Weekly Waveform 21 - Testing Oxygen Sensor Signal and Heater Circuits

In the automotive weekly waveform #21 I will show you how to scope a narrow band O2 sensor circuit. I will be scoping the rear O2 sensor signal and heater circuit on my 2004 Chevrolet express van with a 5.3.
The heater circuit on this van gets power anytime the key is on and the computer controls the ground circuit. If the heater doesn't work properly the oxygen sensor will take a long time to warm up and the tailpipe emissions will be higher.
The signal circuit will fluctuate between 0.1 volt and 0.9 volt on a good sensor. If checking a front O2 sensor the signal will switch from high to low at least once per second. The rear O2 will have a much slower switch interval if the vehicle has a good catalytic convertor. Many rear O2 sensor will hover between 650mv and 850mv most of the time if the convertor is good.
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[@KC-vp7wn]

So my blazer was giving me a P0147 code and when I looked at the signal I saw only the bias voltage of the O2 sensor. I only saw the heater voltage when I first turned the key on and the voltage what only there for about 5 seconds. I didn’t have an amp clamp that small to check the current draw. I did check the ohms of the heater element and it read a direct short. I figured I’d see some low amount of ohms.
So I replaced the O2 sensor and now I do see the switching of the heater voltage and a normal switching of the sensor signal. Glad I saw your video!
An electronics tech by trade but a home car mechanic to save myself money! 👍🏻

[@timothymohammed919]

you all deserve more likes and subscribers ......

[@7minnow]

Great Job

[@8power0]

LOVE THESE CLASSES I DO NOT TRY MISSING THEM THANKS SO MUCH . IS THERE A AVERAGE AMPERAGE READING FOR A O2 SENSOR SO I COULD KNOW IT'S ACTUALLY WORKING OR AT LEAST DOING SOMETHING. THANKS AGAIN FOR YOUR TIME AND EFFORT !!!!!!!!!!!!!!!!!

[@ThePracticalMechanic]

Most heater circuits will pull around 1 amp. Some vehicles will be less than that when the computer changes duty cycle of the heater ground. The amperage on the signal wire will be very small so we typically just check the voltage on that circuit. The signal will range between 0.1v and 0.9 v for most vehicles and 1.5v to 2.5v on some Chrysler products.

[@weldingjunkie]

Excellent video Chad this is great stuff. If you ever want to do nvh videos I can send my kit to you so you can do some on that.

[@bernardaflores1720]

Can you make a video regarding the strategy that is used to determine a good working sensor. I been told that Honda uses the rear sensor to determine weather the AFR or up stream sensor is working. You get a code for the front and not the rear sensor.

[@smms5056]

Awesome 👍 very good teacher

[@mechtechmechanical1571]

great vid good explanation

[@jimwhite5964]

Great job... thanks!

[@Trippy_Hippy89]

So if the cat converter was working would the ecu read a steady 450 millivolt signal from the rear 02 sensor.

[@ThePracticalMechanic]

Typically you’ll see 650 to 750 mV that is fairly steady if the catalytic converter is working and everything is warmed up. If the signal is stuck at 450 mV the O2 sensor may not be warming up properly or you have an open circuit on the signal wire.