O2 sensor voltage troubleshooting
10-31-2002, 03:46 PM
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O2 sensor voltage troubleshooting
After hooking up my Autometer A/F gauge, I decided to do some voltage readings from the O2 sensor to see if I was getting any deviant outputs from it (O2 sensor is old and hence the test).
Anyway, here are my results. This is on a stock 951 (mods are not on the car yet). The car was warmed up.
Disconnect O2 sensor at firewall and put multimeter (+) lead to the O2's black wire (signal wire) and (-) lead to battery ground. I got readings from .810 to .850. This appears to be normal as the disconnected O2 sensor will cause the engine to run rich. I will call this the baseline reading.
Funny thing is that if I throttle up sleadily, the O2 sensor drops to about .780. Isn't it supposed to go higher than the baseline?
I also wanted to check for proper grounding to the A/F gauge. I inserted the (+) lead into the DME harness side of the O2 connector. The lead fits in perfectly. Then, I took the (-) to the battery ground. Car was idling and I got a reading of .435. Now, isn't the DME side to just read nothing at all?
I went to the A/F signal line and hooked up my multimeter there. Same exact reading as the O2 sensor connector (.435). At least I'm getting the same voltage reading on the O2 connector and at A/F gauge end.
How come I'm getting a voltage reading at the DME when there's no O2 sensor hooked up?
Is the DME doing something I don't know about?
Anyway, here are my results. This is on a stock 951 (mods are not on the car yet). The car was warmed up.
Disconnect O2 sensor at firewall and put multimeter (+) lead to the O2's black wire (signal wire) and (-) lead to battery ground. I got readings from .810 to .850. This appears to be normal as the disconnected O2 sensor will cause the engine to run rich. I will call this the baseline reading.
Funny thing is that if I throttle up sleadily, the O2 sensor drops to about .780. Isn't it supposed to go higher than the baseline?
I also wanted to check for proper grounding to the A/F gauge. I inserted the (+) lead into the DME harness side of the O2 connector. The lead fits in perfectly. Then, I took the (-) to the battery ground. Car was idling and I got a reading of .435. Now, isn't the DME side to just read nothing at all?
I went to the A/F signal line and hooked up my multimeter there. Same exact reading as the O2 sensor connector (.435). At least I'm getting the same voltage reading on the O2 connector and at A/F gauge end.
How come I'm getting a voltage reading at the DME when there's no O2 sensor hooked up?
Is the DME doing something I don't know about?
11-05-2002, 04:09 PM
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Your results sound OK.
With the O2 sensor you're running rich. The DME creates the .45V with the O2 sensor disconnected.
Now take 2-3 strands of wire out of a 2" length of 10 or 12 gauge wire, you should be able to twist them together & put them into the socket in the O2 connector for the black wire & then reconnect the DME side of the connector. This way the DME still gets the O2 sensor signal & you can monitor the results.
Connect your voltmeter between these strands & a ground. When you start up your signal will rise from .45 to about .8V & once the the system starts to get hot (5 minutes) you should see the signal osscillate between .1 & .9 volts every 1 or 2 seconds.
If it doesn't then your sensor is dead or your DME is not functioning correctly.
With the O2 sensor you're running rich. The DME creates the .45V with the O2 sensor disconnected.
Now take 2-3 strands of wire out of a 2" length of 10 or 12 gauge wire, you should be able to twist them together & put them into the socket in the O2 connector for the black wire & then reconnect the DME side of the connector. This way the DME still gets the O2 sensor signal & you can monitor the results.
Connect your voltmeter between these strands & a ground. When you start up your signal will rise from .45 to about .8V & once the the system starts to get hot (5 minutes) you should see the signal osscillate between .1 & .9 volts every 1 or 2 seconds.
If it doesn't then your sensor is dead or your DME is not functioning correctly.
