94 e320: no check engine light
 

I'm sorting through the issues on this 94 I bought recently, either I just noticed (duh on my part) or the check engine light has started to fail to illuminate with key on.

The engine harness has been replaced, dated 1999 no evidence of degradation.

Looking around, I found the OVP relay fuse blown, replaced it and that cured my ABS light. Non-ASR car.

The diagnostic LED is lit dimly all the time with key on, pressing button it get's brighter, but nothing blinks.

There is no ground or power on the CEL socket.

Car starts and runs beautifully fwiw, everything works but the cruise control, which might work now that I replaced that fuse and got the ABS light off.

The SRS light socket is completely MIA, I assume it was on and someone removed it, taped over the opening the cluster, and shoved the bulb holder down in the dash, I'm not overly concerned with it.

Everything else seems to work fine on the car.

I put a spare OVP in I snagged at the junkyard, no change.

Looking at the diagrams here: SG-Motorsports M104 Wiring Diagrams

I lack a component locator to track down the location of harness plugs.


I suppose my first step is to locate a pinout of the ECU and check for CEL output at the ECU?

It looks like the brown/white goes to N59 diag module(that I don't know where is) and the red/yellow goes to X81/4 that I don't know where is, then to X11/21 Diag test connector that I'm confused is supposed to be california specific or not. Red/yellow may also go to K1/2 OVP? I'm guessing CA models are the former with the N59 diag module. Is the CEL ground switched and full time hot?

I'm a diesel dude. Help? :)

press the diagnostic button for 3 seconds , then it will blink, after code is read via number of flashes pressing longer than 6 seconds erases code if there are more than 1 code , bring it up and press longer than 6 and cycle key when finished to clear instrument code light , 1 flash means no fault

the diagnostic module should be under rf footwell under the panel

Nope, diag LED is on dimly anytime the key is on, gets brighter when pressing button, no blinking or turning off at all happening. I wish it worked that way. :)

Not that I couldn't be wrong, but I thought I'd figured out that N59 diag module was the silver box with the securing knob on it under drivers dash left of steering column? Per this diagram: http://ww2.justanswer.com/uploads/PE/peterpete190/2013-03-08_161437_diagnmodule.gif

Far as I can tell, big yellow sticker under hood saying it conforms to all fed and cali smog, this is a california car with the OBD stuff.

very good yes thats it it has that twist knob on top,try unplugging it and rechecking, ive seen them quit working and need hard restart

Found the SRS light socket, good bulb, no light on key on. Just like the CEL.

I ordered an OVP just on principle.

Miracle of miracles, that appears to have done it.
Thank you!

Still no SRS light but I'll cross that bridge a little later.