Hi all. On my '93 500SL there is a problem with Diagnostics. When I first imported the car to Canada, it had to have a fairly comprehensive safety check. Prior to the safety check, it had a code, which I managed to clear. When the tester took the car on road test, he went to an "expert" to check the codes. Since that time the plug is inoperative, so don't know what the "expert" did. It has both the positive and ground feeds, but using the home made blink bulb tester, which previously worked, it has no response. Any thoughts on where I should look ? Thanks.

 

the older diagnostic plugs and circuits look simple but are actually difficult. What you need to do is read the very comprehensive documentation on the circuit in WIS all else is FUYAA

 

Dale1941, start by verifying that your diagnostic port has +12V (ignition on) and chassis ground. In the 38-pin OBD1 socket they are pins 3 and 1 respectively. In case you have the older 16-pin socket, terminals 16 & 1.

 

Yes, these pins are connected. (38 pin connector)

 

Don't know what the acronyms mean.

 

So your tester's LED is lit but you get no blinks from any of the test connector pins - right?? Try give us some more clues.

 

No, the LED doesn't light up. Don't really have more information to give.
Thanks for the responses.

 

Well, if you have 12V and ground present in the diagnostic socket but no test light, the primary suspect must be your home made tester.

 

Thanks Pazo. I guess I wasn't explicit enough in my last message. The LED lights up by pressing the momentary switch (red - black wires) ,but plugging in the yellow diagnostic wire does not give a blink code when the momentary switch is pressed.
Dale