My 93 Cabrio has the 16 pin OBD-1 plug, with the red LED and push button. I also fabbed a blink light box per widely published info.

I'va had car for several months, no CEL. While swapping fan clutch I decided it would be a good idea to unplug the air pump, to prevent the pump from running and ruining; I live in a non-test area.

A few days later CEL came on.

On pin 3 I get codes 4 , 9, 18, 23, 26
On pin 6 I get codes 3, 8
On pin 7 I get code 3
On pin 8 I get code 1 (mericiful Mercedes gods, thank you!)

Is there a way to clear all these codes and start fresh, I am hard pressed to see how they would all be related the air pump. Or how a bunch of old codes would all "wake up" at once from the cobwebs of the ECU memory.

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91 300 TE 235K
93 Cabriolet 155K sold
92 300 TE 200K boneyard

Well, tried again with engine not running, just ignition "ON", with the built in blinker light, got codes 4, 10 and 26. This time pressing the built in button to clear and turning off key for 2 seconds, then wait 10 seconds, then crank semed to remove the CEL. So my blink light box or my timing may have been off on the reset.

Can I expect code 4 (air pump system ) to keep happening, is there some sort of functional test being run and the lack of pump clutch current or performance is noticed?

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91 300 TE 235K
93 Cabriolet 155K sold
92 300 TE 200K boneyard

I have continued to get a check engine light after several days of running clear, and the code returned is 4 blinks, which is air injection not working. I would guess that the ECU does a functional test of the air injection by some means on a periodic basis. Hooked pump plug back up and cleared codes.

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91 300 TE 235K
93 Cabriolet 155K sold
92 300 TE 200K boneyard

air pump only runs for a while at idle,never going down the road

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt