02 Pathfinder: oxygen sensor issues, stalling

[rgk]

P0057, P0158. 2002 Pathfinder.

The car had some trouble starting today in the cold, but started. The battery seems weak. The car had not been started in over a week.

I recently replaced the MAF sensor, which took care of the MAF trouble code. The car ran great the couple of times I took it for a test drive. I never performed an ECU reflash or idle relearn, but as the car ran and idled great, there did not seem to be a need.

Today the service engine soon light came on, after about three minutes of driving, with no symptoms. I checked them and received the codes above: P0057, P0158, as well as a proprietary Nissan code. The two codes were bank 2 O2 sensor voltage high and bank 2 heater control circuit low. I erased the codes, so I can't tell you which Nissan code it threw, but I assume it was an O2 sensor code.

I started the car again this evening, and took it for another drive. This time the light came on after about a minute of driving, and stalled. The first stall occurred as I was pulling out onto the road, and the second came a few seconds later on the road.

I drove the car to a gas station. The car would not go above 2500 RPM, but it wasn't the same fail-safe rev-limiting jerky feeling as had occurred with a bad MAF. It was more subtle.

I pulled into the gas station and read the same codes. Then the car wouldn't start and I had to get a jump.

I got a jump and the car started without a problem. I drove it home - still it wouldn't rev above 2500.

I took the battery to the auto parts store to get it tested, but without a CCA rating on the battery, they can't tell me whether the CCAs are good (I assume they are not). They said the battery is at the last quarter of its life. I checked it while the car was off, and it showed about 11.75 volts.

Any ideas? Perhaps cold weather causing shrinkage and a poor connection at one of the O2 sensor connectors? If so, would this cause stalling and poor performance? I assume it wouldn't, but might a poor connection cause high voltage at the O2 sensor? Could a weak battery be the cause of any of this?

Thanks as always.

[rgk]

Update: got the battery charged, it started the car fine.

Checked the oil cap and noticed yellow sludge. Drained the oil to check for coolant, found none. No apparent coolant loss from the reservoir. I'm thinking this is sludge from the car sitting a while and having multiple cold starts/short drives?

Checked the oxygen sensor connection. Cleaned it out with terminal cleaner, then tried to put it back together but it wouldn't snap. Turns out the rubber gasket inside the harness terminal was preventing it from snapping. I removed it and it snapped together. I thought I had found the problem.

Drove the car about ten miles. It didn't stall, but is exhibiting loss of power above about 2-3k rpm. I tested in 'auto' and '2wd' mode, and it seems that the car has some difficulty downshifting. When I press the throttle all the way to the floor, something clunks from the rear and the car slams into gear. In auto, the front tires seem to be making up for this power loss, but once in a while I hear a noise coming from the front driver's side drivetrain after downshifting.

No check engine light, but pending codes P0455, P0158, and P0057.

At warm idle, the bank 2 downstream (#2) sensor shows a constant 1.25 volts. Under load this drops under 1 v and moves around. But at idle it just sits at 1.25.

The car was NOT doing any of this just last week, when it was 10-20 degrees warmer. Might this be a fluid issue?

Thanks.

[atraudes]

In regards to your oil cap, no worries, you're not making hot dogs in there.

[rgk]

Bwahahahahaha!!

[rgk]

In other news, when I disconnect the bank 2 downstream sensor, the voltage reading on my code reader says it drops from 1.275 volts to about .6. What gives? Shouldn't it say 0?

[rgk]

I unplugged many connections and sensors in an attempt to clean them. I also disconnected the two vacuum solenoids and the plastic vacuum routing box which they are connected to. In doing so, I broke one of the plastic connectors off the passenger side egr vacuum solenoid that allows a vacuum hose to attach to it. I tried supergluing it back on, but it won't stick. I'm on my third attempt.

Now I can't get the car to idle. It starts, runs for a few seconds, then dies.

The worst part is that I can't tell whether this broken vacuum piece is the culprit, whether one of the sensors which I disconnected is loose, or whether I have a broken vacuum line somewhere.

I already found one that was split behind the plastic vacuum distribution housing. I cut off the end, but the rest of it goes down to the center of the block and is unreachable. Now I'm wondering how many more I destroyed, as many of them were brittle. I already replaced three of them.

Will the car run if one of the vacuum hoses is removed?

[atraudes]

The adventure continues, huh?

For P0158 and P0057, I'd say get a new sensor. I've heard a couple stories where the sensor was bad and the ECU never properly detected it. They're not ridiculously expensive and fairly easy to install. P0455 just means you'll have to run through a few troubleshooting steps with your EVAP system.

Before either of those, though, I'd focus on that shifting/rev issue. Since you say it sounds like the front wheels are doing something differently than the rear ones, you could check the fluid level and quality in the transfer case, differentials, and transmission. This could all be due to a vacuum issue, though.

For the vacuum issues: jump on eBay and get a replacement for that vacuum part. You might be able to buy a threaded nipple from a parts store or hardware store to screw in in the meantime. Buy 10 or so feet of vacuum hose and replace all of the vacuum lines. The vacuum hose should only be a dollar a foot or so.

[fleurys]

The symptoms about hard shifting and idle difficulties all point to your maf (again)... I know you changed it, but if I were you, I would simply disconnect it just to see if the problem get worse or better. If the problem does not change with the maf disconnected, then you know your maf is bad... Try that and let us know the results..

[rgk]

Fleurys, I thought about this. The car was already not idling when I tried disconnecting the MAF. It did not idle after disconnecting it, so I assume the MAF is good. Reading the voltage of the MAF while idling and driving (when the car idled fine and drove OK), I saw that the voltage readings checked out OK.

Atraudes, thanks. I'll replace the hoses and check the fluids. I'm letting the super glue cure and will try hooking up the vacuum hose to the solenoid one more time in a day or two. I see here that EGR vacuum hoses can actually become clogged: dreaded-p1130-code-t318804.html

More news: You know how there are two solenoids attached to the vacuum tank? And how I broke the plastic nipple on one of them? Well, the other EGR valve solenoid is bad It's stuck closed and power to the solenoid does not activate it.

This is the part I need: http://www.courtesyparts.com/valve-assy-p-256567.html

Is it possible that this might be causing my hesitation?

Also, it seems like more than a coincidence that the downstream oxygen sensor is showing a high voltage and the O2 heater is not working... simultaneously. It suggests that the wiring might be bad. I'll have to check the resistance between the sensor wiring harness and the ECU. Additionally, from what I understand, the downstream sensor does not affect engine performance, so it's also strange that I began receiving this code right around the time that these hesitation issues began.

[fleurys]

Is there a way you can check the maf voltage now ? (since it is now not idling properly)... You should still get good readings.... this is just to rule out your maf as it is related to your issue.

[rgk]

While replacing the vacuum hoses the plastic piece at the VIAS control valve broke again. I'm over trying to glue it together. Crank, no fire.

However, this did allow me to try an experiment: I covered the little hole created by the break with some duct tape, and each time I cranked it, the car tried to start. I then removed the tape, and cranked again. It tried starting the very first time, but all subsequent cranks resulted in nothing.

So I'm thinking that I have to replace the VIAS. Additionally, the swirl control solenoid is dead.

[rgk]

After replacing the VIAS and swirl solenoids, vacuum hoses, EGR hoses, double/triple checking all intake parts, camshaft sensor resistance and continuity with ECU, and checking for spark, I believe I may have found the problem.

The reading for the bank 2, downstream o2 sensor was bothering me. Why in the world would it show 1.275 volts, when the ordinary reading is 0-1 volts? More puzzling was why the voltage did not drop to zero when unplugging the sensor harness, instead dropping to somewhere between 0.3 and 0.5. The bank 1 downstream sensor dropped to zero when unplugged, but stayed at around .3 to .5 when plugged in, and that's with the vehicle not running.

I decided to investigate the resistances between the two downstream sensors, and here is what I found:

bank 1 power and bank 2 power - 12k ohms
bank 1 power and bank 2 ground - 40.6 ohms
bank 1 power and bank 2 sensor ecu - 12k ohms
bank 1 power and bank 2 heater ecu - 12k ohms

bank 1 ground and bank 2 power - 0 ohms
bank 1 ground and bank 2 ground - 0 ohms
bank 1 ground and bank 2 sensor ecu - 12k ohms
bank 1 ground and bank 2 heater ecu - open

bank 1 sensor ecu and bank 2 power - 9k ohms
bank 1 sensor ecu and bank 2 ground - 9k ohms
bank 1 sensor ecu and bank 2 sensor ecu - 1k ohms
bank 1 sensor ecu and bank 2 heater ecu - open

bank 1 heater ecu and bank 2 power - 1393 ohms
bank 1 heater ecu and bank 2 ground - 1336 ohms
bank 1 heater ecu and bank 2 sensor ecu - 192k ohms
bank 1 heater ecu and bank 2 heater ecu - open

We can reasonably ignore the power and ground resistances, as well as ECU connections that are open. This leaves two connections:

bank 1 sensor ecu and bank 2 sensor ecu - 1k ohms
bank 1 heater ecu and bank 2 sensor ecu - 192k ohms

The ECU resistances between the two sensors, pins 71 and 72, are very low! Shouldn't they be open? I shuddered at the thought of the problem residing in the harness, and decided to check the resistances after unplugging the ECU. They were open (resistance of 1).

Should I assume the ECU is fried? And can I reasonably assume that this is the cause of my condition, which quickly deteriorated from intermittent stalling and lack of power at high speeds, to stalling after ten seconds of operation, to stalling after one second, to hardly a burp, to no start?

If so, how can I try to determine the cause? I would hate to replace it and fry another one. I know after reading several posts here that the IACV may be the culprit, but my idle was never a problem before this happened. Is there any way of testing it? What else may be the cause?

Edit: I did disconnect the harness to the ECU without first disconnecting the battery and read that you can fry it this way.

One final note: after cranking several times, the battery ran low and refused to turn the starter. I then checked the MIL and retrieved a pending P1136 code, intake valve timing control solenoid valve. I have never received this code before. In fact, the entire time the car would not start, it did not throw any code(s).

Edit: According to ECU doctors, when the ECU is fried the following should be checked:

Ignition coils or ignition module
DME Relay or the Main Relay
Faulty spark plugs
Fuel injectors
Idle control valves
TDC and RPM reference sensors
Air flow or mass flow meter
Throttle position sensor
Power supply
Grounds

[rgk]

I notice the FSM has you unplug the ECM harness before troubleshooting the o2 sensor, so now I don't know what to think.

I guess I'll pursue that valve timing solenoid... But I dunno, that just operates oil flow to the camshaft.

The battery is a bit weak, but I am getting 11.9 volts to the ECU.

[Buzzman]

Edit: I did disconnect the harness to the ECU without first disconnecting the battery and read that you can fry it this way.

Doing that is never a good thing.
Unplugging and/or plugging in a circuit board while there is still power to it will most certainly be cause for failure.
That's true of not just your ECM, but pretty much any PCB, from say a computer, or any other electronic device.
I was a tech for 30 years on high tech equipment, and we never had power going to a connector when we pulled or plugged it in.
You may be looking for another ECM. Try e-bay, or a junk yard, etc. A new one is around $1200 dealer price.

[rgk]

Thanks, Buzz. A lesson learned the hard way.

If it did fail, is it typical for it to give out some time later after frying it?

Are there any other tests I can run to confirm this?

[rgk]

Problem solved!!!

Either I am the biggest narrow-sighted buffoon in the history of home car maintenance, or someone drained my gas tank.

The oxygen sensor still shows 1.275 volts, but driving is back to normal. Full power and no shifting issues.

[atraudes]

All that cause the tank was empty? Any more codes being thrown?

[rgk]

Yes. I found out only after hooking up a fuel pressure gauge and opening up the gas tank.

It still sputtered a bit after putting in just two gallons, but half a tank cured it.

A five mile or so drive showed no code, no issues. Just the pending o2 sensor code. Still not sure what is causing the high voltage with the sensor unplugged.