Diagnostic Tech: 2011 Toyota RAV4

 The complaint here was that several warning lights were on. The "check engine", "traction control" and "4x4" were on steady as I drove it in. 

The customer said the lights all came on at the same time. Any engine performance fault seen by the system would also turn on the other lights so I expected to see an engine performance problem, perhaps a misfire. Warning lights turn on when a computer has seen a problem that warrants attention. A trouble code related to the fault should be stored and you will need that code if you want to know what the computer is trying to have you check. I did find an engine performance related code, actually two. 

 The P0171 means the fuel mixture was too lean, not enough fuel or too much air. P0101 means the measured airflow at the mass air flow sensor doesn't match what the computer expects to see based on other inputs. C1201 is an empathy code. It means the engine control fault has placed these other systems into fail-safe. They will revert from fail-safe once the performance problem is repaired. The problem appeared soon after a service/maintenance job so it seemed a good idea to look around for something related to that before getting more involved, and there it was. A small breather tube had been left disconnected from the air intake hose. 

That open hole allowed air to enter the engine downstream of the air flow sensor. The extra air was setting the lean code and the air flow code. Now you can't just do a fix and be done. Eventually the computer would figure out the problem was fixed and turn the warnings off but that could take quite some time. It would have to see the monitors run and see that the same problem did not occur for several cycles. (On that note, never disconnect your battery to clear codes. Never.) You have to tell the computer the problem is fixed. Clear the stored codes with the scan tool. The computer will still run tests and will still watch for faults but the lights will be off until there is a problem. Many cars now store the codes in a memory called "permanent" codes that can't be cleared until the computer verifies the fix and clears them on its own even though the lights are now out. 

Before clearing codes though, I want to show you that more than codes are stored in the system. The conditions at the time of the failure are stored as a frame of sensor data. Once the codes are cleared the data is gone as well so lets look now before we clear. 

Given the conditions if I didn't know the air flow was incorrect I might suspect a fuel delivery problem. The point though is that there are several ways the computer can store and aid in your diagnostic journey. Use them. 

I cleared the system and all is good. 

Thanks for reading!

Kenny@ggauto.repair