355 P1448, Rattle from Bypass?

Hello all,


Sorry for a bit late response on this topic but reading this thread and 3-4 others on Ferrchat made me to write this up not to response to particular people but as a general overview and troubleshooting steps for the Error Code P1448 as I see the responses in the above one person or another uses a general logic without understanding of how the system works and how to troubleshoot it (no offends, please). We all are here to help.


My case is I had a P1448 error code 5 years ago after I purchased the car and the local dealership advised to change the 1-way valves in the air injection system and they showed the dinging sound the valve makes when it dies so the new valves were good for 3 years or so then the code came up again and I replaced one or both valves and the code came up again later last Fall and I ordered a new valve because the other one seemed still OK - and that was the time when the real issue started...


So, in my case after about 3-4 weekends the code came up. I was surprised, ordered a new valve and then the Winter came so the task rolled over to Spring 2019 like end March or April when I pulled the 355 to the new driving season. The long story short I replaced 4 (four) valves and came to the observation it might be something else as less likely 4 valves in a row become defective so quickly while they should like about 3 years or so.


Therefore, I will skip the part of trying this and that following other's advises and I came to the point of the need of understanding this system and knowing how the system works established the steps in below a someone needs to follow.


So, if you get an error code P1448 it means a number of components of the Air Injection OR bypass valve system is failed. It's not like one person on this thread said: "if you get P1448- it's the thermo-couple". Or so forth.


1. Here where you start. The theory. It's described in the F355 Workshop Manual, Vol. 1 on pp. C38-C45. The bridged version is this:

The air injection system blows fresh air in both cats when:

-the coolant is not warmed-up from 19F to 145F.

-during cats warm-up

-when the oxygen sensor(s) are disconnected or defective


The bypass valve (US cars) is operated by Motronic ECU taking the reading from the 3-rd thermo-couple that is located in the middle in front of the bypass valve. When the temperature of the exhaust gases gets too hot, Motronic opens up the bypass valve. It's not because of the high RPM or rapid acceleration whatsoever per say as some people say. It's when it is too hot so the cats can get damaged. So the P1448 code comes up when anything is wrong with either of these 2 systems.


Troubleshooting steps:


So here where you start. The bypass valve system uses the vacuum lines shared with the air injection system so you start with it first.


1. The air injection system takes the vacuum from both banks of the engine you will see the vacuum hoses coming out from the both rear upper parts of the engine, merged by a T-coupler and going around RH air filter box to the air injection device. Under beneath of the RH fabric tube which is going to the RH air filter there is a white plastic connector which connects the vacuum hose coming from the engine with a hose which is going to the vacuum reservoir (a big black polished cylinder between the RL wheel and the rear bumper. Disconnect that connector, start the engine, and check if any vacuum is sucking on the hose which is coming from the engine. If there is vacuum, you good. If not, here is what your issue is. The vacuum hoses can get old, cracked, and whatsoever. If there is no vacuum, both air injection nor bypass valve systems will not work = P1448 error code.


2. If the vacuum is present on the hose coming from the engine, proceed. Connect the hoses back to the connector and disconnect the hose which is going OUT from the vacuum reservoir. Start the engine and check with your finger if the vacuum is present in the reservoir. If yes, proceed to the next step. If not, here is your problem. A reservoir can get rusted through on the body, nipples, whatsoever.


3. If your reservoir is good, disconnect the INBOUND hose from it and connect it to the nipple which going to the bypass valve. The nipple is located just below the connector for the hose which is coming from the engine. Start your engine. If your bypass valve opens and stays open, it's good. If it remained closed, remove the RH air filter box and there is a rubber hose from the bypass valve to the thin copper line you just plugged in the hose borrowed from the vacuum reservoir. The bypass valve hose has 2 clamps on both ends, due to high temperature from the muffler, the chances are the clamps can cut into the rubber, etc. If you start the engine and bypass valve opens up, proceed to the next step. If not, if there is no issue with the rubber hose, the bypass valve can get a membrane rusted through, or etc. So that's your issue. If your bypass is good and opens up, go to the next step.


4. Connect the hose that you unplugged from the vacuum reservoir back and the hose which you disconnected from the nipple of the thin copper line that goes to the bypass valve. The next step is to check the air pump.

5. Loose the clamp between the air pump and the air cut-off valve. Disconnect the cut-off valve from the air pump. Start the engine. If your pump blows a good amount of air, you're good.


I've read someone's posting on "cleaning the air pump filter" and all of that. Although it's a good advise and I followed it, - you need to remove the whole vertical rectangular module along with the vacuum canister, don't try to disconnect 4 screws from the air pump plate that hold the air pump to a base plate - there is an air pump electrical connector snapped in to the base plate, you can break it if trying to unclip. Take off RL wheel, take the pate out, take out both thermocouple ECUs, the solenoids, and then 3 nuts that holding the air pump's base plate. Then the air pump and its' filter are all yours. BUT, as I said, taking out 4 small Phillips screws and taking out/cleaning the filter might help but less likely your air pump filter will be BADLY clogged so you get the air pump producing almost no air. So, this step is a "nice to have", if you want to. Wouldn't hurt. But it will not fix your issue. So.


5. If your air pump blows air, you good. If not: it's been operated by a relay "L" in the fuse panel in the passenger footrest AND with the fuse #31, 15AMP. That was my case. I had that fuse burned off. How did it happen? -Don't know. BUT, I think the trunk lid on 355 has grill holes all over + the connector of the air pump does not have and rubber sleeve protecting it from the rain water. Once you get caught in a hard rain (maybe it was my case) - and at that moment the ECU had the air pump operation = here you go, the fuse goes off.


The cut-off valve serves a function of shutting off the air channel to the cats if the one-way valves get bad letting the exhaust gases back to the air pump so it will not damage the pump. When your 1-way valve(s) goes bad - and they at some point WILL, the cut-off valve operated by ECU, shuts off the air channel to prevent the air pump from damaging, and you will get the P1448 code.



6. So, if your fuse is good, it might be a relay - marked on the picture with "L". I never had a relay died on me in the Ferrari. But, it's all possible.

7. Also, check the fuse #30 next to the fuse #31. It's for air injection ECU.

8. So, if you get your air pump sorted out, proceed. Connect the cut-off valve back to the air pump and disconnect it from the air channel that goes to the 1-way valves. Start the engine. If you have no air from the shut-off valve, check the valve. Take it off from the car, and get a 1/8 rubber vacuum hose and a plastic syringe from CVS or something. Pull some vacuum and blow into the cut-off valve. If the air goes through, you good. If not, here you go. Your P1448 error.


9. If the cut-off valve is good but when it was connected to the airpump, it was no air. Here is the trick. DON'T PANIC. The air pump ECU operates the way if the air pump is blocked by the cutoff valve, it shuts down the air pump. Don't take off the cutoff valve starting up the engine, the air pump will not be working. The ECU will keep it shout down for few hours. Leave everything like this. Do something else. Come back in 1-3 hrs. The air pump will blow again on the engine start.


10. If your cut-off valve is tested out in a good working order but not letting any air to come from the air pump, take off a vacuum hose from the middle of it, start the engine. If there is no vacuum in the hose, that means you have a solenoid valve dead = error P1448. There are 2 solenoid valves in 355 for this system: a left one and the right one. The left operates the bypass valve and the right one - the cut-off valve for air injection. If your right solenoid is dead, move the electrical connector AND the OUTBOUND vacuum hose to the other one and start the engine see if there is vacuum?


11. Way less likely both solenoid valves are dead. Because when first of them died, you will get a CHECK ENGINE with P1448 code. So more likely at least one of them is not dead.


12. If you have vacuum coming from RH solenoid (BLUE electrical connector), move the BLUE connector to the LH solenoid, start the engine. Your bypass valve should get opened. If not, disconnect the vacuum hose which goes from the top connector on the LH solenoid to the nipple from the copper line to the bypass valve. If this vacuum hose has cracks and holds no vacuum, here is your cause of the P1448 error code.


12. The other component left of this system are the solenoids electrical connectors. BLUE for Air for air injection, BLACK one is for bypass valve. The color codes speaks for themselves, pretty much. If everything else is in a good order but solenoid(s) not operating, the BLUE plug has 1 connector which terminates to the Ground and the other goes to Montroic ECU, for the 5.2 it's the: Row 3 64 Yellow Blue By-Pass Valve Flap.


13. A word on the thermo-couples:

- If you get P1448 error AND you SLOW DOWN light is FLASHING: replace the thermocouple on one of the LH or RH cats. Replace one and see if the light flashing no more (it will flash within about 1-2 minutes on the engine start)

- If you get P1448 error AND your SLOW DOWN is lit-up and stays: replace the middle thermocouple in front of the bypass valve.


That’s pretty much it.

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Thanks for the write-up, Alex. It will take me a few days to digest all of it, but I'm just wondering where you found this?

Just one problem, the thermocouple is downstream of the bypass valve, not upstream. I just checked on my car. Australians have the same setup as the USA (USA ECU, USA engine wiring harness). The pdf diagram also shows the thermocouple downstream of the valve.

The WSM also says this, but it doesn't make much sense to me:

"on the US version, the by-pass valve operation is controlled by the ECU, through a third thermocouple detecting the temperature downstream of the valve. The temperature increase, caused by the exhaust gases, informs the Motronic ECU about the performed valve opening (through the thermocouple and the relevant ECU)."

Both the 2.7 and 5.2 sections of the valve mention that the valve opening and closing to achieve the best counter pressure.

Cheers

 

Bad translation.

Thy this:

"on the US version, the by-pass valve operation is controlled by the ECU. Through a third thermocouple detecting the temperature downstream of the valve, the temperature increase, caused by the exhaust gases, informs the Motronic ECU about the performance of the valve opening (through the thermocouple and the relevant ECU)."

 

That is incorrect. You are misinterpreting the WSM and the OM,

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This is also incorrect.

Whether the SDL is on solid or flashing is dependent on the cat temperature
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Note that although fuse and relay location should be the same on the relay panel, the numbering differs from car to car. There are variations between 2.7 and 5.2 cars, and I've been told there are even differences between my '98 5.2 and very late model cars.

 

Hyperflow cats and tubi headers. I wish I could remember the codes I was getting with my hyperflow cats, I think it was cat inefficiency related. I used the big daddy extenders and have driven the car a few times since installing and I have no codes (none pending either).

 

The 3rd thermo-couple: correct; the thermo-couple is behind the bypass valve following the exhaust gases flow. If you stand behind your car looking forward, it will be in front if it between the bypass valve and the muffler.

The troubleshooting steps for the combination of P1448 code + flashing or solid SLOW DOWN light are also correct. Disconnect your thermo-couple one at a time and turn on the engine and you will see. What you misunderstanding from the Owner's and Workshop manuals' screenshot you posted is in the Workshop manual describes the functionality is based on the normal working thermocouples to advise you to slow down/pull over (blinking light) or immediately shut off the engine (solid light) and the troubleshooting steps are for when one of your thermocouples is dead.

The bypass functionality is based on if your bypass valve will remain closed when the 3rd thermocouple temperature increased, the bypass valve will not relieve hot exhaust gases from continue heating the cats so you will get the SLOW DOWN light flashing. You need to just think further of what is the bypass valve trying to mitigate/accomplish?

Fuse and location for the air injection pump is for 5.2. For 2.7 it might be a different location and/or fuse(s) #.
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- The cats efficiency error codes are a different topic. Not related to the air injection/bypass valve.

 

I'm only going to post this and I'm out of here. Agreed that you may get a flashing SDL is the by pass valve doesn't open correctly. This would be due to excess flow through the main cats and the resulting excess heating and excess pressure. This would be triggered by the main cat thermocouples (TCs), not the bypass TC. The TC after the bypass valve showing hot conditions does not trigger the bypass valve to open. It is an indication that the by pass valve is opened. 1448 applies to the bypass valve not fiunctioning correctly for any number of reasons, or a problem with the sensing system itself. The bypass TC can not get hot enough to cause a flashing SLD with the bypass closed before the main cat TCs would signal this because there is no flow through the bypass other than leakage which would come from the cooler upstream, higher pressure, pre cat side of the exhaust path. The bypass TC is an indication of functionality, not a driver of action.

Disconnecting TCs can cause an SDL because it will result is a max voltage signal to the ECU and the ECU will think a cat overheated.

 

No worries. To explain: by disconnecting the thermocouple you simulate the thermocouple that is dead as I said in the post in the above. When it sends no signals whatsoever at all. When either your thermocouples is dying and sending the wrong reading, it will be a different error code with: "Signal from Temperature Probe is out of range". It will not be a P1448 code.

Agree to the logic you described on what the 3rd thermocouple is for. Reading again the highlighted section of the p. #C41 of the Workshop manual, it's probably a poor translation from Italian to English when they were writing the manual.

 

I said I would step out but you have a mistake. When you disconnect a TC form the Vescoviai ECU it sends a full scale signal to the main ECU, 5V.

As for 1448,

 

Don't know of what you trying to proof in here for thermocouoples troubleshooting, if the thermocouple is dead or disconnected and the thermocouple ECU sends the signal to Motronic then what? Where am I wrong? Wrong that the thermocouple needs to be replaced? And if you prefer to follow your screenshot with steps forP1448, good luck to you; what can I say?

 

Would you please recheck your manual, Alex. The fuse next to the single relay on the same horizontal line is for the air pump in all my manuals (2.7 and 5.2). It's always the last one on the list. Directly above the fuse is the pump relay.


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Hey Ian,

Sure, here it is. As of MY99 355 F1:
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Thanks, Alex. I misunderstood your message. I think I got confused when you said "air injection ECU".

Did you mean the fuel injection (Motronic) ECU?

From car to car, the air injection fuse and relay's physical location remains the same. Just the identification letter/number changes in the handbook. When Ferrari rewired the 2.7 to create the 5.2, they made as few changes as possible to the wiring. The relay panel's internal wiring is identical.

 

Yes. Per the ECU connector pins layout the Motronic also operates the air pump. But a good point: if the Montronic' fuse #30 gets burned out, the engine wouldn't get started for the first place.

Can't speak of the fuses/relay location on the fuse panel for M2.7. I said for 2.7 it might be different. My owner's manual covers F1 M5.2 only.

 

Here's the 2.7 panel

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But fixed part of his problem!

Glad it got fixed I had the same issue with thermocouple ecu plugs being reversed when I got my car....seems mechanics just dont take the time to mark connectors properly. I had heard this issue several times here on Fchat. Enjoy