Engine Controls - Clearing DTC's

SOURCE: Honda Service News

TITLE: Clearing DTC's in Generic OBD II Mode or With a Generic Scan Tool

APPLIES TO: All OBD II

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Honda vehicles, like all vehicles certified for sale in the U.S. since 1996, must comply with a common data communication protocol known as On-Board Diagnostics II (OBD II). Vehicle manufacturers can have their own communication system as long as they comply with the OBD II requirements.






American Honda has supplied two different scan tools to Honda dealerships. The first to come out was the PGM Tester. It services all '92-03 Honda vehicles but it's no longer supported by American Honda. The latest evolution is the Honda Diagnostic System (HDS). It's the PGM Tester's replacement and it services all current Honda models as well as the older ones. The HDS, like the earlier PGM Tester, features a Generic OBD II mode. In this mode, the HDS works the same as any aftermarket scan tool. A Generic OBD II scan tool must be able to display DTCs and to clear them. If you try to clear DTCs on a Honda vehicle using the HDS or PGM Tester in Generic OBD II mode or a generic scan tool, you might not get the results you'd expect. That's because Honda vehicles actually use three different kinds of clear commands: DTC CLEAR, ECM/PCM RESET, and more recently, CKP PATTERN CLEAR. If you're using the HDS or PGM Tester in Honda System mode, the level of clearance varies. If you're using the HDS or PGM Tester in Generic OBD II mode or a generic scan tool, there's just one clear command. It clears all learned values.

Since all the learned values are cleared in Generic OBD II mode or with a generic scan tool, don't forget to do the idle learn procedure. And if you're working on a V6 model, don't forget to do the CKP pattern learn procedure, or you could wind up with a misfire DTC when there's really no problem. If you're working on a '05 Accord Hybrid, you need to be really careful here. Always turn the ignition switch to LOCK (0) after clearing the DTCs. If you don't, and you start the engine right after clearing, you could damage the IMA battery.