Engine Check Light (or lack of it)

[beeker]

I have noticed the engine check light doesn't illuminate when you turn the key on (just prior to starter motor). Further more, if you run a diagnostics check, as per http://www.club4ag.com/faq%20and%20tech ... 0Codes.htm, again the light doesn't illuminate/Flash. Its an AE85 cluster, running a 4agze from a AE101 including AE101 ECU and loom.

I've looked up where the Engine Check light comes from the ECU (http://www.club4ag.com/faq%20and%20tech ... 090-91.htm Y Connector 22 pin, 5 WW Check engine lamp-instrument panel), and it appears to show a positive signal (a low 2/100 of a volt), including a variable signal when the engine is switched to diagnostics mode, but im unsure as to if this wire goes straight to the dash or somewhere else first ??
#### Update. It doesnt go to the dash, and is infact loose and unconnected ####

Trying from the opposite end with the AE85 Dash, the engine light appears to have permanent 12v, but no earth (ie it closes the earth to illuminate ??) which appears to be opposite to what the ECU is doing, and much higher voltage (12v versus 2/100th Volt). This is supported by checking the hand brake brake light, which works correctly on the dash, and again seems to have a positive feed, and will illuminate when earthed somewhere else.

I'm struggling with what to do next ?
Help !

[beeker]

Ok, I've now found that the ECU Engine Check light is not connected to the Dash at all. To do this presents a problem, as the ECU output is only 2/100th of a volt, and the Dash is 12V (and works off a Earth effect to illuminate the light).

I assume there is some type or relay that is used to step up the voltage here ?
And to reverse the positive ECU voltage into an earthing effect ? (excuse my terminology please)

Ideas ?? How does it work on the OEM AE101 dash from the AE101 ECU ?


or is my lack of electrical experience misleading me here !

[*84vvt*]

have you checked that the bulb has not blown???

[beeker]

have you checked that the bulb has not blown???

Yip, the 1st thing i did.

[*84vvt*]

ok
just had to ask

[*84vvt*]

Just had a look at the black top man
you should have 12v to the warning light on your dash
and the ECU earths it to turn it on
have a look
http://locost7.info/files/engine/4age_b ... bt8-fi.pdf
page 29 of 74

http://home.clear.net.nz/pages/phil.bra ... 20Outs.htm
this might help to
its in word

[beeker]

Just had a look at the black top man
you should have 12v to the warning light on your dash
and the ECU earths it to turn it on
have a look
http://locost7.info/files/engine/4age_b ... bt8-fi.pdf
page 29 of 74

http://home.clear.net.nz/pages/phil.bra ... 20Outs.htm
this might help to
its in word

Thx. I was suspecting that. Will look into further.

[beeker]

OK have solved it.

It was my lack on understanding on how it works. I was of the false belief that the ECU fed power to the dash to illuminate the light, where in fact it simply earths the fed coming from the dash.

The rouge power coming out of the ECU 'Check Light' cable (2/100th of a volt) put me off track.

Once i tracked down the wires for the dash/chasis loom, connected it up to the ECU loom, bingo.

Handy references were:
For the old AE85/86 chasis loom
http://www.club4ag.com/faq%20and%20tech ... 04A-GE.htm

For the new 4agze Engines Loom
http://www.club4ag.com/faq%20and%20tech ... 090-91.htm

blacktop manual on how it works (but good indication on toyota 4a geneic).
http://locost7.info/files/engine/4age_b ... bt8-fi.pdf

thx for your help.