Learning about newer cars & OBD2

[sketchers356]

So this is probably a total idiot question, but do cars show OBD2 codes without having a check engine light?

[Porsche-O-Phile]

They can show up as a "pending" code with a reader before the computer actually "throws" the code (which illuminates the CEL).

My $0.02 is that OBD-II is a horrendous PITA from an ownership standpoint. Yes, it can make things easier to diagnose, but it is (IMHO) a byproduct of vehicle design that is WAY too dependent on gizmos, doodads, sensors, wiring, circuitry and enigmatic black boxes. Yes, when things work on newer cars, they're amazing and put up numbers that were unattainable years ago (hp/tq/emissions), but it comes at a price - and that price can be AWFULLY steep if/when those little electronic thingamawhatzies built in China by the lowest bidder start to crap out after a few years of heat cycling and exposure to the elements...

Just something to consider.

My '01 MB is OBD-II and thus far (knock wood) it's been okay although I've had to replace an O2 sensor and more recently a secondary air valve. The upside of OBD-II is it tells you right away when these things crap out. The downside of OBD-II is it tells you right away when these things crap out, and if you're in a state that requires inspections (like CA), a CEL is an automatic fail. You HAVE to have it fixed (which can be big bucks depending...)

One more reason that I like my 944s and my 911. I'll decide what to work on, maintain and upgrade - and when. Not the government.

[sketchers356]

I am basically wondering if getting a cheap code reader would be a good idea for my BMW even though it is not having any CELs.

[Tobra]

hasndy thing tohave, for sure

[Porsche-O-Phile]

Can't hurt. A good reader will show you what else is in the computer, allow you to monitor lots of sensor outputs real-time, etc. Some of them even allow a limited degree of programming/tweaking, which is nice.

I still believe that OBD-II creates more headaches than it solves for owners, but if you're stuck with a car that has it, get a good reader. Can't hurt.

[masraum]

Originally Posted by masraum

I've got a scangauge ii. It does a ton of stuff, including reading and resetting codes.

The unit is small, 1"x4"x.75" roughly. I leave it plugged in all of the time and have it sitting in front of my gas gauge. It has the capability to display 4 "gauges". The Temp gauge in my car is essentially an idiot light with 3 settings, cold, normal and overheating. I get the exact water temp from the gauge. There are a bunch of other options as well. It'll also act as a trip meter including telling you how much gas you have left and how far you can drive before you're empty. It's pretty sweet if you're a nerd.

Trip computer, most of these options are available for today, yesterday, this trip or this tank

» Maximum Speed
» Average Speed
» Maximum Coolant Temperature
» Maximum RPM
» Driving Time
» Driving Distance
» Fuel Used
» Trip Fuel Economy
» Distance to Empty
» Time to Empty
» Fuel to Empty



digital gauges

» Fuel Economy
» Fuel Rate
» Battery Voltage
» Coolant Temperature
» Intake Air Temperature
» Engine Speed (RPM)
» Vehicle speed (MPH and KM/H)
» Manifold Pressure --- (not available on some vehicles)
» Engine Load
» Throttle Position
» Ignition Timing
» Open/Closed Loop

Scan Tool

» Reads Trouble Codes
» Reads conditions that set the Trouble Code
» Clears Trouble Codes
»

Turns off "Check Engine" light
» Tells you when vehicle is "Ready" to pass OBDII testing
» Make and store up to 10 rewritable special codes
to send to the vehicle computer

I posted this a few years back. I still keep it in my car, plugged in all of the time. When I go on long trips in a rental car I take it along. They have some new functionality since I first posted this as well. Now you can program your own gauges (lots of stuff on the Internet).

I really like mine.

[masraum]

I've had a bunch of obdii cars now, and never had the sorts of problems listed above. In my exp, obdii has been nothing but helpful, but I understand the thinking. I had a buddy years ago with an obdi car that had that sort of problem, and I'm sure there are folks with obdii cars that have had similar experiences. I love the state inspection process in an obdii car compared to an older car.

[Rick Lee]

I couldn't live without my code reader. I have failed emissions in VA and AZ with no CEL's and both times it was because of readiness monitors. You can only see those with the code reader and resetting them is next to impossible on a public road. Both times I was able to get through the whole reset procedure, my code reader is how I knew I was good to go back to the testing station and get it done before any more codes popped up. My car is the first year of OBDII, so it can be a little quirkier than later models. But AZ makes no exceptions for the early OBDII cars.

[john70t]

(take the following with a healthy grain of salt, as my edu'macation memory has lapsed).

The term "check engine light"(CEL) is only is used with OBDI(pre-1994-96).
1). OBD1 was a simple system and only checked components with the powerplant.
2). Vehicles usually only had one oxygen sensor before the cat.

The term "malfunction indicator ight"(MIL) is used with OBDII.
1). OBDII is a more intuitive(or intrusive and resistant to aftermarket changes if you will) system that actively tests components during operation. For instance, the computer will briefly open the EGR valve during cruise then look at how the oxygen sensors change. Some will briefly kill individual injectors or spark plugs.

2). Vehicles have two oxygen sensors to determine how well the catalytic converter is performing and if the short/long-term fuel curves needs to be adjusted.

3). After being unplugged, the OBDII has to complete a series of normal driving cycles(parameters) to pass a smog test.
This is sometimes a problem when getting a smog check right after a battery replacement. If the car hasn't been driven on the freeway "x" number of times, had wide open throttle conditions "x" number of times etc., it will return an incomplete result and the smog test will fail. Sometimes these conditions of operation can be difficult to find and complete.

4). OBDII uses both universal codes, which all scanners can read, and manufacturer-specific codes such as the several body sensors/computers used in an automatic convertible top.
The universal OBDII scanners won't read all codes, but good ones are reprogrammable to accept mfr updates.

[Porsche-O-Phile]

Big Brother.

[Rick Lee]

You can reset any CEL, but that won't reset the readiness monitors and you'll still fail emissions if they are the root cause of your problem.

[Zeke]

No, OBDIII is big brother.

[crustychief]

PoP is correct, it could have a DTC stored as pending without illuminating the MIL.

I am still trying to complete the drive cycles after replacing a purge valve on the Land Rover. It went in for smog and failed because the cycle was not complete. Another code came up after the first drive cycle for a small evap system leak, I hope I fixed that with a gas cap replacement.

[john70t]

OBDIII will have mandatory GPS to collect road tax(or save your children when you're upside down in a ditch with rising waters), RFID and Bluetooth to "share" the presence of all your toted articles, driving-habit memory for the insurance companies, remote kill, and remote unlock so the popo can rummage through your things while your at work.

On-star is a good start, tho.

[Rick Lee]

If you just care about making the light go out, AutoZone will do that for free. It might come back though, and it's always good to have a code reader. The reset procedure for a 993 is just ridiculous. There's just no way to do it without breaking a laws. I had to run a few stop signs and then put the cruise control at 55 mph in 5th gear on the nearby hwy., which is 75 mph. I was in the right lane for about 15 miles, getting passed like I was standing still. But after all the silly tricks I was fine for emissions.

[masraum]

Originally Posted by NotaBRG

Will the ScanGuage II do most of the things a VAG COM can do on my '99 A4?
ie can I reset the cel with the ScanGuage II or do I have to use VAG COM?

I'm not sure about vag com. I suspect you could search the net. I think that there is a forum or three for the scan gauge.

The scan gauge should be able to do anything that is necessary in an obdii system. I'm not sure if the Audi has anything extra that's proprietary to VAG or not.

[jpachard]

What do you guys recommend as a good code reader?

Cheers, James