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Q: SES light on, car misfiring

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The car started misfiing, code P1288, P0300, P3002, P03304. Is this the result of a faulty CHT sensor?

My car has 138000 miles.
My car has an automatic transmission.

A: Hello. When multiple codes are recorded, su...

Hello. When multiple codes are recorded, such as in your case, generally the first code is the one to look at. However, the FSM for your vehicle will state which code to start with diagnostics. The reason for this is oftentimes that the "other" codes are merely reported as a consequence of the failure. In other words, some of the codes are spurious. For example, if P0300 has set first, you have a misfiring condition (there are multiple possible causes of that, not all ignition-related) or you could have a lean operating condition caused by a vacuum leak or stuck EGR valve causing a misfire. But that lean condition is also causing the engine to overheat. The overheating then triggers code P1288 for engine temperature out-of-range even though there is nothing wrong with the CHT sensor itself. This is just one scenario. A professional from YourMechanic can prioritize the codes using the FSM diagnostic tree, and then hone in on the failed component(s) or systems, each of which have to be tested separately to pinpoint the needed repairs.

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