Originally Posted by MAXUM
Let me see if I can dispel at least some of this for you NB. I'll start by telling you that I used to work for Toyota as a tech (certified by Toyota and ASE as well for what that's worth). I'm no longer in the business, but still do plenty of wrenching on my own vehicles and family as well. I personally have one Toyota and two Lexus's. I won't own anything but...
The on board computer you have in your car must meet the ODBII standard which is a FEDERAL standard, not something that Toyota made up. The purpose of this standard was prior OBD systems were all proprietary and you did need a special scanner to easily read the diags, although there were ways around that as well by crossing the E1/TE1 ports with a jumper wire on the diagnostics connection and count the CEL (check engine light) flashes on the dash. The service manual would tell you what the code flashes stood for. ** EDIT ** This also is only for Toyota brand vehicles. Early generation EFI systems it was E1/T1, later it was E1/TE1.
Now ODBII introduced as I said a federal standard that ALL vehicles manufactured after 1996 have identical onboard diagnostics that all can be read with a single scanner, have the same plug interface and all use the same basic code library. Before this happened it really was a total PITA to be a "general all brands" mechanic. This allows for anyone to buy an inexpensive scanner to pull basic codes on any make or model 1996 or newer. It also helped out the independent shops from having to buy a scanner for every manufacturer and keep them updated every time a new model year hit the pavement. Believe me these factory scanners are big bucks. Now all manufacturers have extended libraries and codes that are brand specific but these are for more for diagnostics of proprietary systems. The basic ODBII federally mandated code library is mostly for throwing the CEL if a problem is detected in the emissions control system. For example I had a code thrown in my Lexus ES300 that was from the SRS library (supplemental restraint system - IE air bag system) and needed the extended Toyota reader to pull those codes.
It should be noted, if the computer is being sniffed for inspection.... you will fail if you reset the computer and immediately bring it down to be read. Before I get into why... if you want to reset the CEL, any over the counter ODBII scanner can do so. If you don't want to shell out the 50-100 bucks for one, instead of pulling the battery cable (which if done incorrectly can do damage to the electrical system) near the battery should be a fuse block, find the EFI fuse (usually a 15 amp) pull it for 30 seconds and plug it back in. Your onboard ODBII memory will be cleared and the light goes out. **EDIT** as a disclaimer, I know this works on all Toyota cars and trucks, other brands I have no idea. The CEL light will only go out after doing this if you are experiencing an intermittent problem, or the issue is not detected immediately. Some sensors that are in hard failure will immediately kick the CEL upon reset. Others like a faulty O2 sensor may not kick the CEL until it's seen several bad readings over a period of time.
On to why it's on and inspections. In order to pass inspection there must be no codes stored in the computer, a stored code equals a CEL on the dash. The computer must also be fully initialized and have gone through a full system data collection cycle which takes time from the point of reset. If you reset the computer and try to read it right away it shows several data points as "pending data collection" and if your car is being inspected and the computer is found in this state, you will not fail, but you will not pass. Rather they will ask you to come back later to re-sniff the computer or I should say that's what *should* happen. Time for full initialization of all data collections varies but usually if you drive about 50 - 100 miles or so that is enough but I have heard but cannot confirm some are based on start/stop engine cycles. What ever the case may be, you should be aware of this.
Now why is it on, well get the computer sniffed and you'll be able to find out what the problem is. Some auto parts stores will do it for free if you don't want to buy a scanner, Autozone comes to mind as a place that will scan for free, they also sell the scanners. Frankly the scanners are so cheap now it's almost silly not to just go buy one.
You need to be careful here because chances are the code being thrown is related to the emissions control system and although the car and even the gas mileage may seem perfectly normal the condition being flagged could over the long term do damage to the engine. For example - you may be running to lean in one of the EFI banks, a situation that otherwise would not make any difference in performance. Run in that condition long enough and you will do permanent and potentially catastrophic damage to the engine. I agree that the CEL can and does come on at times for bogus reasons, but if it keeps on returning with the same code something is wrong. Usually when I'm running diags on my own vehicles I'll pull the engine codes and then clear them out and wait to see if they return and if they do (50/50 shot) and how long it took for them to come back. I have at times driven for a while 2K miles or so to see if the problem will correct itself and kill the CEL or not. Then from there determine what needs to be fixed and address it.
Engines now a days are pretty sophisticated and attempt to think for themselves at times. If your Camry has a faulty sensor the computer can and will in the interest of emissions control may change the way the engine runs to compensate for whatever it thinks is broken or faulty.
If you think this is all bad the Government is working on the ODBIII standard which as it has been rumored will shut down your car if the CEL comes on and you ignore it for x amount of miles. It will also have a built in GPS unit and have the capability to output the health of your vehicle via satellite connection. The idea is to have your vehicle report it's having problems to your local stealership so they can call you on the phone to come in for service. Not to be out done here in the real commie states like California they are talking about outfitting the state police with readers that can pick this stuff up and actually pull over and ticket people to get their cars fixed. The DMV also wants access to this so they can black ball your registration renewal until repaired. Other states (of the typical liberal way of thinking) have expressed similar interest. I'm all for clean cars and keeping stuff in good working order, but this is way over the top if it's ever adopted, and don't think for one second is won't.
Um geeze I think I just blew about 45 minutes of work off to write this, back to the grind... NB I have no idea where you live but I'd be more than happy to sniff your computer and tell you what it's barfing about. It's takes all of about 2 minutes to pull the codes.
Had to make a couple edits just to make the statement that I know this stuff only works on Toyota vehicles, any other brand I have no idea. All my prior experience is with one brand, which is why that's all a drive.
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