Fault code P0146 – O2 sensor circuit no activity detected (Bank 1, Sensor 3)

Fault code P0146 is called “O2 Sensor Circuit No Activity Detected (Bank 1, Sensor 3)” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0146

This Diagnostic Trouble Code (DTC) is a generic powertrain code. Error P0146 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P0146 – O2 sensor circuit no activity detected (Bank 1, Sensor 3)

The Powertrain Control Module (PCM) provides an initial voltage of 0.45 V to the oxygen sensor. When the O₂ sensor reaches operating temperature, it generates a voltage that varies depending on the oxygen content of the exhaust. Poor exhaust generates a low voltage (less than 0.45 V), and rich exhaust generates a high voltage (more than 0.45 V).

O₂ sensors on a particular unit are used to monitor the emissions, this sensor has #3. A three-component catalyst (TWC) system (catalytic converter) is used to control the exhaust.

The PCM uses the signal received from oxygen sensor 3 (#3 indicates the sensor after the catalytic converter, the sensor before the catalyst has #1) to determine TWC efficiency.

Normally, this sensor will switch between high and low voltage noticeably slower than the front sensor. This is normal. If the signal received from the rear (#3) O₂ sensor indicates that the voltage is “stuck” between 0.425V and 0.474V. PCM determines that this sensor is inactive, and code P0146 will be set.

Symptoms of vehicle malfunctions

The main signal that an error P0146 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The Check Engine Indicator Light (CEL) or the Malfunction Indicator Light (MIL) will come on.
  2. High fuel consumption is possible.
  3. Too much smoke is coming out of the exhaust pipe.
  4. Most likely, there will be no other noticeable problems other than “Check engine” on the control panel.

The reason is this: the oxygen sensor behind or after the catalytic converter does not affect the fuel supply. It only measures the efficiency of the catalytic converter. For this reason, you most likely will not notice any problems with the engine, with the P0146 malfunction.

Factors that can cause this error code

The error code P0146 can mean that one or more of the following problems have occurred:

  • The heater circuit of the oxygen O₂ sensor may be short-circuited. (Usually requires replacement of the heater circuit fuse also in the fuse box.)
  • The signal circuit in the oxygen sensor O₂ is shorted.
  • Melting of harness connector or wiring harness due to contact with exhaust system.
  • Water entering the harness connector or PCM connector.
  • Engine-ECU may be damaged.

How to fix or reset OBD-2 code P0146

Some suggested steps for troubleshooting and fix the error code P0146:

  1. With the car warmed up, use the OBD scanner to check the oxygen sensor voltage (it should change periodically).
  2. Check 12 volt circuit coming to the sensor, if there is a problem, fix it.
  3. Diagnose the 5 volt circuit from the control unit to the sensor, correct the problem if necessary.
  4. If the above mentioned problems are not confirmed, replace the oxygen sensor O₂ bank 1, sensor 3.

Diagnose and repair of problems

This is a rather specific problem P0146 and should not be too difficult to diagnose.

First start the engine and warm it up. Use the diagnostic tool to monitor the voltage of the sensor O₂ unit 1, sensor 3. Normally the voltage should switch slowly above and below 0.45 volts.

If this is the case, the problem is probably temporary. You will have to wait until the problem is detected before you can accurately diagnose it. However, if it doesn’t switch or hangs up, do the following.

Turn off the vehicle. Visually inspect the connector and wiring harness block 1, sensor 3 for melting or fraying. Repair or replace if necessary.

Turn on ignition, but turn off engine. Disconnect sensor connector O₂ and check for 12 V. In heater power supply circuit and proper grounding. If there is no 12 V heater power supply, check for faulty open circuit fuses.

If the heater circuit fuse blows, it can be assumed that a faulty heater in the sensor O₂ is causing the burnout. Replace the sensor and fuse, then retest. If grounding is missing, check the circuit and clean or repair the grounding circuit.

Next, on the disconnected connector, check for a 5 volt signal coming from the control box. If it is not present, check for 5 volts on the PCM connector. If 5 volts are present at the PCM connector, but not at the O₂ connector of the sensor wiring harness. Then there is a break or short in the wire between the PCM and the O₂ connector of the sensor harness.

If there is no 5 volts on the PCM connector, most likely the PCM unit is faulty due to an internal short circuit. In this situation it is necessary to replace the PCM.

If all voltages are present, it is necessary to replace the oxygen sensor O₂ Bank 1, Sensor 3. After that, reset the error and recheck with the scan tool, the error P0146 should disappear.

On which vehicles does this problem occur most frequently

Fault code P0146 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Cadillac
  • Chevrolet (Blazer, Silverado)
  • Ford
  • GMC (Safari)
  • Jeep
  • Mitsubishi
  • Nissan (Altima, Rogue)
  • Opel
  • Toyota
  • Volkswagen (Passat)

Fault code P0146 can sometimes be found with other errors. The most common are the following: P0043, P0130, P0134, P0135, P0141.

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