I don't see how you could reverse them....

But if you did, you wouldn't get down stream codes. All down stream codes depend on working upstream cats, as they are thrown based on incorrect differentials from the upstream.

 

Thanks for all the input and suggestions.

I DID use a multi-meter and check both front o2 connectors for power and each wire between the connector and ECM for continuity before we put in the 3rd set of sensors. The electrical diagram definitely helped me there, and another person for help was necessary too! I doubt anything has changed since then. I really thought getting in the proper sensors would do the trick.

Next step: I will check the connectors for power again as well as each of the other 3 wires in each connector and the ECM...love me some pinouts.

If the connectors prove to be functioning properly, what is my next step? Do I then check the wires and connection between the ECM and ECU? Or assume the ECM or ECU are malfunctioning?

Thanks again, DIIB.

 

I think you're right and you have bad ECU that's ignoring the input from the O2. You can verify this by probing the connector with everything connected up. If the O2 is working right (since yours are new, they should be) it'll still send the signal to the ECU regardless of if it's doing anything with it.

Pins 1 & 2 on the sensor carry the signal. It should be between 0.1 and 1 volt dc. 0.45 ish if everything is working fine, on the high side if it's rich like you are or on the low side if it's lean. If everythings normal it bounce back and forth a little as the ECU balances it all out.

Pin 3 & ground should be constant 12vdc from the fuse box. Pin 4 & ground should read 12 VDC or 0vdc as the ECU cycles the heater on and off.

I'm not 100% positive, I'm in the office avoiding work right now, I'll crawl under my truck when I get home and check it out. Mine's an '03 but the O2 system should be the same.

 

I couldn't figure out a way to check the O2 sensor connector without burning myself on the cat. Also I'm not sure how you could hook these guys up backwards, the way it's laid out under there, you would have to put in some effort to screw it up. And burn yourself in the process. I ended up back probing the connector on the ECU, which was equally frustrating, just not as hot.

Pins 1 & 2 did yield what I expected: a fluctuating voltage hovering around the 0.45V mark. As I don't have an O2 problem, that makes sense. Occasionally it would spike to the extremes at either end, about 0.2V to 0.8V. I had to set my meter on manual. The voltage bounced around to much for the autorange on it keep up. It's around 17 yrs old, so it may be just my meter.

I got a constant 0vdc on pin 4, not sure if I was doing right or if the ecu was keeping the heater off, I had just finished driving it home from work after all.

I didn't test pin 3, it's not present on the ecu and the cat was just to damn hot for me reach my arm up there to test it on the sensor.

Hope that helps!

 

That really sounds like an ECU issue. It seems you've ruled out everything other than the physical connector on the ECU.

Have you tried opening it up to see if you have any gunk growing in there (maybe it got wet) or tin whiskers causing problems?

 

did someone pinch the harness under the intake or the heads?

 

No. He probed at the ECU, well past that point in the harness, and found proper readings.

 

Well, hopefully in the next day or so I will get around to testing the fronts (again) for power and continuity on all 3 wires in both connectors AS WELL AS the rear o2 sensors circuits too, just to rule those out as possibly causing problems.

I have NOT opened up the ECU and checked it out yet, but that should definitely be done and will be fun for me to see.

I will keep this updated, wish me luck.
Thanks, DIIB

 

Ok, getting closer. Deep breath.

Swapped out all 4 o2 sensors with known working sensors and no change in readings (rears worked and no activity on both fronts, sat at .45). So, that should cancel out the rear sensors being a problem or that my 4th set of new front's are also defective.

I went of out town and left it with my mechanic and he said that the ECM should be grounding or sending a ground signal...well it supposedly wasn't, and so he stripped back the cover around the wires close to the o2 connector and grounded the wire himself and the readings instantly changed and started to adjust. I'm fairly positive that is my understanding of what he did, but i'm still learning all this electrical crap and am now printing off the entire Electrical Troubleshooting Manual at kinko's!

So, where does that leave me? Does that confirm that my ECM is bad? Or is there just a problem with the wire going from the ECM that should ground?

I've talked with Paul in Orlando and he's got an extra known-working ECM that he keeps in his shop for this purpose that he can hook up and re-flash to confirm it is the problem...but I don't want drive to Orlando and back getting 10mpg's or less just to confirm the problem, then have to make the trip again after getting a new ECM and installing and reflashing.

I've got a multi-meter and am willing to learn, but I need idiot-instructions.

Thanks as always, DIIB.

 

Saw this once. Check the ecu grounds. If ok, ground the O2's to the block somewhere, it will save you from buying a new ECU.