P0171 / P0174 (lean codes) pops up but ONLY after refueling!
08-12-19, 03:57 AM
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P0171 / P0174 (lean codes) pops up but ONLY after refueling!
Hi dear RX owners!
Bought our RX300 about 1½ years ago. It's running fine. However, when we bought it, it was low on fuel. We stopped at a gas station and refueled. After leaving, as soon as we got on the highway (next to the gas station) the CEL was lit. We had drove some time from the used cars dealership and we had to pick up our youngest daughter before the staff there went home, so me and my wife had to continue our journey home, with the CEL being on. Once home, I got my OBD2 reader and checked codes. It was showing lean condition on both banks. I had no bad engine vibe or anything though, driving was fine.
Long story short, this has repeated itself ever since that. Oh, I called the dealership and they just said that the car had been unused for a long period of time and now their engine washing might have set something of but it would probably go away if I just gave it time. Since it's an old car and we hadn't payed a fortune and I had no interest in going back and forth between two cities to argue about this I just gave it up. This is a long time ago, so we'll just leave it at that.
Anyways, like I said, it's a recurrent phenomenon, these damn codes. And like I said, it ALWAYS happens after a full refill on gasoline. If I have less than half tank, I can run it for indefinite and the CEL won't come up. I've done visual inspection on the vacuum hoses that can be reached from the hood and everything seems fine. I have cleaned the MAF sensor (which by the way looks to be kind of recently swapped, so I'm thinking previous owner might have struggled with this too, and tried swapping this), all this to no avail.
I've started thinking about the "charcoal canister" is the culprit here. Where is this located on the RX300? Near fuel pump? Is this under rear seat or even under luggage trunk? Speaking of fuel pump, I've also been nosing on the theory that the lean condition is triggered not because of an excessive amount of air, but a non-sufficient amount of fuel. From the fact that it ONLY happens after refueling, I'm thinking the fuel pump itself is probably okay, but since the car has it's fair share of rust under the chassis perhaps corrosion has traveled up to where the fuel pump is dipped down in the fuel tank, causing a corrosion gap either around hose fittings or the big hole for fuel pump, then perhaps this is making "pressure" fall short when the gas tank is full, but sufficient under better conditions (less fuel in the tank). Actually I'm not sure exactly how to explain how my mind goes around this, I'm not really sure about anything.
Gosh, if only someone could point me in the right direction. I don't have the $ to take the car to a garage to do a smoke test to really rule out vacuum line leakage. Also, seeing that both banks are triggered at all times (never just one) I'm concluding that any O2 sensor is unlikely to the culprit here, since these are separate for the two engine banks.
All in all, this is kind of frustrating, I'm a bit eccentric over CEL lights even though it doesn't affect car performance. Could anyone here point me in the right direction?
For example I know "Salim" is some of a guru around here, best hope would be if he felt familiar with the symptom I'm describing!
Bought our RX300 about 1½ years ago. It's running fine. However, when we bought it, it was low on fuel. We stopped at a gas station and refueled. After leaving, as soon as we got on the highway (next to the gas station) the CEL was lit. We had drove some time from the used cars dealership and we had to pick up our youngest daughter before the staff there went home, so me and my wife had to continue our journey home, with the CEL being on. Once home, I got my OBD2 reader and checked codes. It was showing lean condition on both banks. I had no bad engine vibe or anything though, driving was fine.
Long story short, this has repeated itself ever since that. Oh, I called the dealership and they just said that the car had been unused for a long period of time and now their engine washing might have set something of but it would probably go away if I just gave it time. Since it's an old car and we hadn't payed a fortune and I had no interest in going back and forth between two cities to argue about this I just gave it up. This is a long time ago, so we'll just leave it at that.
Anyways, like I said, it's a recurrent phenomenon, these damn codes. And like I said, it ALWAYS happens after a full refill on gasoline. If I have less than half tank, I can run it for indefinite and the CEL won't come up. I've done visual inspection on the vacuum hoses that can be reached from the hood and everything seems fine. I have cleaned the MAF sensor (which by the way looks to be kind of recently swapped, so I'm thinking previous owner might have struggled with this too, and tried swapping this), all this to no avail.
I've started thinking about the "charcoal canister" is the culprit here. Where is this located on the RX300? Near fuel pump? Is this under rear seat or even under luggage trunk? Speaking of fuel pump, I've also been nosing on the theory that the lean condition is triggered not because of an excessive amount of air, but a non-sufficient amount of fuel. From the fact that it ONLY happens after refueling, I'm thinking the fuel pump itself is probably okay, but since the car has it's fair share of rust under the chassis perhaps corrosion has traveled up to where the fuel pump is dipped down in the fuel tank, causing a corrosion gap either around hose fittings or the big hole for fuel pump, then perhaps this is making "pressure" fall short when the gas tank is full, but sufficient under better conditions (less fuel in the tank). Actually I'm not sure exactly how to explain how my mind goes around this, I'm not really sure about anything.
Gosh, if only someone could point me in the right direction. I don't have the $ to take the car to a garage to do a smoke test to really rule out vacuum line leakage. Also, seeing that both banks are triggered at all times (never just one) I'm concluding that any O2 sensor is unlikely to the culprit here, since these are separate for the two engine banks.
All in all, this is kind of frustrating, I'm a bit eccentric over CEL lights even though it doesn't affect car performance. Could anyone here point me in the right direction?
For example I know "Salim" is some of a guru around here, best hope would be if he felt familiar with the symptom I'm describing!
08-12-19, 04:02 AM
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As a final note, since I have never gotten any misfire codes, I've kind of ruled out the possibility of one or several bad fuel injector(s).
Simply put, I'm putting all my focus on the fact that the codes pops up only after filling up the tank, since this seems to be the leitmotif.
Simply put, I'm putting all my focus on the fact that the codes pops up only after filling up the tank, since this seems to be the leitmotif.
08-14-19, 06:46 PM
#4
The canister and related hoses and valves could play a role. Google for "rx300 emission control (EC) pdf"
08-20-19, 08:22 AM
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I also did find a copy of the Emissions control PDF which you recommended, excellent. I also found this old thread covering the whereabouts of the charcoal canister. Interesting indeed, I think ~90% of this forum is from the US, whilst I'm actually from the EU. If you compare the gas tank blueprint from EU versus US models (links below) you'll see that the canister is indeed close to the gas tank itself on the US market cars, while RX300 made for the European market (like mine) seems to have it someplace between the firewall and the air filter box.
2001 EU RX300 http://japan-parts.eu/lexus/eu/2001/...k-tube/2#77740
2001 US RX300 http://japan-parts.eu/lexus/us/2001/...k-tube/2#77740
I will definitely inspect this thoroughly in the upcoming days. As I probably need to remove the air filter housing to visually inspect the charcoal canister I think I'll be too lazy to do it today.
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