It was a brief decade ago that the modern “check engine” light emerged. Though it looked the same, it fronted the second generation of “on-board diagnostics,” a.k.a. OBD II. With OBD II came a standardized format for stored codes (formally known as “diagnostic trouble codes” or DTCs in tech jargon)—five digit hexidecimal codes, to be exact. P0301 is now known as “Misfire Detected Cylinder #1.” P0455 points to the gas cap. There are hundreds more.
Hybrid owners are advanced in their automotive fluency, both because their cars are high tech and owners themselves are more interested. But the cars have done their part to up the ante. With the popularity of the Prius comes a newfound warning indicator more ominous than “check engine:” a red triangle fondly known as “the red triangle of death.” Not only that, owners must negotiate a secondary level of diagnostic trouble codes, “information codes” also known as “INF codes” or “sub-codes.” Without this data, the DTC is too vague to properly (or efficiently) diagnose.
Witness the dreaded P3009, for instance. Generally it describes a voltage leak (short) somewhere in the Toyota hybrid system. People often worry about the high voltage wiring being chaffed somehow, causing this code. It’s better known on the Gen 1 Prius, whose undersized drive motor is prone to fatigue (and eventual failure). The failure aspect often comes in the form of the P3009.
High voltage spans the length of a hybrid, from battery to motor-generator. So how do we know where to find (and therefore fix) the problem? Help comes in the form of information codes. I’ve copied the first page of the 18 page instructions pertaining to P3009 on the 04 Prius; note that there are five different sub-codes: 526, 611, 612, 613, and 614. Each points to a different aspect of the high voltage system. The HV ECU quarantines the problem depending on the operating conditions when the leak is detected.
The details and their importance are largely private to the technican in getting the job done. But awareness of Information Codes is essential to the vehicle owner when it comes to warranty disputes or elusive repairs. When multiple people get involved, a DTC alone is not enough to understand the situation. In record keeping it’s now essential to list not only the main codes but any secondary information of importance as well. Who’s to say if and when that information may be needed, and after clearing the code, it’s a guess to say what it might have been.