2009 Shelby GT500. Engine would crank, start, die and threw up the fail safe engine mode message. Seemed that starter was spinning the engine a little slow. Tested the battery and it was weak. Installed a new battery and it would spin the engine fine, but it would not start and threw up the fail safe message again. Scanned it and it threw up code for control module failure. Erased the code and it fired right up. Several forums and two techs told me that a bad battery would not cause fail safe mode. Looks like it can. By the way, old battery was 8 1/2 years old.
Fail safe engine mode
- Thread starter dgc76
- Start date
Control modules don't like low voltage situations. During cranking the voltage may have dropped to 10 or even 9 volts causing the module to set a fault.
The fact that it does start but shuts off means something else. My 2021 Escalade had a fuel pump module failure and it would crank for a long time and start up just for a second but then shut off again. But it would only run for just a second or less which was just enough to let me put it in neutral so it could get towed. It's possible that the alternator might be completely dead as the battery might just have enough to start but I don't think so. Put cables on it let it charge and then start it. If it does the same thing even with the cables still connected it's likely a type of failure a new battery won't fix. Don't think a new alternator would either.
Weak batteries have been known to cause all kinds of bizarre faults in the modern computer controlled cars. Swapping the battery or jumpering to a KNOWN good battery is the first thing that I tell people to do if they're having unexplained issues in a car made from about 2000 and newer.
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