2011 Golf No Start Mystery

The car is my wife's 2011 Golf TDI. Last Monday morning she gets in the car to go to work. Car sits in unheated garage all night. When she tries to start it, she turns key expecting the usual dash lights to come on then go out. She said she waited about 2 seconds for the glow plug light to go out. Then when she turned key to fire the engine no crank no start but all the dash lights, interior lights, even the headlights started flashing on and off. She gets me and I try a start. Same lights flashing. I'm thinking, okay dead 2 1/2 year old battery. Connect my battery tester to the battery and it tells me battery has a full charge ?? I decide to put my booster cables on it anyway. Start my car sitting right beside her's and make the connections. Get in her car, turn key, no flashing lights this time. She cranks and fires right up. Let it run for about 5 minutes then shut it down. Connect my battery tester again and do a load test on the battery. Shows in the green for 600 CCA. Her battery is the original 640 CCA. So battery passed the test.

Doe's anyone have any suggestions as to why it didn't start, then did with a boost ? No CEL and no DTC's. Car has started fine every time since this event. I'm thinking the chip in the key lost communication with the ignition cylinder causing the no crank/start. But then why would a boost fire it up ? All suggestions welcome.

Loose cable connections possibly? Grounding connections are very important. I've gone over mine before and cleaned up connects at the starter and the ground behind the battery. Just a thought.

TNriverjet said:

Loose cable connections possibly? Grounding connections are very important. I've gone over mine before and cleaned up connects at the starter and the ground behind the battery. Just a thought.

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Thanks for the suggestions TNriverjet. Will look at the grounds more closely. It's behaved fine since I got her fired with a boost last Monday. I've been told about a gear position interlock switch that could have caused this. Kind of like if the gear selector wasn't fully in Park. Makes sense. But would that cause every light on the thing to flash on and off numerous times with the no crank no start. Was that a sign from the car telling me this ? My VW dealership diesel tech. didn't have a clue when I explained it to him. I don't think he's my tech anymore.

Do you have a VCDS cable or at the very least a code reader?

If you have a VCDS cable, plug it in and see if there are any fault error codes that pop up.

amstel78 said:

Do you have a VCDS cable or at the very least a code reader?

If you have a VCDS cable, plug it in and see if there are any fault error codes that pop up.

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No VCDS. But Christmas is just around the corner. Would also need a laptop. Her Golf has run fine since.