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Troubleshoot Help - Starting System

 
Old 01-21-19, 09:53 AM
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DCMCAggie
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Exclamation Troubleshoot Help - Starting System

*I'm going to try and explain the best I can in steps*
My 2011 IS250 will not start intermittently. I have already changed the starter, battery and alternator.
The time and distance traveled is not consistent to induce the gripe. Happens randomly. If I let the car sit long enough then I can start the car again with no issues. I can jump start car if jumping vehicle voltage output is high enough, but if its too low my car will still not start.

What I see inside the vehicle: When the gripe does happen, starter will not engage. I press the brake, start switch illuminates green, I press start button, fuel pump comes on, starter does not engage or make any other indication i.e noises, and after a few seconds the amber light illuminates on the start switch and ACC power comes on.

*Troubleshooting while gripe is present*
I got the system schematics and shot power at ST CUT relay, voltage across the relay coil Pin 2-1 is 12v, and resistance is 170 ohms. Moved to the STARTER relay and got 12v across pins 1 - 2 with an internal resistance of 207 ohms. Shooting pin 2 STARTING relay socket to ground I get 1.1 Ohms, however, resistance changes when I turn the cars lights on, and with full brights resistance increases to 9 Ohms, which I find odd. Now shooting STARTER relay pin 3 to ground I get a single digit Omage.

*System check while car is running*
I constantly get voltage across the ST CUT relay pins 2 - 1 (so its always energized), and thus I constantly get voltage at my STARTER relay pin 1-2. * Which seems odd because I would figure the ECM would cut voltage to the ST CUT relay once the car is started. Here is where it get weirder, if I pull the STARTER relay slowly while the car is running the car will die, and if I pull it quickly with a quick yank the car will sputter and pick back up and run normally. However, I lose lighting in my instrument cluster as well as displayed system information. I would assume that the starting system would not have a role in the car after the car is started.

Any ideas or if someone has knowledge of the starting system principles of operation it would be of great help. Thank you!!

Last edited by DCMCAggie; 01-21-19 at 11:14 AM. Reason: More description
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Old 01-21-19, 11:16 AM
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Starting system schematic
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