ToyotaViejo

Maybe a little off-topic, but I've been doing some work on my 4Runner that has prompted me to start, and in some cases drive, the thing with various harnesses and sensors unplugged.

The only time I've seen idiot lights come on at all were when my brake reservoir was actually low, and the battery light on cold mornings which I think was caused by a dying alternator.

Never seen the CEL come on (except at key-on in the startup routine), even after starting and driving with the TPS unplugged. I accidentally left the VAFM harness unplugged after replacing the alternator yesterday, and despite the vehicle stalling after idling horribly for a minute or two, no CEL.

I also found, during the alternator replacement, that what appears to be the driver-front wheel speed sensor harness (adjacent to the oil filter) was unplugged. No ABS/check brake light.

I know OBD-I is not the most advanced engine/emissions management system, but nothing seems to trip idiot lights.

brianh699

If you ran the vehicle longer I would imagine you would start to see codes register. Trouble codes half to have certain perameters met before the CEL is lit, ie dual trip detection, running above a certain speed for x amount of time, etc. FSM's have the driving patterns necessary to register each code.

scope103

Just look in the manual. http://personal.utulsa.edu/~nathan-b...85diagnosi.pdf The CEL is not some sort of universal telemetry system (neither is OBD-2), it signals specific, defined problems. I suspect you got no code from the unplugged VAF because you didn't (couldn't) give it enough time. Same with the TPS, but you could experiment with that.

ToyotaViejo

Interesting. Never read through that whole section before. The "high sensitivity" test mode looks worth some exploration.

Amazing how bare-bones this system is relative to my wife's '12 Civic. The computer on that thing can tell you what you had for lunch.

TNRabbit

Compare a computer from now to one from the early 90s......