Question:

what do the codes say???

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How do I check the codes?  I assume I will have to take it to a shop or find a way to read the codes?  Correct? And once I get results from testing, what will the codes likely tell me?

Response:

The codes will give a direction to go in the diagnostic process – the first need to be deciding if the code(s) are a symptom (much like lean fuel codes could be an effect of a plugged fuel filter) or a cause (a TPS code is *usually* a cause – though wiring and/or the PCM can also be the problem). I understand that AutoZone will scan for codes for free though I am unfamiliar with whether they use the correct procedure. For those that would like to know…. the first step in code reading is to check for Continuous Memory DTCs (problems the PCM has detected but may not be present at the time of the test) – note any codes and clear them. Next are the KOEO On Demand DTCs – these are faults the PCM can see at the time of the test – ones that are there NOW. EEC IV vehicles would perform a timing check at this juncture but OBD II vehicles don’t have a spout connector. Next would be the KOER self test – These would be a ‘hard’ code, actually an engine running On Demand DTC. KOER DTCs might include some or all of the previously recorded CMDTCs (since they required the motor to be running to test those inputs and outputs). KOEO codes get fixed first, then the QuickTest is run again. CMDTCs are the last to receive attention (unless they turn out to be KOER On Demand codes). If all you have to work with are CMDTCs, be prepared – these are usually intermittent and can be a real bear to track down. While you’re at AutoZone, don’t forget to pick up a manual with some decent wiring diagrams and code descriptions…. Good luck, — Jim Warman

– Hide quoted text — Show quoted text -> How do I check the codes?  I assume I will have to take it to a shop or > find a way to read the codes?  Correct? > And once I get results from testing, what will the codes likely tell me?

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While driving my 96′ XLT, 4.0 Liter over the weekend in winter conditions, snowy, slick roads.  I hit a pot hole, a decent jolt but nothing out of normal, the check engine came on a second after hitting the pot hole.  The owners manual says it could be the fuel cap being loose, I checked it, tightened it and the light is still on, other possible causes list as ‘take to your service tech’ as the remedy. Does anyone have any ideas what this could be.  All the gauges seem to be working fine, all readings are normal, vehicle is running fine as usual, just the light is on.  My initial thoughts are something might have been stuck because of the cold weather and the jolt knocked something loose making the light come on. Any ideas or similar experiences? Thanks

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