Automotive Technology Course | O2 or Oxygen Sensor Testing, (incl. Heater)

Automotive Technology Course | O2 or Oxygen Sensor Testing, (incl. Heater)


Oh you you you the o2 sensor heater is in charge of keeping the oxygen sensor at proper operating temperature this is usually in excess of 600 degrees the two white wires are labeled heater plus and minus and they tend to be either white or black the black wire is the o2 sensor signal circuit and should not be confused with the o2 sensor ground the gray wire is the actual o2 sensor ground this ground is regulated and provided by the ECM one side of the o2 sensor circuit can be activated directly by the ECM as we see on this diagram or it could also be triggered through a relay bbcn may also trigger or turn on the o2 sensor heater circuit either positively or negatively depending on the manufacturer the o2 sensor circuit can also be pulsed triggered or simply left at a steady on stage always make sure and study the particular system that you are working on in some cases the ECM may completely urn the o2 sensor circuit off in the event of an impending o2 sensor heat or circuit problem the first step in any o2 sensor heater test procedure is to scan the ECM for any o2 sensor heater codes this is usually the first indication that you’ll ever have a banner to sensor heater problem start by identifying the o2 sensor wires the two white or black o2 sensor wires normally belong to the heater circuit the other two wires are the oxygen sensor signal and ground circuit wires you should always consult two wiring diagram for o2 sensor wiring identification the only two pieces of equipment that you’ll ever need during an o2 sensor heater test are the test light and the digital multimeter to avoid going on the wrong diagnostic path make sure that your test light is fully operational step number two is to verify for proper o2 sensor heat or power feed in our test vehicle the power feed comes from the fuse box and not the ECM the test light should immediately light up and verify proper o2 sensor heat or power feed and the important step in knows whose sensor heater testing is to find out if the ECM provides the power for a ground depending on the circuit design this may be done via relay or through the actual computer since both o2 sensor heater circuit wires are of the same color any one of them could be the power feed wire so test both of these wires respectively step3 proceeded to test the o2 sensor heater ground wire change the digital multimeter lead from chassis or battery ground to battery positive in our test vehicle this ground is provided by the ECM this o2 sensor heater line could also be energized by a relay on early model vehicles an important factor to remember during all OH – sensor heater tests is to erase any and bending codes these and bending coats may prevent the ECM from turning this circuit home and sending you in the wrong diagnostic path thinking that there is a problem with the actual wiring the ECM does this to simply protect itself against any short-circuit present if this code is not erased the o2 sensor heater circuit will always be an active and you may also suspect a faulty ECM which is really not the case after the o2 sensor heater coats have been erased turn the engine on and allow the ECM to turn the o2 heater circuit on in most modern systems the ACM may not act evade the o2 sensor heater circuit if the engine is off a non-operational heater circuit points to a faulty ECM just make sure that all the previous conditions are met before you actually condemn the ECM the last step in o2 sensor heater testing is to perform an actual heater continuity test start by disconnecting the o2 sensor connector and connecting the digital multimeter across to o2 sensor heater wires before that touch the two multimeter leads to verify that the meter is actually working then take an actual resistance reading of the o2 sensor heater but good o2 sensor heater should have between 50 and 90 ohms when reading a nose who sends her signal cycle a complete cycle is the time it takes this signal path to cross the same point on the oscilloscope or graphing multimeter screen as in these two points marked by the arrows by measuring the time that takes for the signal to cross these two points and dividing one by the time the frequency of the o2 sensor can be deduced just remember that any two same points along the signal path will work just fine a desired feature of a digital multimeter or oscilloscope are the measuring cursors by simply placing the o2 sensor signal between these two cursors the exact cycle time can be measured this waveform capture and measurement principle can also be used to test many automotive sensors and actuators a simple 4 wire lose sensor is composed of the heater plus and minus the o2 sensor ground and vo2 sensor signal the o2 sensor may be grounded at its body or by a ground provided by the ECM a loss of the o2 sensor ground provided by the ECM will also render the o2 sensor useless always check for proper o2 sensor ground at the ACM ground circuit wire or at the dedicated ground splice usually bolted to the engine block step 1 in electric low to sensor testing is to connect wire tap to the o2 sensor signal wire which is where all of then connect the digital mod 2 meter black lead to a suitable chassis ground or to battery negative do not mistake the o2 sensor ground wire for the signal wire the ground wire is usually gray and the signal wire is normally black set you multimeter or oscilloscope for a maximum range of 1 volts remember although 2 sensors generate a voltage between 0 and 1 volts this of course is the theoretical range in order for the ECM to be in full control of the mixture the o2 sensor should always be cycling if the o2 sensor is not cycling then the ECM is an open loop and therefore not in control of the air fuel mixture in our test vehicle the ECM is not an air fuel control due to an impending o2 sensor heater code a race although to sensor related codes before testing the o2 sensor response then goose the throttle and test the o2 sensor lean and rich response respectively the o2 sensors should reach at least 150 millivolts on the one side and 800 millivolts on the rich side since this vehicle had and l2 sensor heater fault the o2 was replaced and the memory was erased after the memory was erased the system immediately went into closed-loop indicating that the ECM was in full air fuel control step number three verify for proper o2 sensor cycling frequency a minimum of one Hertz or one cycle per second as he did in this step simply freeze the waveform and use the cursors to measure the time it takes for the o2 sensor signal to complete one cycle then divide one by this time period to get the frequency by using this method the need for a complicated o2 sensor response test is avoided making for a fast testing procedure in this waveform close-up we can see the cursors being placed to measure a complete total sensor cycle remember you can always place the cursors on any two same points in the waveform including the upper or lower crests in this example we can see the two cursors intersecting two same points along the waveform in this case the two positive o2 sensors sacral humps or crests in the lower-right on the screen we can see that the o2 sensor took point five five seconds to complete one cycle this is well below the one second time limit by simply dividing one by the time in this case point five five seconds a frequency of one point eight Hertz is deduced this is well within proper range remember a frequency equals or faster than one Hertz is needed for the ACM not to flag the o2 sensor as faulty following is the same procedure but with a faster sweep time by raising the sweep time we can capture the o2 sensor signal and better detail remember the o2 sensor response test simply entails an analysis of the o2 sensor frequency and amplitude this is exactly the same criteria that the ECM uses to test the o2 sensor you you


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