How long does the blazer keep a code?

[Sen Sen]

This morning my 94 (w)blazer gave me the SES finger right on start up. I waited for it to warm up, drop it in gear and about 15 seconds later it goes away.

The engine ran fine, drove it about 3km, parked it.

Ten hours later I start it up and the SES light comes on again, same thing....I waited a little and it turned off (about 2min)

I get home, plug in the code reader and it gives me code 12(everything OK)

I was under the assumtion that the computer holds the SES code for approximatly 24-48hours? if not...how long?

Should I worry about this?

Could the reader be wrong? it's always worked before.

[wolfox]

If memory serves correctly, there are two kinds of DTC codes set. A "hard" and a "soft" code. A soft code may or may not light the SES. A Hard one will will definitely light it. However, a hard fault will remain on until the problem is fixed. Soft codes can be stored and I do not think that they go away, just get overwritten in time. I am not positive about this, as my memory is quite foggy on this. I am sure someone else can speak up to clarify. However, since the code comes and goes seemingly randomly? I would just make sure all the plugs, hoses and sensors are tightly connected and clean under the hood. You may have an intermittent fault that just goes away when engine vibes wiggle a loose connection for you.

[mike2004tct]

This is a puzzle to me also.

A co-worker has a '00 Blazer that stored injector misses for over two years without turning on the SES light until the day he took it in. The codes listed by the shop were pages of the same injector misses.

On another car ('96 Sunfire) I had SES lights due to a charcoal cannister overflow. I disconnected the battery for 10 minutes and the codes are gone (My understanding here is this is VROM- volitile read only memory- that disappears or erases when you remove power). There is no back-up battery in the ECM that I know of, like the clock battery in your computer)
Perhaps I've missed some facts here, but the basic idea seems to work in my world. Plus that, the ECM is a logic-based operation, which makes no logic at all. (Jumbo shrimp)

[Sen Sen]

It just happened again while i was driving home today, I pulled over right away and pluged in the reader... still reading code 12.
Check all my connection and everything looks fine.

I'm going to the shop tommorrow to get it scanned by another reader

[Sen Sen]

The shop had the same code come up.(12)
I reset the ECM and I still seem to get the SES light once a day now.(randomly)

Any advice guys?

[wolfox]

Only thing that I can conjure up to recent memory on the whole ordeal that would do that to your truck:

Loose connection to your MAP sensor (if it's just not simply dirty) or a sticky/hanging EGR valve. Both will light the SES while the truck's in motion, but it "resets" itself after you shut the engine off for more than a minute.

[BlazerBoyLT98]

Can't find anything on that. My cousin had a Ford Bronco and his kept the codes for 450 miles! So even if the error corrected itself or was corrected you needed to drive it long enough to make it clear to pass inspection. That sucks

[Sen Sen]

It ended up being a faulty air/temp sensor, just had it replaced.
A mechanic I spoke with told me that the OBD I system does not hold a code at all and that you can only read the SES code when the light is on at the time?
He also said that the code can be read while the engine is running?
Is this true?

[wolfox]

Yes, that is true, but you need a special thingamajigger to repin the output so a hand scanner or tablet PC diagnostic computer can be used. My mechanic uses the latter with great success, he even started the engine to obtain the code details and monitor stream data.

[mike2004tct]

Originally Posted by wolfox

Yes, that is true, but you need a special thingamajigger to repin the output so a hand scanner or tablet PC diagnostic computer can be used. My mechanic uses the latter with great success, he even started the engine to obtain the code details and monitor stream data.

I searched "thingamajigger" at all the parts Cos, and couldn't find it.

Please post a pic.....

[Sen Sen]

Originally Posted by mike2004tct

I searched "thingamajigger" at all the parts Cos, and couldn't find it.

Please post a pic.....

further more how much does this complicated "thingamajigger" cost?
and can I also find it under "thingamabob"?

[wolfox]

Hey now, jokes are my department!

Seriously though, the device my mechanic used and then let me drive around with to capture data was so expensive, I could have 4 of my trucks for the price of one of these things. However, there is a product available over the counter at Autozone that will extract the codes even from a '95 with the bastardized computer for about $350. The device my mechanic used was simply an OBD-II plug with a socket on it's side. Into the side of the socket, a pin card was placed that re-routes the pins from the 16 pin header and pulls the codes and data stream in realtime from three other subsystems the ECM monitors and shares the data bus with because though it *looks* like an OBD-II plug that a scantool would fit, it does not talk OBD-II at all. The product name for us laymen is: (Quick Google Search and stock Veriication at Autozone...)

Actron Super Auto Scanner OBD 1 & 2 kit
Autozone and Actron Part # CP9150
Price: $379.99

It beats the snot out of trying to get the orange and grey plastic touch sensitive display tablet PC with all of the harnesses, cable and pin adaptors for over $15k. :22yikes: