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Yeah, the ECU supplies the ground circuit for the MIL. Grounding the "W" terminal really only checks the circuit up to the ECU. If the ECU is not powering up, then it will not supply the ground and thus will not light the MIL.
If you notice, my step 1 is checking the E1 wiring for ground. The E1 terminal / wire should have good continuity to ground. If it doesn't, the ECU will not power up.
Basically, if E1 has good ground and BATT has +12v all the time and +B and +B1 have +12v when the key is on, then chances are, its a bad ECU.
The other thing and the reason why I say "if everything checks out OK then check your ECU in another car" is cause the ECU also has fail safe modes that will cause it to shut itself down if there is a vital circuit is shorted to prevent damage to the ECU. Most of the time though, this will still light the MIL so chance are, either you have a bad ECU, or a problem in the E1 ground path circuit, or a power supply issue to BATT, +B and +B1
On a side note, if I happen to mention a circuit that you cant seem to find, PLEASE point it out to me. Most of my knowledge is with Supra ECU's and Lexus V8 ECU's and there are a few vital signals like M-Rel and IGSW that dont exist in the 3s and 5s ECU's. Toyota TCCS ECU's that use Stepper Motors for Idle Speed Control use these two additional circuits and they are vital to "power up" (well more so to "shut down" to reset the IACV back to its home position for the next start up). I caught myself in my last post bringing them up and then remembered that you wouldn't have those two... So again, if I happen to mention a circuit that you cant seem to find or dont have make sure to let me know.
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