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Discussion Starter · #1 ·
Hi all, I know I have another thread going, but I wanted to put more of a focus on this. I have my car scheduled to go into the shop on Saturday because the check engine light came on. Well, while i was driving it this morning, the light was on and once I reached my destination, I shut off the car. I turned the car back on, an the light was still there. Well, in the Atlanta area, we are having bad storms (don't know if this is related), but I drove through some standing water and the light went away. First, is it possible for the computer to reset during driving or does the computer reset after x miles and re-runs the diagnostics? Nonetheless, the check engine light is not there anymore. I am hoping that the dealership is able to check the history of the codes to see what the hell is going on.
 

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It is entirely possible for a fault to "disappear". This is normal behaviour.
The fault that caused the CEL to be triggered might have been a random error that never happens again. For example the coolant temperature sensor could be seen as faulty by the diagnostics system for some reason, so a code is set and the error light is switched on. During normal operation the diagnostics system will detect that the sensor isn't actually faulty and will set the error code from 'active' to 'inactive' and turn of the error light. The fault will still be present and can be checked with the necessary tool. Manufacturers have different thresholds as to when a DTC is ignored, can be X amount of times the car was started since DTC was set, X amount of miles driven, X amount of ignition cycles, condition Y or Z or K was met and so on.
This doesn't happen for all DTCs, most notably the SRS-system (airbags) will always require manual deleting of DTC before the light is off again.
 

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Discussion Starter · #3 ·
It is entirely possible for a fault to "disappear". This is normal behaviour.
The fault that caused the CEL to be triggered might have been a random error that never happens again. For example the coolant temperature sensor could be seen as faulty by the diagnostics system for some reason, so a code is set and the error light is switched on. During normal operation the diagnostics system will detect that the sensor isn't actually faulty and will set the error code from 'active' to 'inactive' and turn of the error light. The fault will still be present and can be checked with the necessary tool. Manufacturers have different thresholds as to when a DTC is ignored, can be X amount of times the car was started since DTC was set, X amount of miles driven, X amount of ignition cycles, condition Y or Z or K was met and so on.
This doesn't happen for all DTCs, most notably the SRS-system (airbags) will always require manual deleting of DTC before the light is off again.
Thank you so much for the info. Will the dealership be able to go back to the codes to see what triggered the light after it is gone?
 

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They should be able to see the code(s) that triggered the light. Like I wrote: The code will be set to 'inactive' or 'intermittent' but will remain present until it is cleared.
Just be aware that some DTC(s) will be cleared by the car itself if certain conditions are met. I don't know what parameters Volvo has chosen for the XC90 II but in the past some codes were cleared after 50 ignition cycles. This would mean that there would be no logs of the codes or any freeze frame data connected to the DTC(s).

If you can it would be great if you posted the diagnostics results.
 

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Discussion Starter · #5 ·
They should be able to see the code(s) that triggered the light. Like I wrote: The code will be set to 'inactive' or 'intermittent' but will remain present until it is cleared.
Just be aware that some DTC(s) will be cleared by the car itself if certain conditions are met. I don't know what parameters Volvo has chosen for the XC90 II but in the past some codes were cleared after 50 ignition cycles. This would mean that there would be no logs of the codes or any freeze frame data connected to the DTC(s).

If you can it would be great if you posted the diagnostics results.
Thanks for the info. When you're referring to the diagnostic results, are you referring to manually running one through the car status app or from the dealership?
 

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Meant the dealership. The car status app is not meant to diagnose faults of this nature.
Just ask the mechanic or whoever is available for a print out. I assume your problem will be under warranty, if it even is a problem, but one can never be to careful. Documentation is important.
 

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Hi all, I know I have another thread going, but I wanted to put more of a focus on this. I have my car scheduled to go into the shop on Saturday because the check engine light came on. Well, while i was driving it this morning, the light was on and once I reached my destination, I shut off the car. I turned the car back on, an the light was still there. Well, in the Atlanta area, we are having bad storms (don't know if this is related), but I drove through some standing water and the light went away. First, is it possible for the computer to reset during driving or does the computer reset after x miles and re-runs the diagnostics? Nonetheless, the check engine light is not there anymore. I am hoping that the dealership is able to check the history of the codes to see what the hell is going on.
The best advice I see here is to document everything with proof of delivery (certified mail etc. ) communications. Telling someone about something serious like this without proof is the most likely road to future problems.
 
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