Please note, I'm not car savvy nor can I really fix stuff myself when it comes to cars.

2008 Volvo S40 with 215,500 miles. Our check engine light came on 9/25/22. My wife who usually doesn't get gas, filled it up two days before on 9/23/22. Thinking it was weird timing and that perhaps she didn't screw the gas cap on well enough, I tightened the gas cap on correctly after it seemed loose/not screwed on right. This was done on 9/25/22. After doing this with the CEL still on, I took it to Autozone to get the codes read. The rep showed me that no fault codes came up which we both found odd. He ended up clearing out the CEL for me. The CEL never came back on again and made me suspect it was from the gas cap not being tied on correctly. The CEL finally came back on again on 11/10/22. On 11/12/22, I rescrewed the gas cap on again like last time but it didn't seem as off as the previous time. After doing this with the CEL still on, I took it to Autozone to try and read the code. This time it did come up with a code, P0190 - Fuel Rail Pressure Sensor. The rep did not clear out the code this time so we left and went somewhere else where I turned off the car for the first time since messing with the gas cap earlier that day. When we left an hour later and started the car back up, the CEL was gone and still currently is gone.

Back in 9/2021, we had a check engine light issue come up showing a code for leak detection pump which we then fixed. But then a code relating to a faulty leak detection pump came up again in 8/2022, so my shop luckily replaced it again for free. But my point in describing this event too is wondering if there was all along nothing wrong with a leak detection pump as well and if it was from a messed up gas cap or something? Maybe not though and two different issues. I just want advice on how to proceed going forward with this new latest problem because I'm really confused on what to do next to solve this. My shop usually won't be able to help if no CEL is on but I can't guarantee when it comes on/off or if this could be just something relating to a gas cap. Pure speculation on my part though and I'm probably wrong, the timing and events just seem weird.

Sidenote, next week I was hoping to drive 6 hours round trip for the holidays but not sure if this issue is one to reconsider doing that until this problem is fixed? We don't think we've noticed any different driving/mechanical issues but always hard to know.

Thanks in advance!

 

you'd need to know what the code was that led the original shop to replace the pump in the first place. To you question about a loose gas cap, the background is part of the emissions system is the evap system which is designed to take gasoline vapors out of the tank and pull them into the intake where the fuel vapors get burned. This requires a sealed system so the pump pulls a vacuum to make sure everything is tight - otherwise a code will be set. Things that typically fail include the purge valve (a vacuum controlled solenoid up front by the drivers's side headlight), a tear in the hose that runs from the purge valve all the way back to the charcoal canister in front of the gas tank, the canister, the gas cap seal and the pump. Knowing the exact codes is what gives the tech a clue as to what tests to run - ie a small evap leak may point them to test the purge valve or check the vacuum line, a large evap leak code may point them to the charcoal canister. electrical devices like a pump may set their own fault codes as well. With all that said, your code for the fuel pressure sensor is saying the sensor signal was not what the ECU was expecting. Could be the sensor, could be the fuel pump, a fuel pick up, a vaccuum leak. So a DIY person would simply drop in a new sensor hoping that the 80/20 rule works in their favor, but a sensible tech would put a pressure gauge on the fuel rail to see if the sensor is reporting the same pressure that the mechnical gauge is reporting then move on to the next test such checking the fuel pump's control signals via a fully featured scan tool.

 

Thank you for your reply and for your help! Unfortunately since I'm not a car guy, a lot of that went over my head but that's ok lol! Just another update. The check engine light has been off since my last post but it came back on 12/8/22 at 216,859 miles. On 12/11, I rescrewed the gas cap on and took it to Autozone with the CEL still on. The code again read P0190 - Fuel Rail Pressure Sensor. They didn't clear out the CEL and the next day on 12/12 as my wife was headed to work, she noticed the CEL was gone.

I'm just kinda stumped on how to proceed. Why does this CEL keep coming back on and off and why did it not throw a code the first time but it has the last two times? And there seems to possibly be a relation with the gas cap or not necessarily? I'm due for an oil change in roughly 1000 miles but I'm afraid the CEL won't be on when I take it to my mechanic and can he address the issue without it being on? How serious does this issue sound in general? Like do you think I'm ok still driving with this CEL coming off and on until I can see my mechanic? Whether it's related or not just wanted to re-mention that back in 9/2021, we had a check engine light issue come up showing a code for leak detection pump which we then fixed but that came up with different codes like P2402 and P043E at the time. But then a code relating to a faulty leak detection pump came up again in 8/2022, so my shop luckily replaced it again for free.

 

CELs are there to alert you to issues that either create emissions problems or conditions that if unchecked could damage the engine. Some of the codes are averaging (ie data is accumulated over time) others are more immediate (say a sensor signal is missing) are allowed to clear the lamp if the condition goes away. In most cases even if the lamp turns off, the fault code is still stored in the computer. So take for example if the fuel pressure sensor reports fuel pressure that is above or below an expected threshold, the code is set. Now lets say the fuel pressure returns to the normal range for the measuring window. The light could go off but the fault is still stored. Its up to the mechanic to use that information to triage and determine root cause. For example, say the fuel pump is worn and when it heats up it loses its pumping capacity... You could imagine that the fuel pressure would vary based on driving conditions and create intermittant CELs. The mechanic will use the fault code as a starting point to determine what other tests need to be done such as measuring the pressure with a mechanical guage and compare to what the sending unit is telling the computer. As to the gas cap - that is a possible cause for an evap system leak. So cap off, code and CEL gets set. Cap goes on, car will no longer report an evap leak so for most models the code will self clear or turn off the lamp. There are some common codes associated with a loose gas cap like a P0457 or a P0455 which is different from other evap codes for say the purge valve or the leak detection pump. In your case, the P2402 is saying the leak detection pump control circuit signal is returning a high voltage value. This could mean the pump motor is drawing too much current (like a worn out motor), or the connectors or relay have corroded connections creating resistance, there's wiring issues etc. A bad pump motor is only one possible cause so the tech needs to do a bit more investigating. Same thing with the P043E. that is saying the evap system's pressure sensor is not returning an expected value. Could be the pump, could be a clogged orifice, could be an electrical connection issue, could be a failed charcoal canister. Again further testing would be required but if both a 2402 and a 043E show up at the same time, it would make sense to resolve the common issue - which is the pump and its associated circuits.

 

Thanks for your help and reply again! That helps makes a little bit of sense. Just another update, the check engine light came back on 12/27/22 at 217,745 miles. I've been tired of going to Autozone to get the codes read so I didn't do it for this last one since I figured it is probably going to show the same code and because I'm going to be visiting my mechanic soon anyways for oil change, etc. The light has still been on since 12/27/22 so this is also the longest it's stayed on. If I can't get in to see my mechanic for the next 1-3 weeks, do you think I'm still ok driving it with this ongoing issue? With the check engine light coming off and on intermittently since 9/25/22?

 

most CEL codes are emissions related - but its always helpful to know the exact code. One other option is to buy a cheap Centec or Autel code reader from Harbor Freight or Amazon etc and keep it in the car. I paid about $30 for one and it works fine on my son's 2000 S40 as well as our Highlander and VW CC. There are also small bluetooth scanners that link up to a smart phone for $20 or so.

 

I’m having the exact same issue right now. What came of this ?

 

xtcy90, did you read your codes as well? if so, which ones are coming up? This old thread started by asking about codes related to the evap system - which is intended to pull gas tank vapors into the intake to be burned. The evap system has several components which can fail, which is where you'd need to know which code(s) are being set to plan your diagnostics. To note, the general design is that the fuel tank is connected to a charcoal cannister that captures the vapors. there's then a line that runs from the cannister (near the fuel tank) to the front of the car where there's a purge valve. As part of the system there's also a evap leak detection pump which pressurizes the system to allow the sensors to detect a leak (this is where the gas cap comes into play - if the gas cap is removed or has a bad seal, the diagnostics will sense the low pressure and set a code). The most common failures are torn vacuum/vent lines or a bad purge valve. Purge valves are easy to replace (up on the grill by the driver's side headlight) but finding a tear in a vent line often takes a smoke test to find.

Here's a great write up of how this system works.

https://www.nyvip.org/PublicSite/OBD...%20the%201970s.

 

This requires a sealed system so the pump pulls a vacuum to make sure everything is tight - otherwise a code will be set. Things that typically fail include the purge valve (a vacuum controlled solenoid up front by the drivers's side headlight), a tear in the hose that runs from the purge valve all the way back to the charcoal canister in front of the gas tank, the canister, the gas cap seal and the pump.