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Q: Car starts, then stalls in one second.

asked by on October 04, 2016

My mom recently got her oil changed and had been driving for a while until suddenly one night her car would turn over and stall immediately. You push the button to start the car, and it'll start, but then die immediately. I tried revving the engine in the second that it's on, and it revvs high but still dies just as fast. There were even times it would die, then start revving again for a second, and die again. My OBD2 device gave me a P0685 code saying the following:

Powertrain - Computer and Auxiliary Outputs - ISO/SAE Controlled ECM/PCM Power Relay Control Circuit/Open

The dealer is trying to sell her on a mass airflow sensor and battery replacement for $600 at the moment. It seems like a computer issue to me, not a sensor. If you could give me some trustworthy advice on how to proceed, I'd greatly appreciate it.

My car has 35000 miles.
My car has an automatic transmission.

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Hi there. This can be a computer issue, but from the codes and the issue it sounds more like a voltage problem. If there is low voltage from a bad battery or a bad connection then the vehicle will act like this due to a communication problem. I have also seen the push button ignition switch fail on this vehicle and cause this. I always start by load testing the battery and checking all of the ground connection as these are the most common causes of this on your vehicle. If you find you are needing a second opinion on the work, or help with definitively diagnosing the issue, a certified technician from YourMechanic can come to your home or office and make repairs.

Mazda
Idling
Stalling
2014
L4-2.5L
automatic transmission
revving
6
P0685
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