starts then dies with no mil.
when the car has been sitting cold the mil light will come back on when with key on engine off self test and then the engine starts spark ect. starts then dies,
Restarting with the Key on engine off and there is no mil indicator light self check. Starter cranks no start. no spark. No obd2 codes.

What sensor if any controlled by the ecm would short the mil light?

 

Are you stating the check light illuminates for a longer period of time when the engine is cold? The check light will always come on for a short time then go out.

Not all systems are monitored by the ODB2 system and the self test checks may require some many cycle failures before setting a code.

If no spark make sure the ign coils are receiving 12V at the black/orange wire.

With ign switch on one terminal of the coil always has 12V, the computer turns the injector on by completing the grounding circuit.

 

The check engine light will not self test when turning the key on cold or hot. There is no mil light at all. cranks with no start.

I checked for spark when no start but cranking. No spark was detected.

Occasionally when I turn the key on it will work and the check engine light will self test and the the car will start. good spark ect.

will check the coil voltage during no start no spark condition.

Thanks!

 

With the key on I have 13.6 v at the black/orange wire to coil #1, 2 ect. I am getting voltage to coils but still no spark, no mil light. cranks.
Since there are no codes what else could be knocking out the ECM's mil light and ignition function on the 94 1mz-fe engine?
I am thinking possible problem in the wiring between the Igniter and ECM or bad Igniter or a bad ECM? Dose anyone know how to test for voltage between these units? And is there any way to test the Igniter and ECM units themselves for faults without just swapping out units?

 

The check light lamp circuit is connected to the ECM and Gauge fuse. The Gauge fuse should be powered at ign on, the ECM grounds the wiring to illuminate the lamp. The light should power on when the ign key is turned on then after self check turn off.

The ECM receives 12v DC power from many sources.

One is the battery (white/blue wire) via EFI fuse, others of interest are the EFI relay and EFI fuse. This wiring is black/orange wire and has two connection points at ECM. These two connections power up the computer when the ign key is turned on.

Check for power at the black/orange wires (also power coils and injectors) when ign on. The ECM is behind the glove box, check for power at the black/orange wire inputs, again there are two connections to the ECM.

The white/blue wire stated above would have 12V.

There is no way to test the igniter, Toyota has a procedure where everything else is tested to narrow down the igniter as a problem. A bad igniter would not result in the check light not coming on when ign key being turned on.

Bad ECM's are not common although it has happened an ECM's failed to readout out trouble codes and need replacement, but the engine still ran.

Suggest you check power sources, wiring issues, ign key switch problems, etc before changing computers. Make sure the computer is getting 12V at the black/orange and white/blue inputs.

 

Thank you Joey! I will check the power sources as you described. I will certainly post my findings when I pinpoint the prob.

 

Checked all blk/or at ecm, coils, injectors good! checked battery EFI blue/wht and blk/or wires voltage. 12v all good! checked blk/or wire voltage at harness side ignition connector good! unplugged ignition harness connector and replugged mil light came on car started mil stayed on then it died. weird. will check for codes if any stored. Stumped! not sure if what I did by unplugging and replugging the ignition switch connector made it work mil/start. or if it even has any relation to the prob but I cannot duplicate it. so now is there a test for the ignition key switch function? How would the ignition key switch cause the ecu not ground the mil light and cause crank no start?

 

One end of the check light circuit connects to the ECU, the other to the Gauge fuse. If no Gauge fuse power the light will not come on. If the ECU has no power the electrical circuits of the computer will not work as designed. As with the injectors and check light, the ECU circuits turn items on and off by grounding a circuit like a switch.

The ECU/check light system runs a self test each time the ign key is turned on. As a result the check light will come on then go off once the self test is completed. When you reconnected the plugs perhaps the check light system was now working OK but once the self test was complete turned off.

The ign key system is two switches in one.

One circuit connects the battery to the Black/Orange wire the Ign fuse.

The other connects power to a host of fuses such as ECU-IG, Wiper, Gauge and Turn.

With ign switch on, check for power at these fuses or items.

Send a PM with email address will reply with wiring diagram.

 

Thank You fort the help. Yes I have the 94 1mz-fe engine controls wiring diagram from a book source. So here what I have come to. I have power at all points that should ect. The ecm fuse is good and have good power at wires to and from ecm circuits, since the ecm controls the MIL switch function and the symptom is that the MIL is shorting out (no ground function) and also there is no scanner communication with the ecm. Tried to read the ecm with the obd2 scanner and I just get a redundant error on the scanner (yes I know how to use a scanner. lol) I was able to trip and retrieve codes before when it would intermittently have mil ecu function so I know my scanner works. I did call Toyota talked to a service manager for info on testing my ecm unit, just to see what they would say, and the info i got was very helpful. They said, usually what they find is that when the mil light shorts out like mine has ect , it is the ecm. They don't open them up,test or repair the circuit boards inside the units ect. So i guess replacing the ecm is the next step. That is unless I could be overlooking something?

 

Yes, being unable to communicate with the ECM via the scanner tool can be caused by a bad ECM.

Used ECM are reasonably priced. Try auto salvage yards and Ebay. May sure you get an ECM with the exact same part number.