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Discussion Starter #1
Hi,

as stated in the title I have scanned my Jet (2.7) and got P0134 (O2 Bank1 upstream/pre cat no activity detected). However when I chart its signal it oscillates btw lean & rich as it should.
One more thing makes me wonder:
part load long term fuel trim is at 45% for bank1 but only 25% for bank2.

Is my O2 B1/S1 going bad ?

B.t.w.: No CEL (yet), car has 155'km on the clock.

Why did I scan it ?

My wife drove it. Took off, went down a slope and the engine just shut off. Scared her to death since power steering went out etc. ...
She stopped, restarted the engine and all appeared to be fine, drove home with no more incident.
 

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With a no activity code or a slow response code I'd check that the sensor heater circuit is working properly. It won't start switching until it gets hot which can take longer than normal if the heater circuit has a problem. You could take a look at the voltage output from B1S1 & B2S1 from a cold start to see if they both start switching at the same time or if activity from the B1 sensor is delayed while the sensor heats up from the exhaust gasses.


Scottie.
 

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random stall could be unrelated to the O2 sensor issue. My old Saturn had a random stall without trouble code and it turned out to be that the fuel pump was going bad (intermittently failing).
 

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random stall could be unrelated to the O2 sensor issue. My old Saturn had a random stall without trouble code and it turned out to be that the fuel pump was going bad (intermittently failing).
Hello James.

I suppose it's also possible that the OP's O2 sensor issue is a symptom of a fuel pump problem. Low fuel pressure might also explain those high LTFT figures too.

It would seem odd (to me, at least) for a failing fuel pump to cause the engine to stall while going down a slope though. Fuel delivery would be at it's minimum going down a slope (low or no throttle) so you'd think even a failing pump would be able to meet demand in that situation. What was your experience with the Saturn? Was the stalling truly random or did it tend to happen more during high or low throttle settings? I've never come across a failing fuel pump, only pumps that were totally dead, so I'd be interested to hear what happens in a real word situation when the pump is weak/failing.

Scott.
 

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Discussion Starter #5
Thanks guys for your inputs.

I'll try that O2 heater test by charting both upstream O2s in parallel from a cold start.
It may just have been a false alarm. When searching here I found note about a TSB stating need to update ECU soft on 2.5 EF Sonatas when throwing that P0134 code - just because from factory the threshold was set too tight for 'no activity detected'.

We'll see.

Actually I also had the train of thought going that way that the fuel pump fading would cause the higher trim numbers, but it should be affecting both banks in a similar way, no ? Need to see where's the best place to measure fuel pressure.
 

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Hello James.

I suppose it's also possible that the OP's O2 sensor issue is a symptom of a fuel pump problem. Low fuel pressure might also explain those high LTFT figures too.

It would seem odd (to me, at least) for a failing fuel pump to cause the engine to stall while going down a slope though. Fuel delivery would be at it's minimum going down a slope (low or no throttle) so you'd think even a failing pump would be able to meet demand in that situation. What was your experience with the Saturn? Was the stalling truly random or did it tend to happen more during high or low throttle settings? I've never come across a failing fuel pump, only pumps that were totally dead, so I'd be interested to hear what happens in a real word situation when the pump is weak/failing.

Scott.
I was trying to make the point that maybe the car has 2 problems, one problem associated with the O2 sensor and another unrelated problem that caused the stall. I used the example of the fuel pump because that would not be associated with an error code.

Have to respond about my Saturn another day when I have more time.
 

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Discussion Starter #7
Scanned it again yesterday, no errors and L.T. fuel trim numbers at -2% both banks - which is healthy.
I think for now I'll not do anything but scan it every now & then.
 

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Hello James.

What was your experience with the Saturn? Was the stalling truly random or did it tend to happen more during high or low throttle settings? I've never come across a failing fuel pump, only pumps that were totally dead, so I'd be interested to hear what happens in a real word situation when the pump is weak/failing.

Scott.
Long story short about my Saturn:
In January 2015 my Saturn started having an intermittent, random stalling problem. 1999 SW1 (small wagon) 4 cylinder engine, manual transmission, about 198,000 miles on the car. I couldn't fix it and the local independent shop couldn't fix it. I thought the only explanation was that the fuel pump was going bad (everything else had been ruled out). That would have been a pricey repair because you have to drop the gas tank to get to the fuel pump. So I sold the car and bought my Hyundai! Guess I was wrong about the fuel pump, must have been some other problem. Regardless, all's well that ends well, I feel good about the decision to sell the car and I'm really happy with my Elantra GT (no problems at all so far, knock on wood)

more info if anyone is interested:
The car would stall every week or two, it really seemed to be random. The engine would hesitate and sputter, the fuel gauge read empty (even though there was plenty of gas in the tank) and the tachometer read 0 (even when the car was moving). The car stalled a) while idling several times b) one time in stop and go traffic c) once at about 35 mph and d) twice at about 55 mph. At first I thought it was bad gas (water in the gas tank). I took the car to the local shop and they cleaned the throttle body, that didn't fix it. I was usually able to get the car restarted. It seemed to help if I turn the ignition key to the ON position for a few seconds before trying to start it. It also seemed to help if I got out of the car and shook the car (to swish the gas around in the tank). One day the car stalled when I was at a shopping center, I was able to restart the car numerous times but it always stalled again. I drove around the parking lot to test it, but it kept stalling. So I had to get towed to the local shop. This time they replaced the Crankshaft Position Sensor and the fuel filter. Car drove fine for a few days, but then stalled again. I took it back, the head mechanic asked me to leave it for several days so he could test drive and perform diagnostics. He couldn't find anything wrong with the car, but he replaced the Crankshaft Position Sensor again (no charge) in case the previous one had been bad. Wouldn't you know a few days later the car stalled again. My brother had a theory that it was the fuel pump failing. My brother can fix anything: TVs, microwave oven, computers, vacuum cleaners, chainsaws, telescopes, cellos, Subarus, etc., and he knows a lot about electric motors. His theory was that the electric motor in the fuel pump was in the final stages of its life cycle and was acting erratically. That made sense to me. But I guess that is good in theory and not the way that fuel pumps actually behave in practice.
 

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Discussion Starter #9
Gotta revive this one.


Went off again yesterday (wife again ...), luckily in our driveway ... restart, everything fine again.
No clue what that is. Fuel pump relay maybe ?

car has now 181' km, i.e. 26' km more than when I first posted about this 3y ago.



In the meantime it has gotten a new crank sensor and a new fuel pressure regulator (both OE/Mobis, not aftermarket). I account initial fuel trim issues to the regulator dribbling fuel into intake #6 ... . This case was deemed closed from that end. L.T.Trim numbers were very close for B1&2 with new regulator installed.


Still it has P0134 showing up occasionally. Haven't replaced related O2S yet since when charting voltage in the past it just took some more time to start oscillating compared to the other bank.
Looking at charts today it appears it must be replaced now.


What confuses me is that when I chart B1 and B2 sensor, I see bad behavior on B2 but the DTC says B1 bad.
So which one to replace ? Both ?
 

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Discussion Starter #10
Now also throwing P0154, 1166 and 1167. Running rough, stinks & smokes from the tailpipe, dies in idle, not going to closed loop.


I'll order two O2S fit and see ...
 

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Discussion Starter #11
solution

To summarize: fitted new MAF sensor (Pierburg 7.07759.10.0) and all is fine.


Now have 2 new HO2S (universal type, Bosch) to put on the shelf.


Experience says:

Parts you have on stock don't break in the car. Like it doesn't rain if you carry an umbrella.


Details (for the technically interested):
When it ran badly, I noticed that air flow numbers were off (70kg/h at idle, normal is ~20). Unplug MAF and it immediately ran way better. Plug it back, still ran ok but now air flow was reading low (12kg/h). Noticed greasy stuff in connector (PO probably sprayed it in), cleaned it out with brake cleaner spray.
Decided to add a MAF sensor to the parts order ...


Nasty side story: When using dedicated Hyundai software on my Autoboss V30 diag tool the O2S readings were strange (as posted above) even with the new MAF.
When using the generic OBD2 program on the same device all was fine, both banks nicely oscillating btw 0.1 and 0.95V with correct frequency. Also my little Launch Creader5 (clone) showed it like that. So my conclusion is: there is a bug in the Hyundai Diag software (v3.6) that was fooling me for long time.


Fuel trim issue initially reported was just due to leaking pressure regulator - and long gone.


Next things to do: timing belt is due (only 36'km run but 6 years are over), serpentine belt tensioner is worn and needs replacement and the left front strut mount is shot (again) ...
Front brakes need new pads & rotors, too.
 

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Glad you finally got to the bottom of this problem. And thanks for taking the time to post the detailed update too, much appreciated.

Bugs in the diag tool software can have you chasing you tail...LOL. Funnily enough I was called out to a garage just last week to help them diagnose a problem with an exhaust gas temperature sensor. The sensor output on the scan tool data list was stuck at 0°C so they replaced the £110 sensor, but it was still the same. They asked me to check the wiring and I couldn't find any fault. I connected my scan tool and rechecked the sensor output and it was correct. Turns out it was just a glitch in the software of their fancy Snap~On scan tool. £110 for a sensor + my labour charge all for nothing.

I think all garages should buy Snap~On scan tools. I'd make a fortune :laugh:
 

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Maybe the heater inside the O2 sensor is open. The sensor has 4 wires, 2 for sensing and 2 for the heater, I don't recall the colors nor the heating element resistance, but has to be around 10 Ohms.
 

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Discussion Starter #14

Thanks for your reply but you may have missed the point that the problem is long solved and was entirely caused by bad MAF sensor and leaking gas pressure regulator. Bad heater of O2S has its own code (like P1116), btw. and that never showed up on the way ...


O2S is the most replaced part for no reason - even / especially in professional shops of certain kind. You can make good profit and you can easily argue with customer:

'look, here's an O2S related code, so we must replace all 4-8 sensors in your ride before we can properly diagnose the actual issue, sorry for the 1200-2000$ bill ...'


In most cases O2S just shows that something is fishy upstream.
 
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