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I have a 1991 Ford Escort that I suspect is running rich so today I probed the 2 upstream Lambda sensor signal wires with my Vantage Pro and found between 1.14-1.20 volts on the signal wires. Is it possible for narrow band o2 sensors to produce a 'high' voltage like this, I always thought 900mv was around the limit of rich? The voltage does not change from first startup to running up to temp.
The following user(s) said Thank You: Andy.MacFadyen
This type of O2 sensors shows this voltage when they are shorted to positive . Even when you short it to 12 V it woon't show more due to the way how the ecm processes the information.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
The following user(s) said Thank You: Andy.MacFadyen, jeoff82
A general rule of thumb for any feedback device is that any values outside a normal range indicates an open/short circuit.
Think of a 5v reference circuit. A map sensor. Operating range might be 0.5v to 4.5v. why not 0v or 5v? Those values are reserved for circuit testing by the ECM.0v might indicate a short and 5v might indicate an open, the ECM then sets the DTC. Not always, sometimes they're dumb. But, if you see an oxygen sensor with values outside of normal range, expect a circuit problem.
The following user(s) said Thank You: Noah, jeoff82
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