It should be noted that the oxygen sensor is only capable of generating a signal voltage when warmed up to normal operating temperature (about 320°C). While the sensor is cold, the PCM operates in OPEN LOOP mode.
If, with the engine warmed up to normal operating temperature and / or running for at least two minutes, the oxygen sensor generates a stable signal with an amplitude below 0.45 V (at a speed of at least 1500 per minute), the self-diagnosis system stores the corresponding fault code in the PCM memory (P0131 or P0132). The corresponding code is also entered in the event of a malfunction in the sensor heater circuit (see Section On-Board Diagnostic System (OBD) - the principle of operation and fault codes).
In the event of a malfunction of the λ-probe or its circuit, the PCM switches to open-loop mode, ignoring the information coming from the sensors and maintaining the composition of the air-fuel mixture at a certain predetermined level, which ensures sufficient efficiency of the engine output.
The correct functioning of the oxygen sensor depends on the fulfillment of a combination of certain specific conditions:
- a) Electrical parameters: The stability of the low voltage amplitude signal generated by the sensor depends to a large extent on the quality of the contact connections of the λ-probe circuit, which should be checked first of all in case of problems;
- b) Outside air supply: The design of the λ-probe provides for the free circulation of outside air inside the sensor. When installing the probe, always check the patency of the air channels;
- c) Operating Temperature: The PCM only responds to information from the λ probe after the probe has warmed up to normal operating temperature (about 320°C). This fact should not be overlooked when checking the correct operation of the probe;
- d) Fuel quality: Proper functioning of the λ-probe becomes possible only if UNLEADED fuel is used for refueling the car!
In addition to the conditions listed in the previous paragraph, some special precautions must be observed when servicing the λ-probe:
- a) The oxygen sensor is equipped with a piece of electrical wiring permanently mounted in it and equipped with a contact plug, attempts to disconnect which can lead to irreversible failure of the sensor;
- b) Try to keep the sensor louvers or its electrical connector free of dirt and grease;
- c) Do not use any solvents to clean the oxygen sensor;
- d) Handle the λ-probe with extreme care, do not drop it and try not to shake it off;
- e) The silicone protective cover must be worn on the sensor in a strictly defined way so as not to be melted and not to impair the proper functioning of the probe.
Examination
1. Locate the sensor's electrical connector. From the reverse side of the connector, insert an unfolded paper clip into the signal wire contact socket (terminal no. 1 [+]), insert the second paper clip into the socket of terminal No. 2 (weight). Connect the positive probe of the voltmeter to the first paper clip, connect the negative probe to the paper clip inserted into the ground terminal. Set the parking brake, move the AT selector lever to the position "R", on models with manual transmission, select neutral. Jack up the front of the car and place it on jack stands.
2. Start the engine and begin to monitor changes in the oxygen sensor signal voltage.
Attention! try not to touch the heated surfaces of the exhaust system.
Slower voltage fluctuations of the secondary λ-probe are a consequence of the action of the catalytic converter, since the bound oxygen atoms in the CO2 and H2O molecules affect the sensitive element of the probe to a much lesser extent than the atoms in the CO and NOX molecules.
3. At the initial stage, the cold sensor must generate a constant signal with an amplitude of 0.1 ÷ 0.2 V (open loop mode). After about two minutes, the engine will reach normal operating temperature and the sensor reading will begin to fluctuate between 0.1 and 0.9 V (closed loop mode). If the system does not transition to closed loop mode, or transitions with an unacceptably long delay (lazy sensor), replace the λ probe.
4. Check up also serviceability of functioning of a heater of the oxygen gauge. Disconnect the probe wiring connector and connect an ohmmeter between the heater terminals (terminals No. 3 and 4). The nominal resistance is 10÷40 Ohm.
5. Check the power supply to the heater. Disconnect the electrical connector and measure the voltage on it from the side of the harness between terminal No. 4 and ground. With the ignition on (do not start the engine) The voltmeter should record the voltage of the battery. If there is no power, check the condition of the wiring on the circuit between the main relay, the PCM and the oxygen sensor.
6. If the above checks fail, replace the defective λ-probe.
Replacement
Note. Turning the λ-probe on a cold engine can be extremely difficult due to thermal compression of the metal of the exhaust manifold / exhaust pipe. To avoid the risk of damage to components, warm up the engine for a couple of minutes before removing the sensor - try not to burn yourself on heated surfaces during the procedure.
1. Disconnect the negative cable from the battery.
Attention! If the stereo system installed in the car is equipped with a security code, before disconnecting the battery, make sure that you have the correct combination to activate the audio system!
2. Jack up the car and put it on stands.
3. Carefully disconnect the oxygen sensor harness connector.
4. Carefully unscrew the probe from the exhaust manifold (primary sensor) or catalytic converter assembly (secondary sensor).
5. Before screwing the sensor into place, lubricate its threaded part with an anti-tack sealant (new sensors are usually already coated with the appropriate compound).
6. Screw the sensor into place and tighten it firmly.
7. Connect electrical wiring.
8. Lower the vehicle to the ground and test drive it. Check the control module memory for trouble codes.