What were he codes stored that brought on the Check Engine light, the code will be something like P0304 or P1457. Low oil pressure is not a problem experienced with Toyotas. Perhaps you have a bad oil pressure switch or low engine oil level but if in doubt it would be advisable to check the oil pressure using a mechanical oil pressure gauge. How many miles are on this engine, do you know the past service history of his car and what are the symptoms associated with the problems you are experiencing.