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
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?
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This article originally appeared on YourMechanic.com as P0143 OBD-II Trouble Code: O2 Sensor Circuit Low voltage (Bank 1, Sensor 3) and was authored by Jay Safford.