What are the P1148 Code Symptoms and Causes? | How to Fix P1148?

Your vehicle engine consists of multiple parts and sensors. Whenever any of these sensors go bad, the engine sends a signal to the powertrain control module (PCM). Whenever your PCM/ECM notices a problem with your Air/fuel ratio sensor, it triggers the P1148 code. The P1148 code is a manufacturer-specific diagnostic trouble code (DTC) related to Nissan and Infiniti vehicles. This article explains the P1148 code meaning, symptoms, and causes.

P1148 Code Definition

The trouble code P1148 stands for “Closed Loop Control Function Bank 1”.

What does the P1148 Code Mean?

The P1148 code indicates that your powertrain control module (PCM) detects an issue with the closed-loop control function of the Bank 1 air/fuel ratio sensor.

P1148 Code

In the definition, Bank 1 indicates the side of the engine that contains the cylinder number. 1 and “closed loop” indicates a condition where the PCM uses input data from a sensor.

Like conventional oxygen sensors, air/fuel ratio sensors are fitted with heater elements, whose function is to bring the sensor up to operating temperature, which is up to 1380°F (750°C).

Note that the heater element is controlled via a dedicated control circuit and that pulse modulation is used to control the sensors’ temperature very accurately since the sensor’s operation depends on its operating temperature being within the range specified by the manufacturer.

The temperature of the air/fuel sensor is very important for its efficient working. The precise air-fuel ratio is also crucial for the efficient working of the engine.

Your car’s PCM/ECM is connected to multiple sensors. It takes data from the sensors and utilizes it to control different engine functions. As your PCM doesn’t receive sufficient information from the air/fuel ratio sensor located at Bank 1, it triggers the P1148 engine code.

Symptoms of P1148 Code

  1. Poor fuel economy
  2. A reduction in engine performance
  3. Check Engine Light illumination
  4. Rough idle
  5. Unstable idling
  6. Engine stumble or hesitation on acceleration
  7. Vehicle starting issues
  8. Idling speed may beat the minimum or maximum acceptable speed

Causes of P1148 Code

The following are the most common causes that trigger the P1148 code:

  • Bad “tuning” resistor in the sensor connector
  • Exhaust leak near the A/F ratio sensor
  • Damaged cables or harness
  • Contaminated A/F ratio Sensor
  • Faulty air/fuel ratio sensor
  • Contaminated A/F ratio sensor due to carbon, oil, or silicone-based compounds in aftermarket anti-freeze and oil/fuel additives
  • Damaged sensor connector
  • Faulty PCM (rear)

Read More: P06DD Code Symptoms and Causes

How to diagnose the P1148 Code?

To diagnose the P1148 DTC code, perform the below-given steps:

  1. Use a scan tool to verify the presence of the P1148 trouble code.
  2. Record all stored fault codes, along with all available freeze frame data. This information could be very helpful if an intermittent fault is diagnosed later on.
  3. Inspect the exhaust
  4. Check all the wirings connected to the Air/Fuel ratio sensor. Check for corroded, burnt, disconnected, shorted, or damaged wiring.
  5. Inspect all the connectors in the circuit
  6. Use a scan to determine the sensor output
  7. Perform reference continuity, resistance, voltage, and ground connectivity checks on all wiring. During this step, disconnect the sensor from the PCM to prevent controller damage.
  8. Follow the manufacturer’s guidance to test the air/fuel ratio sensor.

Common P1148 Code Diagnosis Mistakes

  • Replacing the Air/Fuel ratio sensor without inspecting the wiring and connectors
  • Insufficient inspection of all the wiring and connectors for damage
  • Improper testing of the Air/Fuel ratio sensor
  • Failing to check for exhaust leaks
  • Improper diagnosis of the PCM

Repair Cost of P1148 Code

The repair or fixing cost of the P1148 code varies according to the vehicle model, labor cost, and the cause of the problem. To fix or repair the P1148 code, you may need one or more of the following repairs:

PCM replacement$1100 to $1300
Exhaust Leak Repair$80 to $820
Air/Fuel ratio sensor replacement$150 to $390

How serious is the P1148 Code?

The P1148 code is considered a serious diagnostic trouble code. The car may fail to start if it has a P1148 trouble code. This code may lead to poor engine performance and poor fuel economy. It may cause serious drivability problems and may lead to engine damage if not fixed on time.

FAQ Section

What is the air-fuel ratio sensor?

The air-fuel ratio sensor monitors the oxygen content in the exhaust stream and sends data to the computer so that it can add or subtract fuel. If there is any problem with the sensor, it can send a bad or false signal to the computer, which can throw off its calculations and cause it to waste fuel excessively.

What repairs can fix the P1148 Code?

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

What is a bank 1 O2 sensor?

It is the sensor that measures the oxygen content in the exhaust, providing input to the computer, which determines how to adjust the air/fuel ratio.

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