Reading Codes on 1990 300E
 

Have been having an intermittent (not very often) check engine light on the 1990 300E I just acquired. Since it's OBD1, Autozone and the like can't read the codes for free. I had hoped the car would have a built-in pulse counter so I could read the codes that way, but I don't think it does. All I see by way of a diagnostic module is a little black box with holes numbered 1-16.

I've been doing lots of searching on the forum but still not sure what to do. Can someone point me in the right direction.

Have spent virtually all my time over on the diesel forum....this is my first foray over to the gasser side! :)

If there isn't any LED & pushbutton on that diagnostic connector?
then the ONLY way to diagnose a problem is by watching the duty cycle.

Check engine light on a non-California car is for lack of O2 sensor activity.

What is meant by "watching the duty cycle?"

Are you saying that that's the only possible cause on a non-CA car (which this is)?

The Baum book says you can read some flash codes on a 1990 300E, CA version or non-CA, probably just pins 3 and 14, but that's better than nothing. You'd need to build the flash code reader with Radio Shack components, around $10.

For a non-Calif 1990, you should have the 16-pin connector over by the battery. Most of the pins are blank, but pin 1 is ground, pin 3 is the CIS, 6 is SRS, and 7 is AC.
Do a search here for "error code reader and reset tool" or similar subjects.
There is one I found by a fellow named WES that outlines the little box with a switch and LED that you can easily build. Plug it into the connector and record flashes. Flashes vs codes are also referenced in the thread. I built one awhile back, and it works great.

One comment - the CEL will not light up in most cases, even if you have a dead sensor or other major problem. The only time it will light is if the problem is severe enough that the system cannot still correct the fuel mix to a normal range. However, by reading the codes the problem will show up.
I've disconnected various temp and throttle switches at times, no CEL - as long as the system could default around them and get the fuel trim back to semi-normal.

DG

Try this thread in the DIY forum - I think that's how i tracked down the diagnostic flasher instructions.

560SL diagnostic port/tool - PeachParts Mercedes ShopForum


DG