What do these codes mean together?
Paste the list of codes your scanner gave you. We explain each one and — more importantly — what they mean together: several codes often come from one cause.
Paste anything: a list with commas, lines copied from another app, words in between. We will find the codes ourselves.
Why read them together
A reference answers about one code at a time. A car almost never gives one: it gives a list, and the list has its own meaning. Two codes about the same sensor are one fault, not two. Both sides of the engine running lean point to a cause before the intake splits. Misfires alongside a lean mixture are usually the consequence, not a separate problem.
Try it on a real list
Three lists that come up most often:
How to read a list of codes
Four rules that turn a list into one question. They are the same rules the reader above uses.
Same sensor, two codes — one fault
«Circuit» and «signal out of range» for one sensor are two views of the same trouble. Fix it once and both go.
Both banks at once — the cause is before the split
P0171 with P0174 cannot be two identical leaks. Look where the intake is still common: the meter, fuel pressure, a big leak.
Misfire next to a lean mixture — usually a consequence
The mixture came first, the misfire followed. Chasing the misfire while the mixture is wrong replaces good plugs.
Catalyst code with a mixture code — the catalyst is the victim
Replacing it without curing the mixture buys a second one for the same lifespan.
What the list does not say
The order of codes is not the order of events: the unit lists them as they lie in memory, not as they happened. And the number of codes is not a measure of how bad things are — one flashing-light misfire is worse than five codes about the fuel cap.
What does say something is the state of each code and its freeze frame: active or stored, and under what conditions it appeared. Those two answers narrow the search faster than any list.
Where the codes come from
Any OBD-II adapter reads them: the app connects, asks the car and shows the list. If you do not have an adapter yet, the guide on choosing one is here.