Just wondered if Prius 2 gave an error code when battery voltage too low. Mine is 12 sometimes dropping to 11.8 volts. Battery is about 5 years old. Replace?
Yes, a DTC (error code C1241) will be set when the voltage is low enough. If it still starts and moves, or if you have roadside assistance, you could continue to limp along with an older battery. Or just replace it. How many hours per week do you drive it?
Some of the ECUs have codes that can indicate low battery voltage, with the caveat that the codes are there to report the voltage arriving at the ECU in question. C1241 is a code from the brake/skid ECU complaining about low voltage measured there. The transmission control ECU can set some similar codes. Beware that when such a code is set, it very well can be telling you about a wiring or flaky-connector issue on the way to the ECU that is measuring the voltage. It is not guaranteed to be about your 12 volt battery (especially if the code gets set while the car is in READY, at which time the battery isn't in control of the voltage).
Or....... Purchase an electronic battery tester that you can use on all your vehicles to determine the true condition of your 12v battery at any time you choose. A good tester will pay for itself. I have an OTC model similar to this and use it on all my families cars, including extended family, friends and coworkers. I also test the 12v battery of every single car I work on, just to give the owner an independent analysis, since I have no dog in the fight regardless of the battery condition.
A weak 12V battery can cause problems in a Prius without previously giving an error code, so do not wait for a code before replacing the battery or following the good advice about testing.
In other words there is no code that explicitly tells you that the 12v battery is bad, but the C1241 can coincidentally inform you that the voltage is low. The instrumentation for proper 12v testing is not built into the car. A simple voltmeter helps a lot, a specialty tool can do even better.
In my experience more often than not a C1241 has nothing to do with the condition of the battery because most of the time this sets, the car is running, which means the battery is not the source of the 12 V supply. So if the battery is bad, then it is just that, coincidence. For the record, there is a battery low signal from the car. On startup, the MCL (master caution light) will flash momentarily. That is the only warning the car gives that is explicitly a low battery charge warning.
Thanks for the help. I think a battery dropping below 12 volts (I have a meter point right on the battery) probably is an indication to replace. We don't drive our Prius every day, so this means it won't receive a regular charge. When I do charge it from the jump point it behaves normally, accepting 8 amps initially then within a hour or so dropping to an amp or so. A vehicle on the other side of the garage (same temp conditions) shows 12.4 volts with no charging required. Although only a 0.4 volt difference, I think this difference is critical especially since the Prius sometimes drops to 11.8 volts. Seems like battery replacement is a smart move.
A traditional flooded lead-acid battery is scoring pretty well at 12.4 volts. An AGM battery as featured in a Prius is not so hot even at the same 12.4- you would want to see closer to 12.8. This is down to the difference in battery type.
Yes there is. Its a red triangle that flashes momentarily on the dash with all the other bulb check icon lights.. Its the only dash icon that does not light during bulb check boot up. It will only light if the 12 volt battery dips below (not sure what the exact go-no go voltage level is but suspect its 10.9 or there abouts) It flashes really fast once upon boot up but its very noticeable. Just flashed once like all the other icon bulbs. It does not log a code. Just a courtesy hey your 12 volt battery is dead. I saw it once when my 3 years old yellowtop died on me. Checked the battery with my voltmeter sure enough it was a goner. It was at 10.9 volts. Hard to miss its very bright red. Based on my 12 years of ownership the 12 volt battery driven regularly in my car seems to live at 12.6 volts. Never seen it go higher. Thats with 13.8 to 14 volt charging voltage.
