Full Powertrain, Subframe & Suspension Removal on the Free Hyundai Sonata - Part II
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Date: 2025-10-11
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Comments and reviews: 20
Togrul_avtoblog
Hello, my friend. Greetings from the Land of Fire Azerbaijan, from Baku, the home of Formula 1!
I’m facing an unusual issue and would really appreciate your help.
Vehicle: Kia Optima 2. 0T GDI (2012)
DTC: P0091 Fuel Pressure Regulator Control Circuit Low
The fault code appears only during cranking (starter engaged.
When the ignition is in ACC/ON position or when the engine is running, the code does not appear.
The in-tank fuel pump delivers 3. 5 bar pressure and holds it steady.
The GDI high-pressure pump wiring is intact.
When the ignition is switched ON, there is a momentary 12V priming voltage at the GDI pump connector, which then cuts off so the PCM is functioning and recognizing this stage correctly.
I also tested with a brand-new GDI pump, same result.
The camshaft and its position sensor are fine.
During cranking, the battery voltage drops to 10. 5V, which is within normal limits.
The fuel pressure regulator control circuit was tested under load wiring is good.
The GDI pump provides the required fuel pressure during cranking, as commanded by the PCM.
However, during cranking, when the DTC sets, I checked the control signal with an oscilloscope there are no pulses coming from the PCM to the regulator valve.
Still, when the ignition is ON (without cranking, the PCM sends and then cuts 12V as expected, meaning it sees the circuit and reacts normally.
The PCM itself has been tested and confirmed good.
So my question is:
Why does this P0091 code appear only while cranking, even though everything tests normal otherwise
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Hello, my friend. Greetings from the Land of Fire Azerbaijan, from Baku, the home of Formula 1!
I’m facing an unusual issue and would really appreciate your help.
Vehicle: Kia Optima 2. 0T GDI (2012)
DTC: P0091 Fuel Pressure Regulator Control Circuit Low
The fault code appears only during cranking (starter engaged.
When the ignition is in ACC/ON position or when the engine is running, the code does not appear.
The in-tank fuel pump delivers 3. 5 bar pressure and holds it steady.
The GDI high-pressure pump wiring is intact.
When the ignition is switched ON, there is a momentary 12V priming voltage at the GDI pump connector, which then cuts off so the PCM is functioning and recognizing this stage correctly.
I also tested with a brand-new GDI pump, same result.
The camshaft and its position sensor are fine.
During cranking, the battery voltage drops to 10. 5V, which is within normal limits.
The fuel pressure regulator control circuit was tested under load wiring is good.
The GDI pump provides the required fuel pressure during cranking, as commanded by the PCM.
However, during cranking, when the DTC sets, I checked the control signal with an oscilloscope there are no pulses coming from the PCM to the regulator valve.
Still, when the ignition is ON (without cranking, the PCM sends and then cuts 12V as expected, meaning it sees the circuit and reacts normally.
The PCM itself has been tested and confirmed good.
So my question is:
Why does this P0091 code appear only while cranking, even though everything tests normal otherwise
reply
TimfromAlabama
Yeah, we southerners don't have the rust issue you guys do. HOWEVER, I bought a used 2019 Silverado LT Crew Trailboss LOADED with everything including a spray in liner and even a hard, folding tonneau cover that came from Detroit, so I'm about to go get the underside fixed up. It doesn't have but a tiny amount of rust, as the guy who originally owned it kept it garaged. Only had 52, 000 miles on it. Will be removing the AFM/DFM junk, and that irritating start/stop system here real soon. All in all, not bad for what we paid for it. Might be looking into the stuff you use to undercoat vehicles, or something to undercoat it so any of the tiny spots of surface rust don't become an issue, ever. SO, I say all this to say, come down south and live a year and work on cars and you'll think you were on a year long vacation after what you deal with up there. lol. Looking forward to seeing the entire build on this car and to see and hear it run and drive. Sounds like a good deal for your kid. Oh, from my first ever car, a 1960 Buick LeSaber when I was 16, to 4 years into being married at 24, never had a car or truck with a/c. Never had a/c in my grandparents or parents vehicles growing up, not even in their houses. 24 years without and I lived, so if the a/c doesn't work, up that way, yall will survive. AND, say Hello to Mrs O, to Luna. and the cricket. LOL
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Yeah, we southerners don't have the rust issue you guys do. HOWEVER, I bought a used 2019 Silverado LT Crew Trailboss LOADED with everything including a spray in liner and even a hard, folding tonneau cover that came from Detroit, so I'm about to go get the underside fixed up. It doesn't have but a tiny amount of rust, as the guy who originally owned it kept it garaged. Only had 52, 000 miles on it. Will be removing the AFM/DFM junk, and that irritating start/stop system here real soon. All in all, not bad for what we paid for it. Might be looking into the stuff you use to undercoat vehicles, or something to undercoat it so any of the tiny spots of surface rust don't become an issue, ever. SO, I say all this to say, come down south and live a year and work on cars and you'll think you were on a year long vacation after what you deal with up there. lol. Looking forward to seeing the entire build on this car and to see and hear it run and drive. Sounds like a good deal for your kid. Oh, from my first ever car, a 1960 Buick LeSaber when I was 16, to 4 years into being married at 24, never had a car or truck with a/c. Never had a/c in my grandparents or parents vehicles growing up, not even in their houses. 24 years without and I lived, so if the a/c doesn't work, up that way, yall will survive. AND, say Hello to Mrs O, to Luna. and the cricket. LOL
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whatdoyouthinktodd
All three of my kids I bought them their first car and I paid for their insurance. My oldest is 30 years old with two kids her husband is a sergeant in the military. My second child the middle child is in her last year of law school. Sh6 is still driving her car from high school. My last child is still driving his car from high school. Finishing up college and working part-time.
I paid for the car and the insurance. But I don't pay for the schooling that's on them. My oldest student loans are paid for. The middle kid her tuition for u of m is paid for. Law school she'll pay for it when she gets out. The youngest is working on paying his tuition he is around 3/4 of the way through it. Not all kids grow up to be pricks. You know most of that is a parent's shoulders. Teach your kids morals and values and how to use money correctly. They turn out okay.
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All three of my kids I bought them their first car and I paid for their insurance. My oldest is 30 years old with two kids her husband is a sergeant in the military. My second child the middle child is in her last year of law school. Sh6 is still driving her car from high school. My last child is still driving his car from high school. Finishing up college and working part-time.
I paid for the car and the insurance. But I don't pay for the schooling that's on them. My oldest student loans are paid for. The middle kid her tuition for u of m is paid for. Law school she'll pay for it when she gets out. The youngest is working on paying his tuition he is around 3/4 of the way through it. Not all kids grow up to be pricks. You know most of that is a parent's shoulders. Teach your kids morals and values and how to use money correctly. They turn out okay.
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scotts4125
I went about it a little differently. My son earned a scholarship to college. He didn't really need a car. Every break they had and summer he worked for a friend's father in the shipping dept. He bought clothes and had some fun money. They live close by so we would drop him off at their house and they would drive him in. My son earned 2 majors graduated Summa Cum Laude, honors and made Phi Beta Kappa. With that he earned a scholarship to the best law school in the state. At 22 as a reward for all his hard work I bought him a brand new car. I didn't want to take a chance on him having issues plus he earned it. Not many kids wait until they are 22 for their first car. Poor kid now is either in class or in the law library to the wee hours. I taught him hard work pays off or at least i think I did.
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I went about it a little differently. My son earned a scholarship to college. He didn't really need a car. Every break they had and summer he worked for a friend's father in the shipping dept. He bought clothes and had some fun money. They live close by so we would drop him off at their house and they would drive him in. My son earned 2 majors graduated Summa Cum Laude, honors and made Phi Beta Kappa. With that he earned a scholarship to the best law school in the state. At 22 as a reward for all his hard work I bought him a brand new car. I didn't want to take a chance on him having issues plus he earned it. Not many kids wait until they are 22 for their first car. Poor kid now is either in class or in the law library to the wee hours. I taught him hard work pays off or at least i think I did.
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patrickbennett9120
Yes our kids must pay their bills and get their own insurance. my oldest tried the con of put me on your insurance and I will pay you. no way Jose. also I did gift him a car but he had transfer the title (not a completely easy process in the PRNY) to his name as well. that saves me from getting sued if crashes out and a lawyer see's my name on the title. protect yourself never let someone driver your car with your name still on it. lawyers go for who has the money. Eric I agree if you give everthing to your kids they become entitled and that is not good for them. or you in the long run. when my kids need money for something I always make them work for it. even if the work is trivial. it's the process that is important.
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Yes our kids must pay their bills and get their own insurance. my oldest tried the con of put me on your insurance and I will pay you. no way Jose. also I did gift him a car but he had transfer the title (not a completely easy process in the PRNY) to his name as well. that saves me from getting sued if crashes out and a lawyer see's my name on the title. protect yourself never let someone driver your car with your name still on it. lawyers go for who has the money. Eric I agree if you give everthing to your kids they become entitled and that is not good for them. or you in the long run. when my kids need money for something I always make them work for it. even if the work is trivial. it's the process that is important.
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smarthome2660
NGL, I was a little concerned about the rear of the car being too heavy, once the 1, 000lbs engine was removed. I have seen cars fall off lifts at that point. Maybe consider strapping the front to the lift when you drop the car onto the new engine assembly. If you lower the car on down, and something hangs up, it could topple the car.
Good parents teach kids to be self sufficient, and not just buy them cars. One of my sisters has eight kids, and she bought all of them their first cars. She has not taught them to be adults, and she is still helping them well in to their late thirties. My oldest brother has four kids, and did the same, and is still buying them cars for up to the fourth time. His kids are in their forties.
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NGL, I was a little concerned about the rear of the car being too heavy, once the 1, 000lbs engine was removed. I have seen cars fall off lifts at that point. Maybe consider strapping the front to the lift when you drop the car onto the new engine assembly. If you lower the car on down, and something hangs up, it could topple the car.
Good parents teach kids to be self sufficient, and not just buy them cars. One of my sisters has eight kids, and she bought all of them their first cars. She has not taught them to be adults, and she is still helping them well in to their late thirties. My oldest brother has four kids, and did the same, and is still buying them cars for up to the fourth time. His kids are in their forties.
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autorepair
Eric cracked me up talking about no rust southern vehicles. I live in the south; I have a 07 F-150 that I bought new in 07. During oil changes I do a complete undercarriage inspection. There is zero rust, zero leaks and the OEM stickers are still applied and readable. The only rust problem I have encountered was a buildup on the wheel speed sensors. This was caused by the raw unpainted / non plated OEM brake rotors rusting. I splurged on new OEM wheel speed sensors, plated cut and drilled rotors and powder coated OEM calipers. So far, that has been the only problem aside from replacing batteries and tires. Good truck! I grew up in the rust belt and never imagined how long a vehicle will last without snow, ice and salt!
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Eric cracked me up talking about no rust southern vehicles. I live in the south; I have a 07 F-150 that I bought new in 07. During oil changes I do a complete undercarriage inspection. There is zero rust, zero leaks and the OEM stickers are still applied and readable. The only rust problem I have encountered was a buildup on the wheel speed sensors. This was caused by the raw unpainted / non plated OEM brake rotors rusting. I splurged on new OEM wheel speed sensors, plated cut and drilled rotors and powder coated OEM calipers. So far, that has been the only problem aside from replacing batteries and tires. Good truck! I grew up in the rust belt and never imagined how long a vehicle will last without snow, ice and salt!
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donald4416
Well Eric, in watching this video of Hyundai engine swap, I just did Sub-frame on 2010 Hyundai sonata at 148, 000 miles that was rusted pretty good on right front 15 from front subframe bushing to cvc chaft area, That subframe change wasn't fun without car lift but with jack stands 3- ton type and 2- 3- ton floor jacks i - got it swaped out with good clean subframe from doner car I'm in lorain, ohio, I did this subframe change all by- myself No Help at all took me 3- weeks cause Steering rack line high pressure line was pita to fix it has both ends with rubber 0- rings, that line cost 150. 00 So i had fix it myself. Almost done with this car frame work, So yes as you say Eric (You can Do It)
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Well Eric, in watching this video of Hyundai engine swap, I just did Sub-frame on 2010 Hyundai sonata at 148, 000 miles that was rusted pretty good on right front 15 from front subframe bushing to cvc chaft area, That subframe change wasn't fun without car lift but with jack stands 3- ton type and 2- 3- ton floor jacks i - got it swaped out with good clean subframe from doner car I'm in lorain, ohio, I did this subframe change all by- myself No Help at all took me 3- weeks cause Steering rack line high pressure line was pita to fix it has both ends with rubber 0- rings, that line cost 150. 00 So i had fix it myself. Almost done with this car frame work, So yes as you say Eric (You can Do It)
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PistonSlapper
As a former Kia/Hyundai/Genesis tech, it’s always fun watching people do their first powertrain replacements on these. All the little tricks and techniques of the process, finding each one and the little aha moments after you’ve found them are like little lottery wins. It’s awesome to see you do this for your son. There’s a lot of little quirks once you get it running again (assuming the new to you assembly doesn’t have the issues already) but worth the investment you just made for your sons future endeavors. I doubt I’m the only one in your viewership that has worked on these specifically at the dealer level but if need some questions answered, I got some answers! Cheers
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As a former Kia/Hyundai/Genesis tech, it’s always fun watching people do their first powertrain replacements on these. All the little tricks and techniques of the process, finding each one and the little aha moments after you’ve found them are like little lottery wins. It’s awesome to see you do this for your son. There’s a lot of little quirks once you get it running again (assuming the new to you assembly doesn’t have the issues already) but worth the investment you just made for your sons future endeavors. I doubt I’m the only one in your viewership that has worked on these specifically at the dealer level but if need some questions answered, I got some answers! Cheers
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bigmikepimp2003
Im a mechanic in Huntington Beach California and one day i had a guy show up in a Lincoln Navigator from Pennsylvania. And his knucle lower control arm and all the suspension in the passenger side was falling apart. And he was gonna vacation here and he was driving back. So i had to do the entire job with a tourch and on the alignment rack cuz i felt if i did it on a 2 post lift it was gonna snap the truck in half and it was horrible no bolt would come off used pb blaster the tourch and a sht ton of curse words to do the job. I dont know how yall work that way it takes twice the time the book calls for yall lose money
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Im a mechanic in Huntington Beach California and one day i had a guy show up in a Lincoln Navigator from Pennsylvania. And his knucle lower control arm and all the suspension in the passenger side was falling apart. And he was gonna vacation here and he was driving back. So i had to do the entire job with a tourch and on the alignment rack cuz i felt if i did it on a 2 post lift it was gonna snap the truck in half and it was horrible no bolt would come off used pb blaster the tourch and a sht ton of curse words to do the job. I dont know how yall work that way it takes twice the time the book calls for yall lose money
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Heyyo_Friday
So down here in the peoples republic of texas. We had 03 car from Mass. Clearly had spent some up there because she was about 3 more winters away from being wilberts material.
Anywho. That same car a tech who has never worked a northern car, turned and oil pan reseal job into a full exhaust. We told him multiple times to not touch the underfloor converter bolts and just unhook the exhaust from the manifolds (fwd hondoo v6. He did it anyways. Ended up putting on $3500 in exhaust on the car.
So in conclusion. We dont cuss at rust. We make everything way harder than it needs to be
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So down here in the peoples republic of texas. We had 03 car from Mass. Clearly had spent some up there because she was about 3 more winters away from being wilberts material.
Anywho. That same car a tech who has never worked a northern car, turned and oil pan reseal job into a full exhaust. We told him multiple times to not touch the underfloor converter bolts and just unhook the exhaust from the manifolds (fwd hondoo v6. He did it anyways. Ended up putting on $3500 in exhaust on the car.
So in conclusion. We dont cuss at rust. We make everything way harder than it needs to be
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myk55501
The other thing is the valve cover gasket leaks around the spark plug tubes you got to replace the gasket don't use a Hyundai I use a the blue gasket one that's what we used to call it the other thing on that motor is the crankshaft sensor and the camshaft sensor OEM only I would pull them out and check them and clean them and just test them real quick before you put the motor back in oh and the other thing is you can only use Hyundai transmission fluid Hyundai certain model engines in cars you'll damage the transmission if you use somebody else's fluid
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The other thing is the valve cover gasket leaks around the spark plug tubes you got to replace the gasket don't use a Hyundai I use a the blue gasket one that's what we used to call it the other thing on that motor is the crankshaft sensor and the camshaft sensor OEM only I would pull them out and check them and clean them and just test them real quick before you put the motor back in oh and the other thing is you can only use Hyundai transmission fluid Hyundai certain model engines in cars you'll damage the transmission if you use somebody else's fluid
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TheRealMikeWilly
12: 49. Oregonian here, 15 years turning wrench professionally, grew up in an independent shop, went to turn wrench for a big dealership and hated it, now I run my own shop. Can confirm that what we get mad about is all you rust belters bringing us your, as you called em, rotboxes but the icing on the cake is when they're not understanding why we're telling you that your subframe is literally crumbling to bits and I got more of it in my eyes than remains on the vehicle and it needs to be replaced to the tune of a couple grand.
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12: 49. Oregonian here, 15 years turning wrench professionally, grew up in an independent shop, went to turn wrench for a big dealership and hated it, now I run my own shop. Can confirm that what we get mad about is all you rust belters bringing us your, as you called em, rotboxes but the icing on the cake is when they're not understanding why we're telling you that your subframe is literally crumbling to bits and I got more of it in my eyes than remains on the vehicle and it needs to be replaced to the tune of a couple grand.
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johnr6841
Just lived the opposite 2012 Mazda CX-9 NY car, AKA rot-box, and I have had it in SC for a few years as transportation at a vacation home. It developed a leak at the rear diff. Took it to 3 shops and they all said 'we ain't touchin that'. It was so rusted they were not at all willing to even attempt a repair. Sadly it's gone now because the rust was just too much to deal with. 13 years and it owed me nothing but if it could have been repaired easily I'd still have it. Was a great vehicle, while it lasted.
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Just lived the opposite 2012 Mazda CX-9 NY car, AKA rot-box, and I have had it in SC for a few years as transportation at a vacation home. It developed a leak at the rear diff. Took it to 3 shops and they all said 'we ain't touchin that'. It was so rusted they were not at all willing to even attempt a repair. Sadly it's gone now because the rust was just too much to deal with. 13 years and it owed me nothing but if it could have been repaired easily I'd still have it. Was a great vehicle, while it lasted.
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WreckDiver99
$5K Can't even get a rusted out chevy here for that. Not even close. A feller saw one just the other day (as I may need another car soon. $7500, says right on it Needs Trans, Needs Engine. Yea. $7500 for a car that needs. That much in work. OH. and it needed tires, windshield, drinker side mirror. Insurance around here I'm 57, no tickets, no accidents, multi-car, multi-product, long term customer. and that insurance is $1800/year (or more. Registration $400. Yea. Michigan SUCKS for insurance.
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$5K Can't even get a rusted out chevy here for that. Not even close. A feller saw one just the other day (as I may need another car soon. $7500, says right on it Needs Trans, Needs Engine. Yea. $7500 for a car that needs. That much in work. OH. and it needed tires, windshield, drinker side mirror. Insurance around here I'm 57, no tickets, no accidents, multi-car, multi-product, long term customer. and that insurance is $1800/year (or more. Registration $400. Yea. Michigan SUCKS for insurance.
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ShannonCoffey-l6b
I had a deal with two of my kids that I they had to pay half the cost of a new car and I would pay the rest. They did that with job money they saved up by the time they were 16. They drove those cars the last two years of HS and through their master degrees some 10 years later. My one kid sold his car back to me for half value when he got married and bought a new car. It worked out great. They had reliable cars and did not have to worry about car payments all the way through school.
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I had a deal with two of my kids that I they had to pay half the cost of a new car and I would pay the rest. They did that with job money they saved up by the time they were 16. They drove those cars the last two years of HS and through their master degrees some 10 years later. My one kid sold his car back to me for half value when he got married and bought a new car. It worked out great. They had reliable cars and did not have to worry about car payments all the way through school.
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HansJansen-q7l
I did something similar with a 2006 Explorer given to me by my brother. When he went to trade it in for his new Escape Hybrid, they offered him $350, and said I know someone that could benefit more from it then that ( he had just replaced all four tires with new ones. His intent was for me to swap the tires on my 2010 Explorer (same generation) and scrap the rest. Instead I made it road worthy, certified it and my son has been driving it to work for a year. Cost About $3000.
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I did something similar with a 2006 Explorer given to me by my brother. When he went to trade it in for his new Escape Hybrid, they offered him $350, and said I know someone that could benefit more from it then that ( he had just replaced all four tires with new ones. His intent was for me to swap the tires on my 2010 Explorer (same generation) and scrap the rest. Instead I made it road worthy, certified it and my son has been driving it to work for a year. Cost About $3000.
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SLC-e7z
My 19 yo grandson came by with his friend and friend's car for me to scan for codes. So sorry for the kid. He got fleeced for $750 for a 2002 Century that needed a CAT, windshield wipers and horn did not work two windows would not go down and needed a muffler. Poor kid who had no money was sleeping on my daughter's (grandson's) couch because his parents did not give a shit about him. All kids need to get experience wrenching on a few cars as they grow up.
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My 19 yo grandson came by with his friend and friend's car for me to scan for codes. So sorry for the kid. He got fleeced for $750 for a 2002 Century that needed a CAT, windshield wipers and horn did not work two windows would not go down and needed a muffler. Poor kid who had no money was sleeping on my daughter's (grandson's) couch because his parents did not give a shit about him. All kids need to get experience wrenching on a few cars as they grow up.
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CrimeVid
I read all these comments about peoples dads teaching them mechanicery, My dad knew nothing about it and was less than interested, but was an inspired buyer of good second, hand cars, I don't think he ever had one that lasted him less than ten years, with the amount of maintenance you'd expect, one yearly service if he remembered. The first three were inline sixes. I followed in his footsteps, I've had my present car twenty years!
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I read all these comments about peoples dads teaching them mechanicery, My dad knew nothing about it and was less than interested, but was an inspired buyer of good second, hand cars, I don't think he ever had one that lasted him less than ten years, with the amount of maintenance you'd expect, one yearly service if he remembered. The first three were inline sixes. I followed in his footsteps, I've had my present car twenty years!
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darreng745
We make our kids pay for their own insurance so they don t grow up to be a bunch of self entitled little pricks Some might say oh that is so wrong, but how about they learn that there is no such thing as a free lunch that early Money has value and it is not going to be wasted on you for your entire life so the sooner they understand that concept and deal with it means they are more likely to be reponsible with their finances.
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We make our kids pay for their own insurance so they don t grow up to be a bunch of self entitled little pricks Some might say oh that is so wrong, but how about they learn that there is no such thing as a free lunch that early Money has value and it is not going to be wasted on you for your entire life so the sooner they understand that concept and deal with it means they are more likely to be reponsible with their finances.
reply
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