Doppelgänger

iTrader: (12)

So a little background here. I sold the '02 back in April and acquired the MSM from Jenn. On a few random occasions the car would stumble and the CEL would flash, car ran like crap, clear up and the CEL would then then go steady. Diagnosed it as a bad coil pack. Replaced coil pack. Not long after CEL would kinda come and go randomly....then stayed on. Scanned it and got P0421 catalyst too low. My intuition tells me the bad coil pack caused raw fuel to the exhaust can fucked over the converter. Joy.

Cleared the code and I've now been getting P0037 since.

So given the situation of moving back to the other side of the country, and needing to get the car to pass emissions, I'm trying to fix this....albeit a bit unconventionally. Don't want to spend the $$$ and time to swap the PITA downpipe/cat.....I bought a O2 sim and one of those spacers with a small cat core in it to try.....as it is a lot less effort.

What I've done:

-Crawled under car, removed sensor, turned key to "on" and put my hand on sensor.....stays cold.
-Put a meter on the heater circuit wires and got 12.3v
-Replaced OE sensor with Bosch 15740 universal 4-wire post-cat sensor.....before putting it into the exhaust, let it hang and turned the key to "on" and verified the sensor started warming up...and had 12.3v
-Connected a scan gauge to the OBD port and fired up the car and cleared the DTC.
-With scan gauge still connected, viewed live data and it showed the front O2 sensor voltage moving within the correct range, but the downstream sensor was showing 0.00v still.....even though the sensor is clearly getting heater power.

W T F

I was hoping to verify the downstream sensor to be working, then install the simulator figuring the converter is failing and it would prevent the CEL/DTC from coming back....since the goal is to eliminate the P0421 from coming back.

What might cause the data to show 0v on the circuit when I have physically verified the sensor is getting voltage/warming up? A bad heater circuit in the ECU??

Also, AFAIK the two black wires for the heater circuit have no right/wrong way to be wired up... I.E. there is no +/- to worry about....as long as they're hooked up. The blue is signal and the white is ground....all connected correctly to the universal sensor I installed. I've verified 239 times that all the wires colors are correct.

W T F

Helps?

SpartanSV

Sounds like signal isn't getting from the sensor to the ecu or the sensor isn't actually getting ground.

Use a DMM to measure voltage on the signal wire at the sensor. If you're seeing voltage fluctuating like it should then do the same at the ecu. Also measure continuity to ground from the sensor ground wire if you aren't seeing voltage on the signal wire at the sensor.

Why would you suspect a bad heater circuit when you said you verified it was warming up?

curly

iTrader: (25)

The heater circuit has nothing to do with the sensor, it just heats it up. You probably have a bad secondary o2 sensor.

Doppelgänger

iTrader: (12)

It's brand new :(


Spartan- I did use a DMM on the 2 heater wires to confirm 12v (along with physically feeling the sensor warm up as previously stated). As for the other 2 wires, signal and ground....will try shortly and report back.

What stumps me is that I understand is that the heater circuit and the signal are 2 different things the ECU monitors, but please correct me if I am wrong. Basically, my mentality is that if I were to have a perfectly functional rear O2 sensor, and cut the blue/signal wire, I'd get a code for no input, and not get a code for heater circuit.

curly

iTrader: (25)

Oh I thought you said you replaced your primary. Makes more sense now.

Id put your multi meter on the signal wire, see what it's saying, maybe check continuity to the ecu. I've seen secondary o2 sensor errors after seat installs and ****.

Doppelgänger

iTrader: (12)

Yeah, I've read a thread or two. I did check things back there and all was well.

Ok, performed more probing.....hehehe....probing.

At the connectors under the car where I spliced the new sensor in:
Black/heater: 14.2-14.3v
Black/heater: 0.03v
Blue/signal: 0.75-0.79v (dithering up and down 0.05v and the average range was increasing overall... 5min later it was 0.79-0.84v)
White/ground: -0.03 solid


Checked the 3P (heater?) pin at the ECU and got 0.26-0.31v....dithering. Maybe I didn't have the probe pressed into the pin hard enough.
Pin 4AA (signal) was 0.78v....dithering (didn't feel too comfortable jamming the DMM problem too hard into the connector)

Are these the values I should be seeing?

Doppelgänger

iTrader: (12)

Update-

Seems maybe some probing is what she wanted. After putting everything back together and clearing the pending P0421, went for a bit of a drive in an attempt to get through some of the drive cycles.....so starting, stopping, turning the car off and on, cruising at different speeds. After 140 miles, I plugged the scanner back in and was greeted with no pending codes......and was showing voltage on sensor 2. So it looks like all might be well. Maybe something was not quite tight and checking over it one last time corrected it. If anything, maybe some of the info I posted here will be useful for someone else later.

SpartanSV

I believe on a narrow band sensor 0-1 volts is what it should be bouncing between. The measurements you got were what I would expect to see with everything functioning. Seems there was a connection issue somewhere.