Mechanical Problems & Technical Chat - o2 sensor reading question

Hello again,

I just ran anO2 sensor test on my '95 Civic with a D15B7 engine. It got into closed loop quite quickly (within no more than one minute), but the reading onthe (nondigital) voltmeter was .1 to .6 or .7 rather than .1 to .9 as suggested in the repair manula and other references on the internet. The scale was Dc 3. I'm wondering if the reading that I got is indicative of a functioning or a nonfunctioning 02 sensor.

The other thing is that when I used an Ohm meter to test the O2 sensor heater between the C and D terminals, the meter just dropped down to 0, rather than register a reading (Haynes suggests a reading of 10 to 40 is desirable). I believe that I'm running this test correctly. Is 0 the usual reading for a malfunctioning heater component on the sensor? And would that also lower the above reading from .9 to .6 or so? This is a bit technical, so I appreciate any help from those experienced with O2 sensors. Thanks,

Andy

Based on the Ohm readings, I would think that the CEL turns ON and throws code 41. If so, then all the information would point to a fault in the heater circuit.

As for the possible low voltage reading from the O2 sensor itself, the answer depends on the accuracy of the voltmeter. Can the voltmeter be dialed to a lower range, such as 1 V, where the measurements would be more accurate?

You have to use a digital voltmeter, or a VTVM or FET-VOM (remember those?). An ordinary analog voltmeter will overload the output of the sensor and cause a false low reading. It's a very high impedance output. Also before you measure resistance with an ordinary analog voltmeter it needs to be zero'd first.

I did zero the voltmeter first, so I'm going to assume that the sensor is fine (according to your responses concerning getting a lower reading with the nondigitial kind). I do have another question concerning RonJ's post. I have been driving an '88 B2200 for about 10 years and the only kind of testing system that I am familiar with is the OBDII on my girlfriend's Jetta. Ron wrote "Based on the Ohm readings, I would think that the CEL turns ON and throws code 41." My check engine light is not on, but how does one go about checking for codes with these older cars?

Andy

To read the codes out of a '95 you jumper the 2-wire test plug near the ECU, turn the key on and count the blinks of the CEL. If the CEL comes on and stays on steady when you do this, that means there are no codes stored. To clear the codes, with key off, either disconnect the battery or remove the "BACK UP" fuse under the hood for 10 seconds. Either of these procedures will also erase the clock and settings in the radio.

I agree your sensor is fine. When you have no CEL and a non-zero varying voltage of any sort it is OK.

As you measured no resistance in the heater circuit, which should have yielded a 10-40 Ohm reading, I thought that the heater circuit might be bad. However, this idea is inconsistent with the fact that the CEL is OFF and no code 41 was thrown. Therefore, I think the O2 sensor heater circuit is fine, though I don't understand why you failed to measure any resistance on this circuit.

Here's how to pull CEL codes:

http://www.honda-tech.com/zerothread/1901557