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Allante 1989 export running on LPG
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Discussion Starter #1
This has been going on for a while.
I get the check engine light
Code P0152 02 Sensor Circuit Low Voltage Bank 2 Sensor 1
Sometimes also
code P0174 Cadillac - Fuel Trim System Lean Bank 2
And sometimes
P1599 Cadillac - Engine Stall Or Near Stall Detected
I presume the second 2 are related to the first one.
I have a service manual.
I have changed the oxygen sensor but the problem came back, It was a non brand sensor could this be the problem.
I have checked for vacuum leaks but cant find any.
I have checked the intake from the air filter, no issues.
I have changed the following
wires
coil pack
idle control
MAF sensor
MAP sensor
EGR
PCV
cleaned the spark plugs
Air filter
Some of those parts were used from a parts car.
I can eliminate the injectors and fuel pressure issues as this car runs on petrol and LPG and the problem is on both.
The car sometimes stalls. normally when it's going from closed loop to open loop, then it's fine.
Slight misfire at idle.
Any help appreciated.
 

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2010 DTS
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I presume the second 2 are related to the first one.
No, an O2 sensor should not cause a stall.

I have changed the oxygen sensor but the problem came back, It was a non brand sensor could this be the problem.
Possibly

A lean fuel trim on bank 2 means a vacuum leak on that bank. Check the PCV clean air line on the bank 2 cam cover.
Also check the manifold over pressurization relief valve in the tunnel behind the P/S pump to be sure it is seated properly.



 

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2002 Eldorado Biarritz
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451 Posts
Three things immediately come to mind.

1. Where was the O2 sensor physically located on the car that you replaced. Bank 2 is the bank closest to the radiator on FWD Northstars

2. How thoroughly have you checked the O2 wiring and connector? In some locales the connector for the O2 has been known to suffer from water intrusion and corrode. The wiring also has several places that it might rub and short out on the engine or transmission.

3. Off brand O2's are questionable at best.

One last thing. O2s can and do cause stalls just several months ago I helped another repair shop diagnose an issue very similar to yours. In that case it was corrosion on the connector.

"The car sometimes stalls. normally when it's going from closed loop to open loop, then it's fine."

When you said this did you mean going from open to closed? Normally a car starts in open and goes to closed. Of course in your situation the fault codes are probably setting and forcing it back into open loop and maybe that is what you are seeing.
 

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2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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Never seen an '02 sensor cause a stall. They're only effecting fuel trim, they have no effect on ignition and cannot make drastic instant cuts to fuel delivery.

Random stalls without codes, it's much more likely a CKP issue. IIRC the stalking when going to closed loop sometimes occurs with faulty CKPs as well.
 

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2002 Eldorado Biarritz
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Never seen an '02 sensor cause a stall.
You just haven't diagnosed enough stalls. Do it long enough and you'll see it all. But, I certainly wouldn't call it common.

They're only effecting fuel trim, they have no effect on ignition and cannot make drastic instant cuts to fuel delivery.
Fuel trim is extremely important. In fact it is my single favorite PID for driveability diagnostics. It doesn't need to be instant or drastic. The fuel trim system is the check and the balance. Nothing overrides it unless a fault is detected by the PCM. Once it shows a low voltage it will add fuel. If it is a circuit or sensor issue it will continue to read low and the PCM will continue to increase injector duty cycle. This continues until the vehicle either faults out of closed loop and resumes open loop operation and then runs correctly based on MAF, MAP, ECT, IAT, etc. Or it continues until the mixture is too rich to support combustion. Then you get misfires and potential for stalling. I believe this to be basically what the OP is describing and have seen it before.

Random stalls without codes, it's much more likely a CKP issue. IIRC the stalking when going to closed loop sometimes occurs with faulty CKPs as well.
He has codes, three of them. Stalling when transitioning to closed loop due to a defective CKP doesn't make any sense. If someone observed this it was likely due to coincidence and not cause and effect.

The fact that the car can alternately run on gas and LPG complicates things as long term fuel trim values will differ between systems and if they share the PCM fuel management system is some way the PCM would need to relearn long term trims every time the fuel is switched. I am curious as to how the LPG system manages fuel trim.
 

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Allante 1989 export running on LPG
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Discussion Starter #6
Thank you
Yes with the stall I meant from open loop to closed loop. when its heating up in the morning, this only happens occasionally.
I did check the over pressure relief valve as best as I can see, I also sprayed it when I was looking for a vacuum leak.
I did check the sensor wiring and connector, If there was a loose connection I think the code would be a different one.
The LPG takes the signal from the injector wires to control the lpg system. I have run it on just petrol and the problems are still there.
 

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2002 Eldorado Biarritz
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Thank you
Yes with the stall I meant from open loop to closed loop. when its heating up in the morning, this only happens occasionally.
I did check the over pressure relief valve as best as I can see, I also sprayed it when I was looking for a vacuum leak.
I did check the sensor wiring and connector, If there was a loose connection I think the code would be a different one.
The LPG takes the signal from the injector wires to control the lpg system. I have run it on just petrol and the problems are still there.
P0152 indicates that the signal voltage is hanging low and not responding to fuel enrichment. Four possibilities exist.

1. Faulty Sensor (Possible given you used an off-brand sensor, but I believe you said the problem was present before the sensor replacement)

2. Faulty Sensor Heater, O2s need to be at a certain temp to operated correctly usually about 600 deg F. That is why cars start in open loop until the sensor can heat up. But, heater circuits are monitored and usually set codes when they have issues.

3. Circuit fault. This encompasses the wiring and the circuitry inside the PCM. These signal circuits are very low power. Very low available current. Even small amounts of resistance can drop signal voltage low or bias the voltage low. Also, if the signal wire rubs through it will ground out and not burn up the wire and not blow any fuses. It will simply pull the signal voltage down to zero.

4. Faulty PCM. The PCM is receiving the correct data but interprets it incorrectly.

In my shop I'd first monitor B2S1 voltage during warm up. I'd want to know where is the voltage when the system transitions to closed loop. If it stays low I'd want to wait and see if it ever begins to cycle or does the vehicle fault out into open loop fault (OL Fault) and only continue to run in that fault mode. If the voltage begins to cycle. I'd suspect a lazy sensor or a weak heater. I'd probably then check pin tension and corrosion at the connector and if no issues were found replace the sensor with OE and retest.

If the sensor never began to cycle I would manually add propane enrichment with a torch set through a vacuum line and see if the sensor ever responded to enrichment. If it did not respond I would back probe the sensor signal wires on the back side of the PCM connector with my oscilloscope and see if what the scope saw at the sensor agreed with the PCM data stream.If they did not agree as in I saw something other than low voltage I would now know that the PCM has an internal issue. If what I saw was consistent with the PCM data stream, I'd move to the O2 sensor connector checking first the PCM side and then the O2 side. If the voltage was still stuck low on the PCM side of the connector I'd move on to the other side. If the voltage was different from the data stream at that point I would know that the problem lies in the wiring between the sensor connector and PCM. If the voltage is still low on the pcm side of the O2 connection but is different on the O2 side the problem is in the connector. If the voltage stays low everywhere leave your leads attached to the O2 side of the connector and disconnect the sensor from the wiring harness. if the voltage stays low suspect a dead sensor. If the voltage changes suspect a short to ground in the engine harness and test accordingly. I tried to cover all the bases. I suppose this testing could also be done with a quality multimeter (preferably one with a bar graph as well to report rapid changes). But my preference is scope or graphing multimeter.
 

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Allante 1989 export running on LPG
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Discussion Starter #8
The fact that the car can alternately run on gas and LPG complicates things as long term fuel trim values will differ between systems and if they share the PCM fuel management system is some way the PCM would need to relearn long term trims every time the fuel is switched. I am curious as to how the LPG system manages fuel trim.
The lpg system has a separate management system and takes the signal from the injectors which are spliced into the injection wires, and then when it changes to LPG the petrol injectors are switched off and the lpg solenoids fire. The car still thinks it's on petrol, the length of time the lpg injector is open for is not the same as the petrol times and is set up when the system is fitted and will adjust as the petrol times change. It's a good system and you save around 50% on fuel costs.

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Today I got another code P0155 Cadillac - HO2S Heater Performance Bank 2 Sensor 1
I am now thinking it is the sensor.
I had a good look at the wiring to the sensor today, I used the plug from an old front and rear sensor (The rear are the other way around) and tested the wiring with a multimeter and as far as I could test that seemed ok. My time was limited.
I'm really thinking that i should get the correct AC Delco sensor and see if that fixes it.
 

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2002 Eldorado Biarritz
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The lpg system has a separate management system and takes the signal from the injectors which are spliced into the injection wires, and then when it changes to LPG the petrol injectors are switched off and the lpg solenoids fire. The car still thinks it's on petrol, the length of time the lpg injector is open for is not the same as the petrol times and is set up when the system is fitted and will adjust as the petrol times change. It's a good system and you save around 50% on fuel costs.

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Today I got another code P0155 Cadillac - HO2S Heater Performance Bank 2 Sensor 1
I am now thinking it is the sensor.
I had a good look at the wiring to the sensor today, I used the plug from an old front and rear sensor (The rear are the other way around) and tested the wiring with a multimeter and as far as I could test that seemed ok. My time was limited.
I'm really thinking that i should get the correct AC Delco sensor and see if that fixes it.
With the heater code now set. I would strongly agree. In order to save time when I have a heater circuit code for a single sensor I usually start by replacing it. It is a very high percentage shot. Usually, takes less time to replace than test and is usually that is what is wrong.
 

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Allante 1989 export running on LPG
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Discussion Starter #10
Do you recommend I get the AC Delco one, I see a local place has a NGK one at around $150, the first one I got was $65. Does anyone have a part number and I can try a search. Things like this are always harder in the UK.
 

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2002 Eldorado Biarritz
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My recommendation is for ACDelco PN - AFS109.

But, if I remember correctly Denso was the actual OE manufacturer. So Denso should be OE as well. I will have to check on that though. I will be in the shop tomorrow and I have a couple sets of exhaust manifolds from that era with OE sensors still in them. I will check to see if they are in fact Denso. But, that Delco number I gave is good if you can get your hands on it over there.
 

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Allante 1989 export running on LPG
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Discussion Starter #12
Thank you, with that part number I have found one in the UK. I will let you know if that fixes it.
 

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Just wanted to add clarification for future readers. The car probably came with an ACDelco manufactured AFS125. In 2000 the Norhtstar received an upgraded engine management system and switched to Denso sensors. AFS109 is a Denso sensor in an ACDelco box and is the part you will receive if you order from the dealership. AFS125 appears to be getting phased out/discontinued and is not readily available. The Denso number is 234-4018.
 

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Allante 1989 export running on LPG
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Discussion Starter #14
UPDATE.
I changed the front oxygen sensor for an AC Delco one, the one I removed rattled like there was a ballbearing inside.
It's early days but it seems to have fixed it, I am going on a 400 mile round trip to Wales tomorrow so that should tel me for sure.
 

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Allante 1989 export running on LPG
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Discussion Starter #16
The engine light has stayed off and the car runs fine but the random stall has come back tenfold. Now every time I stop at the traffic lights it idles fine until the lights change and then stalls, I normally need to press the gas a bit to start it and sometimes it stalls again and sometimes it's fine. No codes.
 

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The engine light has stayed off and the car runs fine but the random stall has come back tenfold. Now every time I stop at the traffic lights it idles fine until the lights change and then stalls, I normally need to press the gas a bit to start it and sometimes it stalls again and sometimes it's fine. No codes.
This is starting to sound like CKPs (crankshaft position sensors). How do fuel trims look. I'd just like to rule out a continuing fuel trim problem especially with the alternative fuel system in place. If fuel trims are normal I'd start leaning towards CKPs. If your scan tool is fast enough you can sometimes catch the glitch by looking at the indicated RPM for the sensors even if the sensors are not coding yet. Not 100% sure the pre-2000's support this PID in the data stream and being an export model it is any ones guess. Also, try checking for codes as soon as the vehicle stalls.
 

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Allante 1989 export running on LPG
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Discussion Starter #18
I have changed the CKPs already at an earlier stage when it was stalling, and it made no difference, I still have the old ones so i could try them again. I will try and clean out the throttle body as that seems to be a popular suggestion, what is the best way to do it?
Also how can I check fuel trims.
 

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I have changed the CKPs already at an earlier stage when it was stalling, and it made no difference, I still have the old ones so i could try them again. I will try and clean out the throttle body as that seems to be a popular suggestion, what is the best way to do it?
Also how can I check fuel trims.
It seemed in earlier posts as though you had access to a scan tool based on some of the things you mentioned. Not sure about export models but over here access to certain parameters is federally mandated. Fuel trim is one of them. Any generic scan tool capable of generating a data stream here will have fuel trims. Usually represented as STFT B1, STFT B2, LTFT B1, LTFT B2 for bank 1 and bank 2 short term and long term fuel trims. A stall on tip in throttle is usually a fuel issue specifically lean. But, CKP failures sometimes manifest this way as well.

A standard test for fuel trims involves looking at fuel trims at idle and and 2000ish rpm cruise. There are more in depth tests to be done involving fuel trim but they would involve having scan tool capable of graphing multiple parameters and saving for view later.

You want to see +- 10% in general at cruise and idle. That is total trim or short and long trims added together but, Northstars tend to run pretty close to zero trim when everything is in order. Also, watch the open or closed loop parameter if a fault is suspected the vehicle will enter open loop and the fuel trim data will be false. Do the check if you can and report back the idle and cruise trims. And the trims around the time of a stall would be very helpful to.

One thing that has crossed my mind is the MAP sensor. The engine relies on the MAF sensor during steady state or higher airflows. But it relies on MAP input for more sudden changes like tip in throttle or hard acceleration. They usually set codes though. If you don't have access to a scan tool anything is going to be a guess. I'd guess MAP sensor first in that case. But, I'm not a fan of guessing.
 
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