P0143 OBD-II Trouble Code: O2 Sensor Circuit Low voltage (Bank 1, Sensor 3)

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P0143 is a diagnostic trouble code (DTC) for "O2 Sensor Circuit Low voltage (Bank 1, Sensor 3)". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

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Diagnostic Trouble Code (DTC): P0143

P0143 code definition

O2 Sensor Circuit Low voltage (Bank 1 Sensor 3)

What the P0143 code means

P0143 is the OBD-II generic code indicating that the Engine Control Module (ECM) input from the O2 sensor circuit for bank 1 sensor 3 has a low voltage.

What causes the P0143 code?

  • The O2 sensor bank 1 sensor 3 is downstream of the last catalyst in the exhaust system, so an exhaust leak before the sensor can cause the code due to excessive oxygen getting into the exhaust stream. This could cause the sensor voltage to be lower than expected.

  • The ECM detects a low voltage in the O2 bank 1 sensor 3 circuit. This can be caused by a shorted or open circuit of the sensor wire to the ECM.

What are the symptoms of the P0143 code?

  • The ECM does not use the input from this O2 sensor for controlling the engine fuel control, so it should not account for any abnormal drive complaints.

  • The Check Engine Light will be illuminated indicating a problem with the downstream catalyst O2 sensor 3 for bank 1 of the engine.

How does a mechanic diagnose the P0143 code?

  • Checks electrical connections to the O2 bank 1 sensor 3 for shorts or open circuits

  • Checks the exhaust system before the O2 sensor for any exhaust leaks causing excessive oxygen to cause the sensor to input excessive oxygen in the exhaust

  • Scans to see if code P0143 can be cleared and does not return. Monitors the O2 sensor for voltage readings to go above .2 volts

  • Follows the manufacturer's specific pinpoint tests for further diagnosis

Common mistakes when diagnosing the P0143 code?

Follow these simple guidelines to prevent misdiagnosis of code:

  • Clear the codes and verify sensor failure by retesting and road testing under the same conditions of the original failure (found in the freeze frame data).

  • Check for any exhaust leaks or damages to the exhaust manifold or header pipes before the O2 sensor that will cause the sensor to not work correctly.

How serious is the P0143 code?

  • This code is for the sensor behind the last catalyst on bank 1 of the exhaust system inputting a low voltage to the ECM and may contribute to excessive exhaust emission.

  • The code will not cause the engine to run any different in most circumstances since the ECM does not use it for fuel control.

  • The vehicle will fail emission testing if the Check Engine Light does not clear.

  • The exhaust may have a leak and cause exhaust fumes to get into the passenger compartment.

What repairs can fix the P0143 code?

  • Repairing the exhaust leaks before the catalyst. The excessive oxygen getting into the exhaust can cause the O2 sensor to read low voltage.

  • Repairing or replacing the wiring or connection to the O2 sensor for bank 1 sensor 3

  • Replacing the O2 sensor

Additional comments for consideration regarding the P0143 code

The code P0143 will not cause a driveability problem since this O2 sensor is not used for fuel control and is only used to monitor the catalyst efficiency.

Need help with a P0143 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

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