ratio sensor and adjusts the fuel mixture for optimal efficiency and emissions. When this sensor fails or its signal is disrupted, the ECM stays in open-loop mode, running a pre-programmed rich fuel mixture.
You'll likely notice reduced fuel economy, a rough or surging idle, and possible hesitation when accelerating. The exhaust may smell richer than usual. While the vehicle is generally safe to drive short distances, prolonged driving in open-loop mode wastes fuel and can damage the catalytic converter over time.
The most common fix is replacing the upstream air/fuel ratio sensor on Bank 1. Before purchasing a new sensor, inspect the wiring harness and connector for damage or corrosion, and check for exhaust leaks near the sensor location. On V6 Nissan engines, Bank 1 is typically the rear bank closest to the firewall. A quality aftermarket sensor costs $80–$200, while a dealership repair with labor typically runs $200–$500.
Severity
Symptoms
- •Check engine light is on
- •Rough or fluctuating idle
- •Noticeably worse fuel economy
- •Hesitation or stumble during acceleration
- •Occasional engine surging at steady speed
- •Exhaust may smell richer than normal
Likely Causes
The upstream A/F ratio sensor on Bank 1 is the most common failure. When it degrades or fails, the ECM cannot enter closed-loop operation and sets this code.
Damaged, corroded, or shorted wiring between the ECM and the Bank 1 upstream A/F sensor prevents the signal from being read correctly.
A significant exhaust leak before the sensor introduces outside air, causing incorrect readings that prevent closed-loop operation.
In rare cases, the engine control module itself may have a fault in the closed-loop logic or a corrupted calibration, especially after battery disconnects or reflash failures.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Replace the upstream air/fuel ratio sensor on Bank 1
- Inspect and repair wiring and connectors to the A/F sensor
- Check for and repair exhaust leaks upstream of the sensor
- Clear codes and verify closed-loop operation with a scan tool