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Yet another chime in Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Tue, 25 Oct 2005 09:30:45
In Reply to: O2 follow up questions for Anders , Ari , John B & all, John Daikh, Tue, 25 Oct 2005 00:33:24 Members do not see ads below this line. - Help Keep This Site Online - Signup |
A voltmeter set to volts won't damage the O2 sensor, as the others have said. Reading volts is a relatively passive thing. The meter does consume a small amount of current from the sensor. The O2 sensor produces a voltage, and very little current. A typical digital voltmeter takes minimal current from the sensor. A good analog meter pulls very little current. A very cheap analog meter may pull enough current from the sensor to affect the voltage it puts out. This won't damage either the O2 sensor or the ECU.
Ohms is entirely the wrong way to measure an O2 sensor. It will look like an open circuit to an ohm meter, sensor good or not. And yes, an ohm meter does it job by putting a voltage across the load, and measuring the current. Measuring Ohms with most ohm meters won't damage an O2 sensor. Now, if you have a specialty meter designed to measure very low resistances (like 0.01 ohms) for specialized electrical bonding, yes, those can put out 250 or 500 volts. But those are very special, very expensive, and you'd know it if you have one.
Can measuring resistance damage the ECU if it's connected? Theoretically yes, practically - probably not. The underhood environment is nasty from an electrical standpoint - large currents from the alternator and starter, high voltages from the spark plugs, and yes, cars do live in a lightning environment. So most electrical inputs to the ECU have some protection on them. For a high impedance signal like the O2 sensor, there is most likely a series protection resistor. That said, it doesn't hurt to be safe.
So, how do you read the output of the O2 sensor? Depends. A decent digital voltmeter will work - you can't set the output exactly, but you can get close. Some nicer DVMs have a little analog bar graph on the bottom - that works great. An oscilloscope is great, but most folks don't have one. Even a $30 analog meter should do a decent job.
There are two kinds of bad O2 sensors. One is stuck at 0.2 or 0.9 volts. That's bad, assuming it's not a mixture problem. You can tell that easily with a meter. The other kind of bad is a 'slow' O2 sensor, where it responds, but just slowly. You can't tell anything is wrong with a meter - the output swings back and forth just like a good one. The only way to fix that is to replace the sensor.
posted by 192.249....
, Tue, 25 Oct 2005 09:30:45 <-- Viewing This Message
, Tue, 25 Oct 2005 06:52:31
, Tue, 25 Oct 2005 08:05:33, Tue, 25 Oct 2005 09:53:51, Tue, 25 Oct 2005 12:18:05
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