P0140 Lack of activity in the oxygen sensor circuit (B2S1)

OBD-II Trouble Code - P0140 - Data Sheet

• P0140 Lack of activity in the oxygen sensor circuit (B2S1)
• No activity in the sensor circuit (block 1, sensor 2)

What does DTC P0140 mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Although general, specific repair steps may differ depending on the brand / model.

The powertrain control module (PCM) supplies a 45 V reference to the oxygen sensor. When the O2 sensor reaches operating temperature, it generates a voltage that will vary depending on the oxygen content of the exhaust gases. Lean exhaust generates low voltage (less than 45 V), while rich exhaust generates high voltage (more than 45 V).

O2 sensors on a specific bank, labeled as “sensor 2” (like this one), are used to monitor emissions. A three way catalyst (TWC) system (catalytic converter) is used to control the exhaust gases. The PCM uses the signal received from the oxygen sensor 2 (# 2 indicates the back of the catalytic converter, # 1 indicates the pre-converter) to determine TWC efficiency. Typically this sensor will switch between high and low voltage noticeably more slowly than the front sensor. This is fine. If the signal received from the rear (# 2) O2 sensor indicates that the voltage is stuck in the range of 425 V to 474 V, the PCM detects that the sensor is inactive and sets this code.

Possible symptoms

The Check Engine Light (CEL) or Malfunction Indicator Light (MIL) will illuminate. There will likely not be any noticeable handling issues other than the MIL. The reason is this: the oxygen sensor behind or after the catalytic converter does not affect the fuel supply (this is an exception for Chrysler). It only MONITORS the efficiency of the catalytic converter. For this reason, you most likely will not notice any engine problems.

• An indicator lights up indicating a problem.
• Rough engine work
• Indecisiveness (when accelerating after deceleration phase)
• The ECM loses its ability to maintain the correct air/fuel ratio in the fuel system (this can cause erratic driving symptoms).

Causes of the P0140 code

The reasons for the appearance of the P0140 code are quite few. They can be any of the following:

• Short circuit in the heater circuit in the O2 sensor. (Usually requires replacement of the heater circuit fuse also in the fuse box)
• Short circuit in the signal circuit in the O2 sensor
• Melting of the harness connector or wiring due to contact with the exhaust system
• Water ingress into the wiring harness connector or PCM connector
• Bad PCM

Possible solutions

This is a fairly specific problem and shouldn't be too difficult to diagnose.

Start the engine first and warm it up. With a scan tool, observe the Bank 1, Sensor 2, O2 Sensor Voltages. Typically, the voltage should switch slowly above and below 45 volts. If so, the problem is most likely temporary. You will have to wait until the problem is found before you can diagnose it accurately.

However, if it does not shift or gets stuck, follow these steps: 2. Stop the vehicle. Visually inspect the Bank1,2 harness connector for melting or abrasion in the harness or connector. Repair or replace as necessary 3. Switch on the ignition, but switch off the engine. Disconnect the O2 sensor connector and check for 12 volts on the heater power circuit and proper grounding on the heater circuit ground circuit. but. If no 12V heater power is available, check for correct open circuit fuses. If the heater circuit fuse is blown, it can be assumed that the defective heater in the o2 sensor is causing the heater circuit fuse to blow. Replace sensor and fuse and recheck. b. If there is no ground, trace the circuit and clean or repair the ground circuit. 4. Then, without plugging in the connector, check for 5V on the reference circuit. If not, check for 5V on the PCM connector. If 5V is present at the PCM connector but not at the o2 sensor harness connector, there is an open or short in the reference wire between the PCM and the o2 sensor connector. However, if there is no 5 volts on the PCM connector, the PCM is probably faulty due to an internal short circuit. Replace PCM. ** (NOTE: On Chrysler models, a common problem is that the 5V reference circuit can be short-circuited by any sensor in the vehicle that uses a 5V reference signal. Simply turn off each sensor one at a time until 5V reappears. The sensor you disconnected is a shorted sensor, replacing it should clear the 5V reference short circuit.) 5. If all voltages and grounds are present, replace the O1,2 sensor at Unit 2 and repeat the test.

HOW DOES A MECHANIC DIAGNOSTIC CODE P0140?

• Scans codes and documents, captures frame data
• Monitors O2 sensor data to see if the voltage is moving above or below 410-490mV.
• Monitors MAF sensor data to respond to throttle changes according to specifications.
• Follows manufacturer specific spot tests to further diagnose code (tests vary between manufacturers)

COMMON ERRORS WHEN DIAGNOSING CODE P0140?

• Before replacing the O2 sensor, check the mass air flow sensor for damage and contamination.

The lack of response of the O2 sensor can be caused by contamination of the mass air flow sensor and not calculating the amount of air entering the engine on the intake side.

HOW SERIOUS CODE P0140 IS?

• This code may be related to problems with the mass air flow sensor, which is necessary to correctly calculate the amount of air entering the engine. Along with the O2 sensors, failure of any of these components will cause the ECM to miscalculate the air/fuel ratio to the engine.
• The ECM may lose control or receive incorrect data from sensors such as the mass air flow sensor or O2 sensor if they are within specifications but incorrect.

These problems can lead to intermittent driving discomfort that can compromise driver safety.

WHAT REPAIRS CAN FIX CODE P0140?

After scanning and clearing all error codes and verifying the error:

• Check the O2 sensor to see if it changes as the fuel mixture gets richer.
• Check the mass air flow sensor for correct readings in accordance with the specification
• Replace the O2 sensor if it is dirty or fails the test.
• Replace the mass air flow sensor if it is dirty or fails the test.
• Clean the mass air flow sensor to see if the reading has changed.

ADDITIONAL COMMENTS REGARDING CODE P0140 CONSIDERATION

Lack of response from the O2 sensor could be due to contamination of the MAF sensor with things like oil from an oil-soaked air filter, like all sensors. This oil coats the sensor and can cause it to become inaccurate. Cleaning the sensor may solve the problem.

P0140 ✅ SYMPTOMS AND CORRECT SOLUTION ✅ - OBD2 Fault Code

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