gttheo

OK a quick reprise of CA smog laws reveals they're only supposed to fail an OBD1 car if the check engine light is ON. The fact that it did not turn on when expected should not have been the sole reason to fail the car, if I'm understanding the letter of the law correctly. If that is correct then he's just taken it to the wrong shop, maybe someone can confirm?

Also it seems there are stricter laws in Santa Barbara than San Diego county. Would it benefit to have the car tested in SD where I reside?

993_540

The CEL needs to be on at startup, otherwise someone could just disconnect the bulb to get around the light being on after start.

just confirmed mine comes on



dave
95 C2
03 540i6
84 380SL

gttheo

Right, but CA law seems to only specify that the light not be on.

jay@EZimmoblock.com

Not sure if 95's do this but on my 97, if the bulb is burnt out (or removed) the ECU will detect it and throw a code.

pp000830

Hi Gttheo,
It is highly unlikely it is the Motronic ECU, more likely it is the lamp, its socket or the plug to the gauge that contains the bulb.
Use some spray electronic cleaner to clean the plug and socket behind the gauge that has the bulb, it is the Oil temp/Pressure gauge..
Also, inside the gauge should be checked for poor solder connections.
Be aware the socket connections for the Check Engine Light (CEL) are very delicate and should be looked at very closely for connectivity. Also, the bulb should be checked with an Ohm meter. Once reassembled the gauge can be checked looking for the presence of the bulb's filament resistance at the bulb pins on the back of the gauge using an Ohm meter.

If the Bulb, its mounting, and the connections at the gauge check out one needs to attach an Ohm meter directly to the pin on the ECU plug that powers the bulb under the seat to the plug behind the gauge to check for connectivity. If this checks out a voltmeter should be attached to the wire at the ECU plug to check for the presence of voltage from the ECU to power the bulb. One needs to verify the picture below matches the actual ECU plug on the car as I believe there are two different ECU plug versions involved depending if the car is OBDC-I or OBDC-II. Both pin-out versions are readily available doing a google search on the internet,
Also below I found what looks like the pin-out to the plug behind the dash that leads to the ECU so continuity to the ECU can be checked. This drawing can be verified by simply looking at the CEL bulb connections to the socket internal to the gauge.
Finally here are instructions on how to remove the driver's seat to get to the Motronic ECU. There is a security shroud covering the controller that will need to have it's mounting fasteners drilled off. Seat Removal
The hardest part of the whole job will be drilling off the security fasteners from the shroud followed by removing the seat, the actual testing is easy. If you don't have a Volt/Ohm meter a $7 one at Harbor Freight will work just fine.
If you don't know how to use a Volt/Ohm meter shoot me a private message with your phone number and I can walk you through it or I am sure there is a video on Youtube covering the subject.
Good luck with this.
Andy

Chuck W.

Damn Andy..... you are the best. Nice reply to the OP!

gmorat

The light has to be operational and it's proven to be when the ignition is turned on and it lights up. Otherwise the bulb could be blown or disconnected to try and hide a fault.

Trying to make an argument to the tech that technically the car is meeting the requirements to the letter of the law seems like a losing proposition to me but maybe?

I would try and figure out why the check engine light isn't coming on personally.

Lorenfb

The DME ECM provides a ground to the bulb.

gttheo

Thanks all for the advice, it's been invaluable. We won't get to check the light until next week. Very much appreciate the validation that a bad ECU is very unlikely here.