2001 Prius Error Codes and loss of Acceleration Problem

Hello, I'm wondering if anyone could help me diagnose a problem with my 2001 Prius. I was driving it on the highway when suddenly the hybrid system warning light and the main battery light, along with the check engine light came on. I pulled over, turned off the car, and turned it back on. The main battery light error cleared but the Hybrid System warning light stayed on as did the check engine light.

I took my car into the dealership and they told me that the 12V battery was probably low at some point but that they didn't find any problems.

The error codes that came up were: C1215, C1241, C1259, C1521, C1522, C1558, and C1559.

As of this moment, the car seems to be driving normally.

How old is the 12V battery? If more than 4 years old I suggest that you replace it now.

DTC C1241 is definitely produced by abnormal voltage from the 12V battery. The other codes might stem from that root cause.

I hate to ask - but how many miles do you have on the car, and has the HV battery ever been replaced? Hopefully it is the 12V battery, but I can't help wondering about the HV.

Hi new poster. The title mentions loss of acceleration, could you describe that a bit more?

Beyond replacing the 12 volt battery (as suggested) and making sure that its electrical connections are free of corrosion, there are some other light maintenance things to consider doing. They've been described at Prius Chat before.

Thanks for all of the advice. The loss of acceleration was more of just not being able to accelerate anymore, but the car didn't jerk. The gas pedal was completely non-responsive and the speedometer disappeared off of the dash. The car didn't slow down but it wouldn't accelerate anymore.

Do you do your own maintenance or have a mechanic handle it?

I would like to suggest having the ground wire connection at the frame cleaned and both 12 VDC battery terminals. It sounds like an intermittent 'open' and creeping corrosion can cause this symptom. But I agree with the others that your 12 VDC battery sounds . . . suspect.

Areas with high humidity and salt-air exposure can often develop corrosion that over time, insulated the conductors at a bolted connector. Seattle sounds likely to have both high humidity and opportunities for exposure to salt water, air.

Bob Wilson

I have my mechanic do the work on the car. The problem is that they don't know all that much about hybrid cars so they aren't really positive what is going on. The problem happened again and they rescanned it, and he came up with the P3100 code also.

DTC P3100 is logged by the hybrid vehicle ECU, and indicates that ECU has a malfunction. Sounds like it's time for you to visit your local Toyota dealer service dept for help.

Has your car suffered any accident damage in the recent past?

Some information codes associated with P3100 indicate an internal ECU problem. Some do not. P3100 can set for many reasons. The repair manual documents some of these reasons.

The most logical step would be to measure the open circuit voltage of the 12V battery at rest (vehicle turned OFF, key out of ignition).

Of course we can hope that the 3100 subcode will point towards a simpler, external cause, but the descriptions of almost all its subcodes begin with "HV ECU internal error", do they not?

Of course, if not done yet, measure the "12 volt" battery voltage. By cleverly putting the meter probes at different points you can see if there is voltage drop due to corrosion at various connections. Your man with the meter can also determine parasitic drain on the battery with the car at rest. Much more than 40 milliamps would indicate something else is amiss, and possibly draining your little battery. The inrush current is greater than 10 amps, so shunt the meter when you connect it and save buying a replacement fuse

That's correct. But in my opinion, the great majority of P3100 codes are not caused by a faulty HV ECU.