DTC Code Meaning

i suppose the toyota tech manual, but some can be googled.

 

Google " Complete list OBD II codes" and choose the Green hybrid post for a big list of them

 

Hmm, well, a little bit about DTC definitions ....

The basic categories (starting letter and first digit or two) are standardized by organizations like SAE, and within each category there are ranges set aside for codes with standard meanings (the same across makes and models) and other ranges set aside for manufacturers to define their own. A code in a manufacturer-defined range can mean quite different things from one make or model to another. You can Google up lots of giant code lists on the interwebz, but how many of those pages make it clear which of those codes even apply to your car? (How many of those pages would you guess are even put up by people who understand the difference?) How much of your time are you willing to blow finding out, or going down a rabbit hole because some DTC list said your problem was with a part your car doesn't even have? (Seen it happen on PriusChat.)

But the bigger point is ... finding on some list what some DTC means is almost ... not quite, but almost ... useless. There are lists on the net and there are lists built into some scan tools, and it's the same deal: you'll get this line that says "oxygen sensor" or something, like a fortune cookie.

The thing is, the computer in the car is stuck in a box. It can't get out, and everything it knows about the car has to come in on the wires it's connected to. If the computer throws a code that's listed as "oxygen sensor", for example, that means it is getting an electrical signal that isn't supposed to be right for an oxygen sensor. All it can see is the end of that wire. Whether the problem is really with the oxygen sensor, or the wiring, or the power supply to the wiring, or the catalytic converter, or the fuel injectors, or anything else that could be affecting the conditions the sensor is measuring, the computer can't tell you, because it's stuck in a box. Those questions have to be answered by someone who can move around, test things, and draw conclusions, someone like, you.

So am I saying the DTC isn't helpful? Far from it, the codes are hugely useful, because they start you off knowing what questions you will have to follow through and answer to find out what's wrong with your car. But you have to do the legwork on those questions, because you have legs, and arms, and opposable thumbs, and the computer doesn't.

Your repair manual will help you greatly with that, because when you look up your code in your manual you're going to find a page number taking you to anywhere between one or two, or ten or twenty pages of steps you can follow to find out why you are getting that code. It will tell you what measurements the computer actually is making to decide to throw that code or not, and where those values come from, and what could be causing out of range ones, and what concrete tests you can do to find out. Those pages are pure gold if you want to solve your problem.

A list of DTC "meanings"? Well, who doesn't like fortune cookies?

-Chap