Ok, i pick up this 97 Sc300 about a month ago. it would not start.. No crank no start but everything else works. replaced the starter, battery, spark plugs and wires. checked and replaced all fuses and relays. replaced the ignition switch. it wont start from the key. i do drive it daily. i start it from ig relay slot, by giving pin 5 12vdc. anybody understand whats going on here. im thinking the ECU is fried?

 

I assume when you say IG relay .. you refer to the Starter Relay.

Providing 12v to pin 5 is giving power to the starter solenoid thus activating solenoid that engages the starter.

It is a wiring issue or your Park / Neutral switch has failed. That starter relay circuitry is not controlled by the engine ECU so I doubt it is your ECU now that you say your car runs fine except you can't start it with the key. The coil of that starter relay is controlled by your theft detterent ECU. That is a possible problem area. But you can rule that out by applying the 12v to pin 1 of that relay . If the car starts then the theft detterent circuitry is fine.

Then work yourself backwards. I assume you have the wiring diagram that is why you were able to get into that pin 5 of the starter relay.

 

sorry ive been banging my head over this for a while so yes i mean starter relay. i keep coming back to the anti theft device. i have no code or the owners manual. ill try that thanks. ill post a update in a few hours.

 

one end of the coil of that starter relay goes to the theft detterent ECU .. so if you apply 12v on the other end of the coil , activating the relay switch (power goes to solenoid of starter thus starting the car) , then the theft detterent ECU is not your problem.... then go backwards on the wiring diagram .. your Park / Neutral switch or wiring issue that provides the 12v should be checked