QuestionWhat are the usual causes of code P0300? Dealer says he can't do any thing unless CEL is on when he gets car. He can't duplicate the problem. It only happens at start up and light stays on for varying amounts of time. 2006 V6 Sonata LX
AnswerThere are two types of causes of P0300:
1. Anything that could cause the vehicle to misfire. This could be mechanical, fuel-related, ignition related, or fuel management related.
2. An engine control module (ECM) perceiving a misfire that isn't actually present.
I'm confused as to why the dealer needs the lamp to be on to perform some basic diagnosis. As long as the vehicle is taken for service in a timely manner, the code should still be present even after the lamp goes out, and information regarding the circumstances under which the code set (freeze frame data) should be stored in the ECM.
Unless it's already been done, I'd say the ECM needs to be reprogrammed. Hyundai released a technical service bulletin (TSB) in January to correct:
-- Diagnostic trouble code P161B,
-- Rough idle on cold start, and
-- Diagnotic trouble code P0111.
Presuming your engine is actually misfiring/running rough, this reprogram should apply. It's detailed in TSB 10-FL-002, which you can view by registering for a free account at hmaservice.com.
It sounds to me that, for whatever reason, the dealer does not wish to reprogram the ECM and/or spend the time necessary to diagnose the issue. If you haven't done so already, express your dissatisfaction to the service manager to see if that leads to a reasonable resolution. If not, contact Hyundai consumer assistance at 800-633-5151. You might also consider taking the vehicle to a different dealer.
