I already have an inspection code why do you want to charge me 70.00 the code is P0304
My car's transmission is unknown to me.
P0304 is a "trouble code". The diagnostic fee that you are probably referring to relates to a check engine light diagnostic. The cost component in the check engine light diagnostic involved in merely downloading the "code" is trivial and, indeed, you are pointing out that you have already obtained the code and thus you should not be charged for it. You are correct. But, the problem is within that simple 5-digit code [P0304] there are many, many possible causes of the fault (misfiring in this instance) that could have caused the code to set. The mechanic must figure out, from what is a long list, which of those causes is the operative one, that is the one that must be repaired. To figure out, via a diagnostic, which of those many causes represents what must actually be repaired is not trivial in terms of time, required instruments and so forth. And, that is where the $70 cost arises. Indeed, in some cases, where the cause of the misfiring is due to multiple, coincident failures, or causes that are literally at the very end of the diagnostic decision tree, the customer has obtained an absolute bargain for the $70. To summarize, you are not being charged for merely a 5-digit code but rather for a complex endeavor which, at the end, will pinpoint the fault that has occurred in your vehicle.
With regard to your vehicle, among the causes of cylinder misfiring are faulty spark plugs, low compression, damage or excessive wear of spark plug wires and/or coils, faulty fuel injectors, clogged EGR valves or tubes, burned valves, improper ignition timing, vacuum leaks, leaking head gasket, faulty camshaft sensor, faulty crankshaft sensor, faulty mass air flow sensor, faulty oxygen sensor, faulty throttle position sensor, faulty catalytic converter, and others. If you want the specific cause pinpointed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a misfiring diagnostic and the responding certified mechanic will get this promptly diagnosed and resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic because we want you to make the most of your repair dollars and help you to get the best possible results.