CEL (Check Engine Light) on my Honda CIvic FD2 [FIXED]

It was the end of another long day at work. It had been raining heavily almost every evening for the past couple of days now. Fortunately, the roads that I travelled were relatively free from puddles that made driving dangerous by causing hydroplaning (at high speeds) and masking potholes (like my recent disaster at Penang). Speaking of disasters, the latest one to knock at my door came about as I turned my ignition key that evening.

The check engine light came on, along with the VSA and one more indicator. I shut off the engine and restarted a few moments later. The other lights were gone but the check engine light remained. The K20Z2 under the hood purred softly and smoothly as normal, idling at the usual 600-700 RPM with no sign of engine trouble. The exhaust hummed normally as well, with no sign of smoke or sputtering. Driving off slowly, there was really no sign of abnormality, other than the glaring orange triangle of the CEL indicator in the dashboard display. To be safe, I made sure the revs did not rise above 3 kRPM, which was not that easy, given my FD2 could easily rev to redline, especially in the lower gears.

I made it home without any drama. The next morning, the CEL was still on, thus I decided to drop over to my Honda Service Center of choice, GS Tay Auto Muar, to check it out. Don't want to wait until the REAL cause of the CEL shows itself....

There was still no sign of any mechanical trouble as I took a slow drive to Muar, some 45 minutes away from home. Upon my arrival, the friendly staff greeted me as I calmly and clearly explained my predicament.

They started to check out my car, as I sat in the waiting lounge, typing the first part of this post (up to this point, actually).... :)

Fast forward a couple of hours. They finished checking my car. Unfortunately, they couldn't figure out what was the actual root cause. All they could do was reset the ECU (which turned off all the warning lights). Sigh. I guess I would have to wait and see if those warning lights come on again.

I didn't have to wait that long. The next morning, the family CEL and other warning lights lit up again. I shut off the engine and popped the hood. I scrutinized my engine bay, not really sure what to look out for, but the Engineer inside got the better of me....

Out of sheer luck, I noticed that the metal ring that sealed the air intake hose after the MAP (or was it MAF) sensor was loose. This was the hose where the other end was connected to the throttle body. I was skeptical that such a trivial "screw loose" case could be the actual cause for this. Anyway, no harm in fixing this, so I tightened the ring and started up my engine once again.

I was half-expecting to see the warning lights once again, but they never came on. I repeatedly switched off my engine and restarted several times - still no more abnormality. That was it - I solved the problem! [UPDATE 26 Nov 2011 - still no recurrence up to now, so I guess this was the actual root cause]

Somehow or rather, the poor seal caused by the loosened air hose must have let in additional air than the sensor could detect (since the loosened coupling was after the sensor). That must have confused the system, and thus generated the slew of warning lights. I have no idea how the VSA and "!" systems are affected, but for whatever reason, they are now gone as well.