Help with Oxygen or 02 Sensor testing + new wideband AFR sensor installation.

[Whiskey]

(Spoiler alert! O2 Sensor replaced + how to included in later post)

Ok, I am making a little plunge into learning how to do the testing and diagnostics for my car with a volt/ohm meter.

I have a volt meter and an OBDII monitor (DashDAQ) displaying a MIL code of P0135 (pre-cat 02 sensor heater circuit failure) I know that after the car has been run for more than 20 minutes, the short term fuel trim level goes back to zero, so that tells me that the heater circuit should be failing, but I want to know how to test this properly.

I selected Ohm on the volt meter and have the red and black leads connected on alligator clips to the number 4 and number 3 wire, both white, on the 02 sensor plug., respectively, and the reading is 2.46 M Ohm. I have no idea how to read this, and have spent about 10 hours looking for an answer through youtube and this site during the past week. I have looked at the wire diagram, but that gives wire colors back to the ecu and I don't know what I should look for there either.

What do I do to test the heater circuit?


2nd issue, but not as important. I have a wideband AFR sensor that I want to hook up to my DashDAQ. Can I install it just after the post-cat 02 sensor? There is easy access to the area once the rear driver-side tire is removed, and the heat-sheild is drilled out. Any suggestions would be appreciated.

[stinkyonion]

I would test the heater circuit by unscrewing the o2 sensor and then plugging the hole with a O2 sensor plug. You can get them online, i have bought a couple plugs (stainless and regular) for like $5 each. Start the car and see if the disconnected sensor gets hot. Or, just replace the sensor as it is a consumable and see if the alarm goes away.

[fpitas]

Originally Posted by Whiskey

Ok, I am making a little plunge into learning how to do the testing and diagnostics for my car with a volt/ohm meter.

I have a volt meter and an OBDII monitor (DashDAQ) displaying a MIL code of P0135 (pre-cat 02 sensor heater circuit failure) I know that after the car has been run for more than 20 minutes, the short term fuel trim level goes back to zero, so that tells me that the heater circuit should be failing, but I want to know how to test this properly.

I selected Ohm on the volt meter and have the red and black leads connected on alligator clips to the number 4 and number 3 wire, both white, on the 02 sensor plug., respectively, and the reading is 2.46 M Ohm. I have no idea how to read this, and have spent about 10 hours looking for an answer through youtube and this site during the past week. I have looked at the wire diagram, but that gives wire colors back to the ecu and I don't know what I should look for there either.

What do I do to test the heater circuit?


2nd issue, but not as important. I have a wideband AFR sensor that I want to hook up to my DashDAQ. Can I install it just after the post-cat 02 sensor? There is easy access to the area once the rear driver-side tire is removed, and the heat-sheild is drilled out. Any suggestions would be appreciated.

To my knowledge a wideband AFR sensor needs to be before the cat.

[stinkyonion]

Oh yeah. And to hook up the wideband, you take your car to the muffler shop with the rear clam off. Have then weld a o2 sensor bung onto catalytic converter. You can buy the bung etc. from zeitronix. And while your at it, can have them weld a exhaust gas temp probe bung to cylinder #3 header pipe. I love the dashdaq / zeitronix combo. The Dashdaq gps is a little small to read though, but I can live with it.

pictures clockwise: new o2 sensor bung on cat, egt probe sticking through header cover, bwr triple gauge with dashdaq (can only mount dashdaq to bottom position where sticks into foot area a little and not flush with guages), custom triple gauge (can only mount dashdaq to top position, is now flush with other gauges, way better but bad photo)

[Whiskey]

Good idea to take the 02 sensor out, put a fake plug in and test if the 02 sensor gets warm. But, I wanted to formally test the sensor in the engine bay before fighting the removal of the two under trays and removal of the 02 unit itself. I unplugged the sensor connectors, just under the wiper fluid, and am seeking a method, with an volt/ohm meter, to test the continuity of the heater circuit. Either the heater works or it doesn't, and I would like to know how to test this prior to extensive part removal.

Thanks for the idea.

[charliex]

the resistance will change based on the temperature of the sensor, it varies by sensor type and getting all the info on the sensors from the OEM's is about as easy as being a professional unicorn hunter, though finding the performance for that aspect of the sensor is easy enough.

a current check will tell you its heating up, how fast it heats up (if at all) determines if that code is set, and how much juice its drawing.

P0135 -> Set when the sensor output is greater than 1900mA or less than 250mA for 1.5 seconds, for 40 consecutive checks.

so its either not drawing enough, or too much.

[stinkyonion]

And here is one more photo of the wiring mess to install new head unit, amp, gauges, dashdaq, zeitronix, satellite radio, gps (took about 20 hours):

[Whiskey]

awesome.. nice setup. I like the photos.. Where is the AFR sensor, pre or post cat? Checked the zeitronix website and it should be pre-cat but the view on your pics looks post.

CharlieX: Why can't the heater circuit be tested?

[charliex]

its can, but it'd be easier to measure the mA draw of the heater, since that is what the ecu is looking at. <250mA probably open circuit or dead > 1900mA probably shorted or failed.

[stinkyonion]

wideband o2 sensor is precat for sure. The header would be on the bottome left of photo and the ubend off the right of photo. Picture taken from above.

[Whiskey]

I changed the oxygen sensor with a factory replacement this after noon. I know, I may have over paid, $103, but I was near the dealer on a Saturday around 6:00 PM and they had one left in stock and I wanted this thing fixed this weekend and have the exact part. Some parts are worth more in hand.

Installation was alright with the right tools. See pics below for the tools suggested/needed.

Short short version...
1. Remove Diffuser
2. Disconnect O2 sensor plug from ECU plug.
3. Unclip O2 wire from frame clip
4. Unscrew O2 Sensor
Reverse ..reverse

Detailed Version...
First remove the under tray. 8mm and 13mm socket will be needed. Remove the large 13mm bolts 1st with a socket wrench then proceed onto the 8mm bolts. I don't know of a faster way to remove the diffuser than with the flexible extension for the 8mm heads. Here's the link. Kobalt Flexible Extender

Warning to all who purchase this extension, a year ago my first one got wrapped around my hand and I am lucky to not have been injured. The first unit wrapped around and ripped apart across my hand. Luckily there were no scars, and it was only a surprising hard pinch. SO, MAKE SURE YOU SET YOUR DRILL'S CLUTCH PROPERLY! On my particular Rigid Drill, it is only at 6 of 22. Very light setting is needed or the cable will flex and then start to coil.... around your fingers.

I jacked the car up and put two jack stands under the rear rail after diffuser removal.

The connector between the ECU and the O2 sensor is near the underside of the washer fluid. I found and looked at this with a little mirror on a extension wand. Attached is a pic so you can see where its located. They are zip tied to the frame. Reach underneath, find the clips and press down on the tab. Then do a weird single handed tab-depression/plug-separation maneuver.

The plug with the large tab is the connector going back to, correct me if I'm wrong, the fuse box then to the ecu. The O2 sensor plug may still be threaded through the zip tie. Just push it back out the zip tie so you can reuse the tie with the new oxygen sensor.

Get under the car, and release the cable from a small frame clip above the sensor. Pull the O2 plug back to the open underside so you can put your 7/8" "oxygen sensor wrench" over it. I tapped the wrench handle with a hammer to loosen and then was able unscrew the unit by hand.

Insert new sensor, tighten by hand, and only use the wrench to tighten. Put the plug's wire up back in the small clip. Return to the top side and try to work some finger magic to get the O2 sensor plug back into the zip tie loop. Then grab the other plug and put them together. Easy way to tell which way they couple, the larger tabs are on opposite sides of each plug. Try to compress them together, cuss and fiddle, try again, only harder, then stretch and take a breath. Seriously, who puts a zip-tie clip in such an awkward position?

Start the car for a bit and see if the OBDII readings on the STFT (short term fuel trim) are back to decent levels again (+-8 when cold)/(CharlieX correct me if I'm wrong). Lower the vehicle back down and reinstall the diffuser if you know everything works fine.

Oh and by the way. Setting my volt meter to Ohm and using aligator clips to the new sensor's 3 and 4 wires, I received a value around 8 to 9 Ohm. The old unit's reading was 2.4 M Ohm. Does the 2.4 M Ohm or any high number represents a grounded short?

[charliex]

Sounds more like it was open, short would be 0ish ohms, depending on your meter type and what method you used to test it.

cold start -8 / +8 is ok, it should settle to -4 / +4 after warming up thats the range i go for, if you've had a sensor that read badly the ecu might take upto 15 minutes to settle.

one thing to note is that if you do both sensors at once, its very easy to swap the pre/post wiring, if you do that it'll idle badly.