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P0142 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

The OBD-II Code P0142 is for O2 Sensor Circuit Malfunction Low Voltage (Bank 1 Sensor 3). O2 sensors are used to monitor the amount of oxygen in the exhaust gas, which determines how efficiently your engine can burn fuel.

Meaning

A P0142 code is the result of poor flow of electrical current in the heated element (heater) circuit of one or more O2 sensor(s). The front O2 sensors are located in the exhaust manifold. The rear O2 sensor is located in the tailpipe which is being highlighted by this code.

Causes

The following are common causes of this issue:

  • The O2 bank 1 sensor 3 circuit is shorted or open.
  • An exhaust leak before the sensor can cause the code from excessive oxygen getting into the exhaust stream. The O2 sensor bank 1 sensor 3 is downstream of the last catalyst in the exhaust system; an exhaust leak before it might cause the code.

Symptoms

Symptoms of a P0142 trouble code may include:

No symptoms or a small misfire at light load and cruise

A code is often preceded by a "rotten egg" smell from the exhaust, which is due to reduced O2 in the exhaust manifold. Poor gas mileage can also be a symptom of this problem.

Diagnosis

  1. Check for loose connections at the sensor 3 of O2 bank 1
  2. Before replacing the O2 sensor, check the exhaust system for any exhaust leaks.
  3. Scan for codes P0143 and P0144, or if the issue is intermittent and can be ignored unless it recurs.

Common mistakes

The following are common mistakes when diagnosing the trouble code P0142:

  • Replace the O2 sensor without checking for exhaust leaks.
  • Replacing the wrong bank of the O2 sensor
  • Replacing a good O2 sensor with a defective one from another vehicle.

How serious is this?

  • Because the Check Engine Light is on, the vehicle will not pass emissions testing.
  • In most cases, the code will not have a significant impact on how the engine operates.
  •  The exhaust may leak and expose the occupants to harmful gases.

If the problem is the catalyst, this code may indicate an excessive exhaust emission. It's for the sensor located behind bank 1 of the exhaust and might contribute to a high level of emissions if there's a problem with the catalyst.

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Replace the O2 bank 1 sensor 3 
  • Repair or replace exhaust leaks 
  • Clear codes and retest.

No repairs will be necessary if the only symptom is a newly activated Check Engine Light. If one of these conditions exists: The vehicle has passed emissions testing, and there are no symptoms, and no other codes than P0142 exist, this code can be safely ignored.

This code means that there's a problem with the heated element circuit in an O2 sensor somewhere downstream of the catalytic converter. It could have failed due to excessive heat due to misfire, but it could also have failed because of poor fuel quality causing deposits on the heater element that wouldn't burn off properly during normal operation. This is not a critical code unless the rear O2 is downstream of the last catalyst.

Related codes

  • P0143 – Sensor 1 Oxygen Circuit Low Voltage (Bank 1 Sensor 2)
  • P0144 – Sensor 2 Oxygen Circuit Low Voltage (Bank 1 Sensor 3)
  • P0325 – Crankshaft Position Sensor A Circuit Malfunction
  • P0335 – Crankshaft Position Sensor A Circuit Range/Performance Problem
  • C1274-Power steering pressure sensor circuit range/performance problem. 

How much does it cost to fix the P0142 code?

Typically, it is expensive to fix the P0142 trouble code. Most companies charge $150-$500 for replacing an O2 sensor. The average car has 3-4 oxygen sensors (O2 sensors). Replacing all of them would cost over $1,000. However, some technicians can do this work for as low as $50-$100 per O2 sensor replaced. This depends on where you live and your location.

Conclusion

P0142 is a sensor 3 circuit problem or an open/short in the heated oxygen sensor circuit in bank 1. The Check Engine Light comes on when this code appears and it means that there's a problem with the heated element circuit in an O2 sensor somewhere downstream of the catalytic converter. It could have failed due to excessive heat due to misfire, but it could also have failed because of poor fuel quality causing deposits on the heater element that wouldn't burn off properly during normal operation. This code isn't critical unless the rear O2 is downstream of the last catalyst.

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