P1148 Code Nissan: Causes, Symptoms, and How to Fix

This article will explain what a P1148 error code indicates, list the main causes and explain what you can do to fix it.

If your Nissan throws code P1148, it means there is a problem with the air-fuel ratio sensor. The Engine Control Module (ECM) does not get accurate information from this sensor to control engine functions.

An active P1148 error code is accompanied by low fuel economy, rough idling, check engine light, reduced engine performance, and other related issues. The cause can be anything related to the air-fuel ratio sensors. Still, a faulty powertrain module can also be a culprit.

This post focuses on what the P1148 code means, its causes, its symptoms, and how to fix it. Read on for details.

What Does P1148 Code Mean?

P1148 is a manufacturer-specific code meaning closed-loop control function bank1. It is set when the powertrain control module (PCM), or ECM, detects a problem with the closed loop function of the engine’s bank 1 air-fuel ratio sensor.

p1148 code nissan

Bank 1 indicates the side of the engine with the cylinder designated number 1, and a closed loop means PCM uses input data from the sensor. If this sensor is faulty, PCM will receive out-of-range data. The P1148 DTC code is, therefore, set.

Causes of P1148 Nissan Code

The causes of this error code depend on your car model year. For Nissan models 2005 and up, the most common causes include the following:

  • Faulty Air Fuel Ratio Sensor 1 Bank 1
  • Air Fuel Ratio Sensor 1 Bank 1 circuit is open or shorted
  • Air Fuel Ratio Sensor 1 Bank 1 circuit electrical connection

But if you drive an older model, the causes can be any of the following:

  • Faulty Heated Oxygen Sensor 1 Bank 1
  • Heated Oxygen Sensor 1 Bank 1 circuit is open or shorted
  • Heated Oxygen Sensor 1 Bank 1 circuit electrical connection

However, there are some universal causes of DTC P1148 that may cut across all model years. Let’s describe each in detail!

Faulty Air Fuel Ratio Sensor 1 Bank 1

There are two air-fuel ratio sensors mounted on the exhaust system. They continually monitor the air-fuel ratio and send a signal to the ECM so that it can adjust fuel injection and timing for maximum engine efficiency and power. These sensors offer a higher level of sensitivity than the traditional oxygen sensor, allowing ECM to respond to the engine needs more precisely.

upstream and downstream o2 sensors
Source: Functions of Oxygen Sensors in Exhaust Systems

But with a faulty air-fuel ratio sensor, the ECM has no way of knowing the imbalance and therefore does to make the adjustment. The engine may run lean or rich and with reduced performance. The ECM detects the fault when it receives erroneous data from the sensor and sets the error code P1148.

Damaged Wiring Harness

The air-fuel ratio sensors and ECM communicate in a circuit through a wiring connection. The wire bundles or harness may get damaged, causing either a short or an open circuit. That disrupts the data flow or power supply to the vital components. The closed loop function bank 1 will be interrupted, causing the ECM to activate code P1148.

Air Fuel Ratio Sensor 1 Bank 1 Circuit Electrical Problems

Electrical problems can also disrupt the normal function of the sensor. Its electrical or electronic components can be damaged or fail to function as intended. That means it will inaccurately measure the oxygen level in the air-fuel mixture, which leads to erroneous data being sent to the ECM. The ECM, in turn, sets the code P1148.

Exhaust Leak Near the Air/Fuel Ratio Sensor

The upstream and downstream air-fuel sensor data are compared for any significant difference. If there is an exhaust leak somewhere in the exhaust system, the accuracy of the information differs. What the front sensors measure will vary from that of the downstream sensor. The difference, if significant enough, makes ECM activate code P1148.

Contaminated A/F Ratio Sensor

Air-fuel ratio sensors can be contaminated by engine coolant leaks or phosphorus if the engine is burning oil. The leakages can result from damaged head gaskets or cracks in the cylinder head. It can also be due to the carbon or silicon-based compounds in the anti-freeze oil.

A contaminated air-fuel ratio sensor loses its sensitivity. It will, therefore, give false readings that the ECM detects and sets the error code. Cleaning the sensor can help to restore its functionality, but sometimes you have to replace it.

Blown Fuse of The Sensor

The air-fuel ratio sensors have heating elements to keep them within the operating temperature. ECM regulates the amount of current that flows through these heating elements to help maintain the temperature. And for protection purposes, a fuse disconnects the circuit if excess current flows to the sensor’s heating element.

A blown air-fuel ratio sensor fuse interferes with the function of these sensors. The heater elements fail to bring the sensors to an operating temperature of about 1380°F (750°C). This temperature is very crucial for its operation. And since it does not get heated, the output data will be erroneous, making the ECM detect it as a fault.

Faulty ECM

This is also a possible cause of code P1148, though it is rare. ECM is a vital component of any car. This unit collects data from various engine sensors and processes it to control the engine for maximum performance and efficiency. If there is a problem with any sensor, the ECM sets the code and turns on the check engine light.

However, the ECM can develop faults, making it set the P1148 code erratically. If the check engine light stays on after replacing the sensor and repairing any other possible cause, ECM can be the culprit. A faulty ECM is characterized by the following signs:

  • Check Engine Light
  • Reduced Engine Performance
  • Shifting issues
  • Issues in starting
  • Misfires
  • Failed Emission Test
  • Poor Fuel Economy
  • Code Errors related to PCM

Ask an expert or take the car to the dealership for the ECM to be diagnosed, repaired, or replaced if damaged.  

Possible Symptoms of an Active Code P1148

You can know when your Nissan car has an active error code P1149. Although the symptoms may overlap with other diagnostic trouble codes, you should not ignore the possibility of having p1148 set if you notice the following:

  • Poor fuel economy
  • Reduction in engine performance
  • Check Engine Light warning
  • Rough idle
  • Unstable idling
  • Engine stumble or hesitation on acceleration
  • Vehicle starting issues
  • Higher idling speed than the recommended minimum and maximum speed

How To Fix P1148 Nissan Error Code?

Fixing the error code involves diagnosing the cause and resolving the issue. The steps may vary from one car model to the next, but generally, the following procedure helps:

Use an OBD2 diagnostic tool to read the P1148 code. You should confirm that it is active before further diagnosis. Also, note all other fault codes and freeze frame data. These will help you if there has been an intermittent fault.

  1. Inspect the exhaust for any leakages
  2. Check the wiring harness for physical damage or corrosion. You should also test for the continuity of individual wires to ensure no open circuit. Ensure all connectors throughout the circuit are intact.
  3. Use an OBD2 scanner to read the sensor output and compare it with reference values from the repair manual or a reliable source.
  4. Perform resistance, voltage, continuity, and ground connectivity checks on all the wiring to the sensor. Ensure the sensor is not connected to the ECM during this process to avoid damage. 
  5. Test the air-fuel ratio sensor according to the manufacturer’s instructions to determine if it is damaged.

Fixing the P1148 error code can involve doing any of the following:

  • Replacing the faulty Air/Fuel ratio sensor
  • Repairing the Exhaust leaks
  • Replacing or repairing the damaged connectors
  • Cleaning the dirty Air/Fuel ratio sensor
  • Replacing or reprogramming the PCM
  • Replacing or repairing the damaged and corroded wiring

Once you determine the cause of the P1148 error code from the diagnosis procedure, fix it and clear the error code using the OBD2 scanning tool. You can also wait for the code to disappear in the next initialization when the car performs checks on all systems.  

Average Cost to Fix Code P1148 Nissan

The cost of fixing this error code varies according to the car make and model and the cause. The labor fees also range from location to location. It usually takes about an hour to diagnose the code, costing between $75 and $150.

As mentioned, the repair cost depends on what component you need to repair or replace. For replacing the PCM or ECM, you should expect to pay between $1,100 and $1,300. And for exhaust leak repair, the estimated cost varies widely. You can get away with paying just $80, but it can sometimes be as high as $800. If you have to buy a new air-fuel ratio sensor, your budget should be about $150-$390.

Note that these are just approximations. Don’t freak out if your mechanic tells you to pay more for the repair or fix.

What Should You Do If You Get This Code?

The P1148 is considered a serious DTC. If you have this code, your car may fail to start, or the engine may run erratically. You will experience rough idling, low fuel economy, and reduced performance. So, fix the code at the first opportunity. You can diagnose and fix it yourself in your garage if you are an advanced DIYer. But if you doubt your DIY skills, take the car to a dealership or an auto repair shop for help.

Can I Keep Driving the Car With A P1148 Code?

The severity of a P1148 code is high to severe. You should not attempt to drive the vehicle in order to prevent possible further damage to engine components. Apart from poor MPG and performance, the car might hesitate to start, leaving you stranded away from home. And let me tell you, towing services are not cheap these days!

My recommendation is to get the problem fixed as soon as possible. Unfortunately, it is one of those issues that the longer it waits to be repaired, the higher the repair cost will be.