1997 Q45 P0136

Post by **fontana dan** » Wed Dec 14, 2022 7:17 pm

This code has set twice now. "Bank 1 downstream o2 circuit". Looked at live data and seen something suspect. It will go in and out of open loop while idling. Got under the car, downstream o2s and connectors look original, connector has power on pin 4. any advice for testing the signal portion of this circuit?
Engine operating temp, idling
Coolant temp: 155F
fuel trim 20% both bank 1&2.
bank 1&2 upstream o2: 1-9v switching in closed loop.
During function test
bank 1 downstream unresponsive at .2v during test.
bank 2 downstream switches slowly .2-.7v.

Previous thread I made about P0171 on same car. After a lot of miles that code is no longer set in pcm.
1997-infiniti-q45-p0171-t631207.html

Post by **VStar650CL** » Wed Dec 14, 2022 7:46 pm

Flatline at 0.2V with the cats lit is definitely unhealthy. The +20% alpha isn't real healthy either, but it isn't causing your immediate issue. HO2S's usually won't read anything if they're open circuit, but that depends a bit on how they're biased. You can eliminate a wiring issue by yanking the connector and see if the reading goes to one of the rails. If not then you might have a wiring issue, otherwise I'd say it sounds like a dead sensor.

Post by **fontana dan** » Wed Dec 14, 2022 8:52 pm

The downstream sensors read .000v with the key on engine off regardless if they are plugged in or not.
I think I will plan on replacing the sensor.

Post by **fontana dan** » Sun Jan 22, 2023 12:33 pm

Replaced bank 1 downstream o2 sensor and it seems like all the o2s are functioning now. Will report back after the car runs a drive cycle.
Also getting a P0400 "EGR flow incorrect." Is it possible for EGR to affect the a/f mixture of the engine to cause +20% alpha? I wouldn't think so but I'll have to investigate.
Also replaced thermostat so engine is now running at correct operating temp 170F.

Post by **fontana dan** » Sun Jan 22, 2023 2:38 pm

Post by **3Q Jay** » Sun Jan 22, 2023 3:37 pm

fontana dan wrote: ↑
Sun Jan 22, 2023 12:33 pm
Replaced bank 1 downstream o2 sensor and it seems like all the o2s are functioning now. Will report back after the car runs a drive cycle.
Also getting a P0400 "EGR flow incorrect." Is it possible for EGR to affect the a/f mixture of the engine to cause +20% alpha? I wouldn't think so but I'll have to investigate.
Also replaced thermostat so engine is now running at correct operating temp 170F.

Sounds like some progress.
EGR will definitely affect A/F R when it's cycling, but it shouldn't be cycling at idle.
Could the P0400 be an artifact of a config mismatch while you were doing the work? I guess you'll see if it persists after reset.
Verify your hose connections, including the BPT.
Does the EGR valve pulsate at warm off idle as shown in your FSM excerpt?

Post by **fontana dan** » Mon Jan 23, 2023 8:40 pm

Thanks for the advice Jay.
P0400 code has set a handful of times over the past 1000 miles.
Today I removed EGR valve for inspection, the valve seats smoothly and the diaphragm does not leak vacuum. It is not opening at idle when the engine is cold or hot.
Did clear the tube from BPT to EGR which was plugged with carbon. I do not believe it is related to the idling lean condition. There has to be a vac leak hiding somewhere.

Post by **3Q Jay** » Mon Jan 23, 2023 9:00 pm

longshot....but what happens when you pull the single vac hose to the EGR valve at idle? put a vac gauge on the end of that hose and look for even a small amount that could be pulling open the EGR valve (even a little) at idle.
Also, remind me if you have replaced the soft gasket between the upper and lower plenum? OE Nissan part (#14032-6P010)?
There was a TSB waaaaaay back on the early FGY33's for bad gasket. That could definitely be a source of unmetered air....

Post by **VStar650CL** » Mon Jan 23, 2023 9:01 pm

The three biggest sources of mystery vacuum leaks are the PCV system, fuel pressure regulator (if it's vacuum operated), and the brake booster, in that order. The purge system can do that too, but the ECM will usually catch that because there's a pressure sensor on the evap.

Post by **fontana dan** » Mon Jan 23, 2023 9:47 pm

Last summer I removed upper intake to replace gasket 14032-6P010. Replaced both PCV valves. No change. Did a couple of smoke tests and could not find anything. Afterward kind of forgot about it because there is no drivability complaint.
I will test those sources Vstar mentioned and go over the system again.
@Jay The EGR valve does nothing when vac hose is removed at idle. No vacuum is present.

Post by **3Q Jay** » Tue Jan 24, 2023 5:08 am

good call on the gasket. Did you also completely pull out and clean the EGR "piccolo tube" while the upper intake was off (impossible to do while mounted)?
I was thinking overnight that perhaps a clogged internal tube (they are a b!0tch to clean) could be related to your EGR flow code.

Post by **VStar650CL** » Tue Jan 24, 2023 6:43 am

EGR codes aren't something we deal with much these days, so I looked your P0400 up in Identifix. It's actually a temperature code, the ECM infers whether the EGR is working by the temperature in the system. So you can tell whether the code is electrical or functional by measuring the output from the EGR temp sensor. It should typically read 2.5~3.5V at warm idle (when the EGR isn't operating) and quickly drop to 1V or less when the EGR is activated. That's easiest to test by putting vacuum on the valve while an assistant holds the RPM's up (the engine will want to stumble and stall if the valve is working properly and has flow). If the engine doesn't stumble then either the valve is bad or there's no flow. If it does stumble but the voltage remains above 1V, you probably have a bad temp sensor. The sensor has a very high resistance range, Mohms when cold and 80~700 Kohms in the working range, so it will be pretty insensitive to wiring issues short of a completely open circuit. The vast majority of the confirmed fixes in Identifix were plumbing issues, either the EGR exhaust tubes or the vacuum hoses to the EGR/BPT. Keep in mind that a smoke test won't show up a problem in the EGR actuator or hose, because the smoke won't have a pathway when the solenoid is closed.

Post by **fontana dan** » Tue Jan 24, 2023 8:40 pm

I did not clean the tube between the EGR valve and exhaust manifold. It is another possibility. The engine does not stall when i lift the valve manually but it flowed acetone on the bench...
Thanks for looking it up @VStar. I would try some driver seat diagnosis but I can't see that PID with my scanner. For now I discontinuing the procedure until ECM completes a drive cycle. Thank you for your time.

Post by **VStar650CL** » Tue Jan 24, 2023 8:59 pm

If the engine doesn't stumble but you know the valve is good, that exhaust feeder tube is clogged for sure.

Post by **3Q Jay** » Wed Jan 25, 2023 11:00 am

fontana dan wrote: ↑
Tue Jan 24, 2023 8:40 pm
I did not clean the tube between the EGR valve and exhaust manifold. It is another possibility. The engine does not stall when i lift the valve manually but it flowed acetone on the bench...

Sounds like something to look at. But, for clarity, I was referring to the piccolo tube that is INSIDE the upper plenum, between the EGR valve and the actual intake runners. Unless you have taken that out and cleaned the crap (literally) out of it I can almost guarantee you that it not only looks nasty, but is a plug big time.

Post by **VStar650CL** » Wed Jan 25, 2023 11:04 am

3Q Jay wrote: ↑
Wed Jan 25, 2023 11:00 am
Sounds like something to look at. But, for clarity, I was referring to the piccolo tube that is INSIDE the upper plenum, between the EGR valve and the actual intake runners. Unless you have taken that out and cleaned the crap (literally) out of it I can almost guarantee you that it not only looks nasty, but is a plug big time.

+1. I don't know enough about old Q's to say whether the clog is most likely on the inlet or outlet side of the EGR Valve, but if it doesn't stumble with manual activation, one or the other is definitely clogged.

Post by **fontana dan** » Thu Jan 26, 2023 8:43 pm

Thanks for the tips guys. It would have been different if I knew about this issue when I took the intake apart. The vacuum leak still perplexes me.
This car needs more attention to the suspension and driveline before emissions systems. Rear struts are blown out as well as the diff carrier bushings. Transmission slips.

Post by **3Q Jay** » Fri Jan 27, 2023 8:57 am

It's the old saying....you don't know what you don't know.
Part of the joy of Q ownership (for the curious minded, at least semi-skilled hand) is figuring out the "why" of something that is. Can be rewarding once it's sorted out.
Hang in there.
Just a guess...is the RE4R03A slipping you speak of an overspeed on the 2-3 shift?
Have you dropped the pan (not just drained) and replaced the screen?

Post by **fontana dan** » Sat Jan 28, 2023 12:03 pm

This is an entirely different can of worms however...1st gear is weird especially when the car is cold. 1-2 upshift is rough at WOT. Very delayed engagement from neutral...car will hesitate 15+ seconds after a cold start. 3-4 upshift quality can also be spotty. When shifter is placed in "2" position, car still starts out in 1st gear. Dropped pan and replaced filter, no change.
The performance of the trans is directly related to ambient temp, and presumably trans oil temp...
I want to do a pressure test on the forward clutch circuits. Anyone know offhand the thread pitch of the pressure plugs? RE4R03A
How is the parts market for this transmission?

Post by **fontana dan** » Thu Mar 16, 2023 8:13 pm

Ok I've put about 1k miles on this car since replacing 1 downstream o2 sensor and cleaning the EGR valve. Car is happy, no codes set. All monitors completed on the drive cycle.
I sure love driving an old car with NO warning lights on the dash! I also like that the car never makes stupid dinging or chiming noises.

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