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I was travelling in my 2018 WRX CVT when I had a transmission stall while driving on the highway. The day it happened I had spent the night, and temperature was very low ~30F. (as compared to the 70-60F temps when driving up). I started the car with no issues, and let it idle until RPM's dropped and the car was at operating temperature. I started driving with no issues, until about an hour into the drive on the highway when the RPM's rose (~500-700 RPM's) suddenly, coupled with pressing the accelerator that did nothing. I then slowed down to pull over, when I reached about 30 mph the car shuttered and stalled to a stop. I tried starting again, but the car would not hold an idle and promptly died. I repeated this 2 more times to the same effect. The last time I started, I was pumping the gas which seemed fixed the issue, the car idled and drove fine.
I brought the car in for service and was told that a P1603 Error code was stored in the TCM which was then cleared. I asked them what the code meant but did not receive a direct answer. I did some research and from what limited info I could find the most likely issues is related to the IG1, IG2, ACC1, ACC2, and EGI Relays flash freezing. But other sources stated issues with the car over-retarding the timing triggering a check engine light, or faulty MAF or MAP Sensors. However, this data is not directly related to the WRX, but Subaru's with the CVT transmission as a whole. I don't know if this could be related to the cold temperatures and the car overcompensating for knock by retarding the timing, or if its an issue related to the transmission.
I am just curious if anyone had a similar issue, and what the code means for the transmission and vehicle, and if anything further should be checked?
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