94 Century (3.1) check engine light

[John B.]

Hi all, this is another one of my a-body wagons (I have 3 total). Lately the check engine light has been coming on and staying on for a few days, then it goes out and stays out for a few days. This has been ongoing for several months. Yesterday I had my mechanic check the computer for codes, but he said none were stored. The light wasn't on when he checked, but I thought every time it came on a code was memorized. What coud be causing the light to come on but not give a code? Thanks!

[85_Ciera_Rebuild]

What could be causing the light to come on but not give a code?

If I had a schematic, I could make a guess....but, if vehicle runs fine, place some duct tape over the check engine light.

1994, does that have OBD-II....you can buy one of those readers that gives real-time information for $50.00 or less these days.

If I had an OBD-II vehicle, I'd sure buy one..

[CieraSL92]

I wouldn't place duct tape over it, unless the car was already going to shit then maybe.

It's obd 1.5 I believe. 94-95 were transition years. It's supposed to store a code if it sets the light, yes. I heistate to say a bad ECM, but if it's not storing the code..

I would try disconnecting the battery overnight and just driving it to see if it reappears.

[SCREECH]

I'm pretty sure that '95 was the only year when the OBD-I connector was used but did not have the diagnostic pin, pin B. Have a look at your ALDL connector under the dash. The top right pin, pin A, is your ground connection. If there is a pin in the connector to the left of that then you can just use the "paperclip trick" to read your codes - turn the engine off, short these two pins, turn the ignition on but don't start the car. The check engine light will flash any stored codes.

[John B.]

The check engine light popped on again today so I had my mechanic hook up his computer and he said it shows EGR. The car runs fine, and these EGRs cost a fortune and they don't do emissions checks here. All I want to know is, if I don't change it, is it likely to hurt the engine or waste gas? Thanks!

[CieraSL92]

No. The egr is used to reduce cylinder temperatures (and thereby reducing NOX emissions) As a side product, if the engine happens to have spark-knock (noticable as a ping) I have heard the lack of it can cause it, however the knock sensor should hear that and back off the timing. If the engine runs okay as is and has power, and you have no emissions testing then fine.

[85_Ciera_Rebuild]

it shows EGR.


IT SHOWS...THIS DOES NOT MEAN IT IS BAD...YOU HAVE TO VERIFY ITS DEAD.

DON'T THROW PARTS AT A CODE...VERIFY THE PART IS DEAD FIRST.

Diagnosing Digital EGR Valves (http://www.wellsmfgcorp.com/pdf/Counterpoint3_4.pdf)

IT COULD BE A FALSE CODE...

[John B.]

That's very helpful....Thanks!