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Message: <blockquote data-quote="drexchan" data-source="post: 668126" data-attributes="member: 6936">Let's start with some basic on how Oxygen Sensor works in the EFi system.An http://drexchan.fotopic.net/p16912724.html generates a voltage output within the 0V to 1V range when fully warmed up to the operating teperature, 315°C and above. The voltage generated depends on the amount of oxygen in the exhaust stream and accurate reading can only be achieved when it's warmed up to the operating temperature.The input from the O2 sensor is used by the ECU to keep the air/fuel ratio as stoiciometric (14.7) as possible. That means that for every gram of petrol the engine burns, it will need 14.7 grams of air, or 3.1g of oxygen.This is commonly known as the O2 feedback system and when this system is operating it is said to be in "closed loop". When it is not operating, meaning the computer is not reading and responding to the oxygen sensor, it is said to be in "open loop".All O2 sensors are vented to the atmosphere which contains approximately 21% oxygen. The exhaust of a ideally-tuned petrol-powered engine typically contains 2% oxygen, max.Lean: If the exhaust has > 2% oxygen, it is lean (A/F ratio > 14.7). This produces a low voltage of < 0.3V.Rich: If the exhaust has near 0% oxygen, it is rich (A/F ratio < 14.7). This produces a high voltage of > 0.6V.The voltage signals are sent to the ECU and it reacts by adjusting the air/fuel ratio. The signal output is therefore fluctuating around 0.45V in a sinus pattern. Each cycle take less than 0.3 sec for a healthy, sensitive sensor.In order to read the O2 sensor, most ECU send out a certain voltage to the output terminal of the sensor. This is typically around 0.45V. Since we know that the sensor sends low voltage (< 0.3V) when a lean condition is present and a high voltage (> 0.6V) when a rich condition is present, the computer can count the number of times the sensor crosses the 0.45V mark. Cross-counts are the number of times an O2 sensor crosses 0.45V. A scanner such as PDT2000 can read this.The ECU can only use the sensor's output information under certain conditions.A] the sensor must be hot to produce a normal signal (> 315°C).This is why most sensors today have built-in heaters to counteract the cooling effects of prolonged idling and to achieve closed loop mode sooner during warm-up. Heating the sensor also keeps it cleaner and extends its life considerably. The heater usually gets voltage from a constant "key-on" source like the fuel pump relay or a fuse. For the Proton models (such as Wira with S-VDO ECU) are now using a http://drexchan.fotopic.net/p16912727.html, from NTK, Japan. The four wires are:1. O2 sensor output (black)2. O2 sensor ground (gray)3. 12V heater feed (white)4. 12V heater ground (white).B] The ECU is programmed not to go into closed loop operation until the coolant temperature sensor tells the computer the engine is warmed up. If the system tries to go into closed loop too early in the warm-up period, the leaning effect of the system would cause driveability problems and pollutants.C] The ECU is also programmed to ignore the O2 sensor at near wide open throttle conditions. Maximum power requires maximum enrichment.We can then conclude that O2 sensor feedback is used when the engine is warmed up, at Idle, and at part throttle (cruise) conditions.</blockquote>

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