Technical P0300, P0302

[alesinwales]

Hi all,
been dealing with these codes for a while. Already took the car 4 times to the garage, but this codes are still showing interminently.
Plug sparks, coil packs and leads have been already replaced several times.
The issue comes randomly when driving out of town. Sometimes after 10 miles, sometimes after 5 or 40.
Car goes on limp mode. I need to turn then engine off, wait 1 minute and then the car runs smoothly.
Big issues is that when the car goes on limp mode the breaks stops working properly (like when the engine is off!). This is very scary and dangerous. This started to happen recently, last year the car would say on limp mode and run for miles at 30mph...
Do you guys have any tips on reasons for this issue? More importantly, how can I avoid the brakes for malfuntioning? or any ways to avoid the brakes to malfunction?

Thank you

 

[FiatMatt94]

I had something similar last year where it would go into some sort of limp mode with no throttle response with esc & hill hold not available, switched off then back on & all would be fine, after I replaced the earth strap that goes from the gearbox to body & it probably wouldn't hurt to replace the negative battery strap at the same time, problem was solved, the gearbox to body one is very exposed where it is located & it is a braided strap from factory, to which my one was very badly corroded, it's a similar issue to which I had so hopefully this helps

 

[alesinwales]

I had something similar last year where it would go into some sort of limp mode with no throttle response with esc & hill hold not available, switched off then back on & all would be fine, after I replaced the earth strap that goes from the gearbox to body & it probably wouldn't hurt to replace the negative battery strap at the same time, problem was solved, the gearbox to body one is very exposed where it is located & it is a braided strap from factory, to which my one was very badly corroded, it's a similar issue to which I had so hopefully this helps

Thank you. I will mention this to the garage on Monday. How much did it cost you to do all that?

 

[FiatMatt94]

Thank you. I will mention this to the garage on Monday. How much did it cost you to do all that?

It cost me less than £10 as I do some off my matainence & my dad does the rest, with the battery removed you should be able to see the braided strap, although I just replaced it with a normal earth strap

 

[Terry899]

It helps when you get to know your car and start doing little bits yourself, use YouTube to help with any advice you get here if you can't understand what you are advised to do. Remember there are many answers to whatever problem you have, the difficulty is picking the most likely one. Garages are getting less capable as the younger lads plug in the computer first and can be stumped when it doesn't have the answer.

 

[Herts Hillhopper]

Hi all,
been dealing with these codes for a while. Already took the car 4 times to the garage, but this codes are still showing interminently.
Plug sparks, coil packs and leads have been already replaced several times.
The issue comes randomly when driving out of town. Sometimes after 10 miles, sometimes after 5 or 40.
Car goes on limp mode. I need to turn then engine off, wait 1 minute and then the car runs smoothly.
Big issues is that when the car goes on limp mode the breaks stops working properly (like when the engine is off!). This is very scary and dangerous. This started to happen recently, last year the car would say on limp mode and run for miles at 30mph...
Do you guys have any tips on reasons for this issue? More importantly, how can I avoid the brakes for malfuntioning? or any ways to avoid the brakes to malfunction?

Thank you

The engine provides a vacuum to the brake servo unit (‘power assistance’ for the brakes). If the engine stops, or the vacuum pump is faulty, the brake pedal will need a much harder push to function.

those codes show a generic ‘misfire detected’ and that it’s occurring on cylinder 2. Although that could be caused by spark plus or coils, it can also be caused by air leaks, fuel supply issues and vacuum issues… which might relate back to the brakes.

 

[Herts Hillhopper]

Thank you. I will mention this to the garage on Monday. How much did it cost you to do all that?

This is the classic sign of poor electrical power - either a dying battery, or, as here, a poor connection somewhere. And then, low voltage or poor connections leads to ‘wrong’ error codes being shown

 

[Panda IIs]

This is the classic sign of poor electrical power - either a dying battery, or, as here, a poor connection somewhere. And then, low voltage or poor connections leads to ‘wrong’ error codes being shown

Yes, my experience is low volts cause all sorts of spurious codes and issues as sensors fail to power up properly or are not receiving the correct signals (Fiat and other ECU "loaded" marques). I had another example today (2006 Volvo) where airbag lights latched on, electric seats were no longer electric (adjustment) and widows failing to retract and return on door opening (it's a C70). This was all fixed by having the battery fully charged and a visit via the OBDII of VIDA (Volvo MES equivalent). A quick reset of all the modules and the car's as good as new(ish). It is new to my ownership and the previous owner tried to jump start a flat battery causing the carnage. The battery had a parasitic drain from the Volvo "on call" telephone link (may sound familiar to anyone who has suffered a Blue and Me failure in their Fiat?). Solution, disconnect the hardware... Also, a familiar solution!

I can imagine a dodgy earth strap will cause similar symptoms.

My 2003 Merc W211 estate really stresses out if the battery is allowed to run low (after a period of SORN for example) as it has the "brake by wire" SBC brake system that is pressurised by an electric motor. Fortunately it responds well to a quick charge!

 

[alesinwales]

Thank you all,
Took the car to the garage: they admitted they have no clue what it could be. They suspect it is the ECU.
They recommend I take the car to a FIAT dealer. I contacted one, and they told me that it might take them days to find the issue because it is intermittent.
I am driving slowly now, and the car faulted again. This time, as I was going slower, I realized that the engine shuts off in less than one minute. Just enough time to stop the car and run an OBD-II scan (which gave me the same misfire codes: P0300, P0302).
Do you guys have any suggestions?

 

[Terry899]

Thank you all,
Took the car to the garage: they admitted they have no clue what it could be. They suspect it is the ECU.
They recommend I take the car to a FIAT dealer. I contacted one, and they told me that it might take them days to find the issue because it is intermittent.
I am driving slowly now, and the car faulted again. This time, as I was going slower, I realized that the engine shuts off in less than one minute. Just enough time to stop the car and run an OBD-II scan (which gave me the same misfire codes: P0300, P0302).
Do you guys have any suggestions?

Great garage that it's a simple car, I've no doubt someone here has had the same issue as you. I'll throw in an odd ball suggestion, fuel filter is newish and after running when you open the fuel filler, you can hear air rushing into the tank? If so it's not that.... I once had a kink in the fuel line where the body and engine meet and my car would stutter and sometimes cut out

 

[Herts Hillhopper]

@Terry899 Did you see my earlier reply - repeated here:
“those codes show a generic ‘misfire detected’ and that it’s occurring on cylinder 2. Although that could be caused by spark plus or coils, it can also be caused by air leaks, fuel supply issues and vacuum issues… which might relate back to the brakes”
‘Fuel supply issues’ can include poor fuel tank venting, and vacuum issues could be the vacuum pump or the pipework running from it.

 

[Panda IIs]

Thank you all,
Took the car to the garage: they admitted they have no clue what it could be. They suspect it is the ECU.
They recommend I take the car to a FIAT dealer. I contacted one, and they told me that it might take them days to find the issue because it is intermittent.
I am driving slowly now, and the car faulted again. This time, as I was going slower, I realized that the engine shuts off in less than one minute. Just enough time to stop the car and run an OBD-II scan (which gave me the same misfire codes: P0300, P0302).
Do you guys have any suggestions?

So, did you check out electrical issues? Battery voltage low, just ageing battery? I would be somewhat surprised if it is an intermittent ECU issue, I'd expect it to work, or not.

My money would be on an electrical (volts) issue. Is your code reader just a generic one? This may be sending you down a rabbit hole. Perhaps find a local independent FIAT(Alfa) tech or go the main dealer route for a thorough OBDII looksee?

Just some thoughts - not based on the same experience as you are having.

 

[The Panda Nut]

This was the first sign of the evapouration solenoid playing up on ours.

 

[Terry899]

@Terry899 Did you see my earlier reply - repeated here:
“those codes show a generic ‘misfire detected’ and that it’s occurring on cylinder 2. Although that could be caused by spark plus or coils, it can also be caused by air leaks, fuel supply issues and vacuum issues… which might relate back to the brakes”
‘Fuel supply issues’ can include poor fuel tank venting, and vacuum issues could be the vacuum pump or the pipework running from it.

Didn't see your reply, tough problem to pin down over the Internet, you'd have to have the car to tinker with and observe the results. Ideally another similar car to swop bits over would be the cheapest and help deciding if it's a wiring issue