Naive questions about Diagnostic Trouble Codes (DTC)

[pmatejcek]

So I got a DTC reader; now I'm REALLY dangerous...

I'm confused about several things.

I have a 2006 V6 RAV4. I have been getting CEL / VSC / 4WD lights. They come on, they go back off sometime, they come back on....

I hooked up my new code reader; at the time, the warning lights were all off. It told me that I had stored codes P0606 (ECM/PCM Processor) and P0138 (O2 Sensor Circuit High Voltage). It also told me that I had pending code P0606.

First naive question: What the heck is a 'pending code'? My SWAG is that is saw something it didn't like, reset it, and is taking a 'wait and see' approach. What does it mean really?

Then I cleared the codes; the CEL / VSC / 4WD lights all came on! Grrrr. Could that have been because it was in that waiting period, and I killed that?

After clearing the codes, I now have a P606 stored, and a P0606 and P0138 pending -- and the lights persist.

Does anybody know what this means? A naive guess is that I've got an O2 sensor failing. (I was surprised to hear that I have four of them...) What about the ECM / PCM business? Does that mean that the main board is complaining / failing? ...or does that always happen when an error like the O2 sensor comes up?

I've read in another forum that the 606 really does seem to mean that the ECM is failing / failed. That should be an 'extended warranty' item. Hopefully, the O2 sensor is, also.

It looks as though I'll be taking it to Toyota. But I'm hoping that I'll be able to put this code reader to SOME use, on both the RAV4 and the Corolla. If nothing else, I'd like to be able to say, "That's serious," or "That can wait." Any advice on how to get smart about sorting out the real meanings of the codes?

Thanks for your patience and any related thoughts you can share!

Paul in East Troy WI

[co_mtn_grl]

Here is a link to a previous thread regarding those warning lights. It is a common occurance, happened to my 07 Sport earlier this week in fact:

Check Engine Light/VSC & 4WD lights explained

[pmatejcek]

Thanks, co_mtn_grl. I read it previously. I'm trying to learn what more detailed information I can glean from the actual codes, and whether there's any particular significance to these two codes together, and the meaning of 'stored' versus 'pending' codes.

Regards,

Paul in WI

[nouse4aname]

Actron®
What are Pending Codes?

OBD II Pending Codes are also referred to as “continuous monitor” and “maturing codes”. An intermittent fault will cause the computer to store a pending code in memory. If the fault does not recur within 40 warm-up cycles, the code will be cleared from memory. If the fault recurs a specific number of times, the code will then mature into a diagnostic trouble code (DTC) and the MIL or “check engine” light will turn on.

[niko4]

pmatejeck,

We are having the exact same issue with our 2007 Rav4. Same lights coming on and off and the same 2 error codes. Any information on what you did to resolve this problem would be greatly appreciated. Thanks!!!!