Hey guys, I don't know a whole lot about OBD, but I do know that OBD II stores codes but OBD I doesn't. My "service engine" light has been coming on and going off since I bought the car nine months ago. My personal wrench jockey told me that the codes can only be pulled when the light is on. Is this true? And if it is, can anybody tell me why the hell this light keeps going on and off? Other than the fact that "Catherine" likes watching me pull at my scalp? (I have no hair to pull out)

Michael

BTW, its a 95 LT1 A4. (most of you know that by now)

 

Actually, OBD1 will store "hard" codes. It is true that sometimes you may have a check engine light come on without the ECM storing the code if the event is not of sufficient duration (can't remember what that is). As long as the power to the computer hasn't been removed (battery disconnected, etc.) you should be able to pull the codes from it. You might also post in Scan and Tune. Hope this was of some help.

 

OBD I will store a code in memory. If the code does not fix itself, then it will be stored.

Next time the light comes on, cut off the car and then pull the code.

 

OBD I has two types of faults, Hard faults, which will be stored in the eCM and soft faults, which may not store a code. The transient check engine light you are getting sounds like it might be for EGR. The EGR can turn on the light, but if the light goes out on its own, it can dump the code out of memory.
Also, the codes are only stored in memory for 50 starts (as long as it doesn't reoccur). So, if it turns on the light and doesn't come back before you reach 50 starts, you won't see a code stored.

 

EGR? That's the engine computer right? Could there be something wrong with it? And if so, would it be something I could connect my laptop to it to correct? I hate to sound like an idiot, but I'm going to start doing my own wrenching so I gotta start somewhere.

 

EGR stands for Exhaust Gas Recirculation. The ECM (engine control module)calls for this under certain operating conditions depending on load and temperatures.

In many cases for a car in mostly stock trim an intermittent SES light is usually an EGR fault stored as code 32.

To check this quickly look under your driver side dash, you will find the ALDL or Assembly Line Diagnostic Link. Remove the cover and ground the A and B terminals (the top two on the right) with a paper clip bent into a U with the key OFF. With the terminals connected turn the key ON. The SES light will begin to blink. The ECM displays codes in two digits (every code is two digits) similar to Morse code. The first code you will always see is code 12. This indicates the ECM is in diagnostic mode. It will be displayed thus... one short flash followed by two long flashes or( . --). This will be displayed three times. After the code 12 any other codes stored in the ECM will be displayed in the same fashion. If it is the EGR the next code would be 32 0r (... --) also displayed three times before the next code.

An EGR fault is sometimes caused by the failure of the switch attached to the EGR valve itself. These are available from MAD for about $20.00.

 

Thanks for the reply!

 

Go buy yourself a Helms service manual. It will show you how to pull the codes from all the major sub-systems. SIR, ECM, CCM, ABS etc. And then how to step by step determine what is wrong & what to repair/replace. Will save you a ton of money on shops & keep from just throwing parts at things.

PS. You don't even need a fancy code reader or laptop, just ground the approp. pins on the ALDL connector under the dash to make the codes flash on your info. center area.

 

It's one of many things on my Christmas list!