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Confusion about which battery cranks engine

Created September 17, 2007, at 4:40 pm by bg1811

I was under the impression that the 330v (or whatever it is) batteries are used to crank the engine. Yesterday afternoon I left the parking lights turned on. This morning the engine wouldn't crank, the car was "dead." I had to jump the 12v battery to start the engine. What am I not understanding? This is on a 2007 Mercury Mariner.

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GaryG
Senior Member

4 years ago

The 330V battery cranks the engine over, however, the 12v battery must have a charge so the PCM and TBCM can send a signal from the 12V battery system to the TBCM for this to happen. In other words, both batteries must have enough charge.

Once you restored the PCM (brain power) with the 12V battery and the traction battery control module (brain power), power could be sent to MG1 to start the engine. The PCM can then send fuel and spark to the combustion chamber to start the engine.

GaryG

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