How the 4A-GE ECU works

[JMR_AW11]

domi Wrote:Excuse the offtopic, but seeing you guys know what you're talking about i'd like to ask something. I recenty discovered my check engine light is not wired or not working or both, so in order to see if there are error codes i'm trying to route an LED directly to the ECU, to see what's what.

http://club4ag.com/faq%20and%20tech_page..._4A-GE.jpg
Going by the abovementioned link and a hint from jamie i was going to try linking the anode of the LED to the 'W' terminal and the cathode to the car's body, but then the question if i need a fuse arose. Would i need one and if yes - what kind. The diode i have is 5mm, 60mW, 2.6V forward voltage at 10mA. The forward current is stated 3.0VDC on the package, but from what i remember from physics class current was supposed to be measured in Ampers..? I really have next to no knowledge about electronics, so i thought i'd ask before frying my ECU... The engine is the 20v Blacktop from an AE111, it has been wired by the previous owner, so i have no clue if the job's good, but the car has been running before i bought it and the issues i'm having right now are very much weird to me. I outlined the trouble i'm having here:
http://www.aeu86.org/viewtopic/domis-gen...ead/t/4478
I'm sorry for splitting off the already posted topic, but seeing as ECU-adepts are discussing here, that'd be my best chance at getting their attention :wink:

AFAIK most W outputs are open collector so you would need the following circuit..

connect one end of a 1000 Ohm series resistor to +12V and connect the other end of the resistor to the LED anode.

Connect the LED cathode to W pin on the ECU.
That should work and it will pull about 12mA from the 12V with a really brightly lit LED... However, the W circuit also relies on a couple of specific ECU pins being grounded to chassis 0V.

This grounding happens normally with the stock wiring loom. Without these pins being grounded the W lamp cannot light.

Edit: Don't be tempted to miss out the resistor if you don't have one. The resistor limits the current through the LED. Without it you will destroy the LED and possibly the ECU transistor that switches the W lamp. You may even blow a fuse