Common engine codes for a Dodge Ram are HO2S (heated oxygen sensor), MAF (mass airflow), MAP (manifold absolute pressure), IAT (intake air temperature), ECT (engine coolant temperature) and TP (throttle position). Detailed owner's manuals can be downloaded from Dodge Ram's official website for free for vehicles from 2004 and later.
Many automotive stores and service centers, like AutoZone, Pep Boys and Jiffy Lube, provide free diagnostic testing for check engine lights as of 2015. Usually the store can provide a printout of the engine codes, also known as Diagnostic Trouble Codes (DTCs), that need attention. This printout can be used to attempt simple repairs at home or taken to a mechanic who may use it as a reference.
The DTCs can also be checked by cycling the ignition switch on, off, on, off and on within five seconds. After the cycle is completed, the odometer shows the P-code that represents the affected DTC. Codes P0030 to P0058 and P0130 to P0141 point to an issue with the HO2S. For example, an odometer display of P0030 indicates a problem with the HO2S Heater Control Circuit. If the odometer displays P1684 and/or DONE, then the diagnostic system has not registered any problems with the vehicle.