rbaron

I was driving around town one day last week in my new to me but well PPI'd 2017 base Macan. It was a very hot day (100F+).

I got a warning to the effect of check engine but you can still drive (see image below); reseating the gas cap did nothing (it was tight to begin with) but that was the only day I got the message.

How long, if at all, is a fault code such as this retained in the car's computer?

I tried to search for an answer but I guess I'm too wordy b/c I couldn't find it.

Thanks,

--Bob

PSEE

I understood faults were retained until (electronically) cleared...

wwahl

Yes, I had a long session where the dealer had to clear dozens of code problems. They turned out all to be passive, but they were screwing up my driveability. Guess who had to pay for this? Me.

DHL

That looks like a "Check Engine" light caused by a fault in the OBD system. You need a scanner to determine what fault has occured. Some OBDII fault codes will automatically cause the Check Engine light to clear if the fault is not present continuously. But not all. And I believe that the "code" is stored in the car until cleared with a scanner. After clearing, certain software watchdogs are set to monitor condition of the car and you have to drive a certain distance under specific load conditions to reset the "monitors". Once they are reset, the fault is gone for good. But if it re-occurs, the check engine light will come on again and you start all over again. Any good shop or dealer can scan your car to determine what fault code was thrown. Not sure about Porsche, but most cars can be scanned with inexpensive OBDII scanners you can obtain at any auto parts store. If the fault code is specific to Porsche (not one of the standardized codes) then the cheaper OBDII scanners will not read it. Some of these scanners will reset the code as well, but even doing so will trip the monitors to run so a standby condition is set until they clear. Here in CA, you cannot pass smog if only 1 monitor has not reset and there are any uncleared codes, which is a major PITA.

gellenole

Fault codes usually are retained until a few things happen:
1 - sensor notices that issue is fixed (eg. if something is unplugged and it gets plugged back in) - then car is turned off then restarted
2 - manual reset needs to happen (eg. find an ODB-2 / ODB-II clearer - amazon will have stuff like that from 50-200 (depending on how fancy you want it and if it has the capability or functionality))
3 - unhook battery and let it sit there for a few mins (10 or so I would believe would be more than enough YMMV)

you can also go to your local autozone or local car parts shop, they usually have a code clearer that you can quickly borrow for free. plug it in, scan it with the key in the acc or on position (scanner will tell you) and then read and clear it yourself.

DHL

Not quite.
Pulling the battery will not reset the monitors even if a code is cleared. OBDII faults are part of the federally mandated emissions control system and the cars are smart enough to retain memory of an emissions fault even if power is removed.

If the fault never returns (the car is repaired or the fault was intermittent) the original fault code is retained in memory until reset by a scanner designed for the purpose. The check engine light may go out and you can drive the car normally, but the fault code is stored indefinitly until reset. If you are in a state like California, the smog stations connect a computer to your OBDII port and if there are any uncleared codes or incomplete monitors, they will not pass the car for smog and you cannot renew your registration. I don't know how many other states are similar (NJ, NY?), but most are not as strict.

rainer

There's 4 types indeed:

1. Some codes disappear after re-start.

2. Some won't.

3. Some codes have a counter which clears them automatically after several re-starts (engine off/on), cannot remember it it was 30 or 50 starts.
Special case:
Some of the emission related codes need a certain amount of miles (not re-starts) before they get deleted. If you're too early for emission check, you may fail it as it is a measure to prevent clearing those just before you go through an emission test.

4. Plus. the last 20 warnings showing as text messages in the right dash instrument are stored and can be looked up with Piwis.

gellenole

interesting thing enough - maybe unique to my car. usually power off code resets.
I do disconnect battery for a while. tried it a couple of times - unless it's a fault with legal things (eg exhaust related or fuel related) all items cleared after battery is pulled.
Only major thing I tested:
- the value open/close actuator. and after plugging the actuator back in then battery unplug - scanner said code never existed (also verified that during replug the fault code stayed on until battery pull).
- unplugged a couple of vacuum hoses until fault came on and did the same -- plugged it all back in, validated that code stayed on, pulled battery -> boom gone.


dunno -- anyway it's just based off of my experience.

DHL

Did you check the status of the monitors after pulling the battery? Because a scanner can also reset the code (and a subsequent scan will show no codes), but that activates one or more monitors to run that will throw another code if the problem is not repaired.

gellenole

yah, scanner code cleared before connection -> then reconnected to see if it picks up code -> no codes.

c1pher

Hopefully not as long as my wife remembers.

DHL

Yes, maybe no codes but a number of monitors are now set to run. If they make it through their respective driving cycles without the fault code re-appearing, they code will remain deleted. If the underlying fault is still present, the CEL or codes will re-appear.
If you need to pass emissions inspections (at least here in CA) while ANY monitors are still running, you will fail inspection. In other states they may allow certain monitors to be running and still pass inspection, but which ones and how many are up to local laws.

DHL

I believe that any OBDII emissions code will be retained in memory unless reset by a scanner (or pulling the battery for an extended period). The CEL (check engine light) may or may not re-appear after a restart but the underlying code is still there. CEL may also extinguish on their own if the fault does not re-occur and operation of the vehicle is not compomised. But the code is still in memory. This is to allow any shop to scan for errors/codes even if the problem has not re-ocurred or the cause is transient. Once a code is reset, a plurality of monitors that measure the conditions of the underlying systems (catalyst, cooling system, evaporative fuel system, etc) are activated to monitor the car's performance over a specific driving cycle, individual to each monitor. If you try to have your car pass emmissions inspection while a monitor is still active and has not completed it's test cycle, the measurement agency may not allow your car to pass. BTW, it is not recommended to clear codes by pulling the battery because when power is restored, the largest number of monitors are activated which can take the longest time to run. Clearing a specific code with a scanner activates only the relavent monitors related to that code.