C1241 Code with Freeze Frames - Seeking Diagnosis Assistance

Hello everyone,

I've been experiencing an issue with my Prius, and I'm hoping to get some advice. Approximately once a month, all the brake warning lights (both red and yellow) illuminate on my dashboard. This happens in two scenarios:

1. Parking Scenario: Most often, when I start the car while parked, the warning lights appear. However, if I turn the car off and then back on, the warnings disappear, and I can drive without any issues.

2. Driving Scenario: Occasionally, the warning lights come on while I'm driving. In this case, I stop the car, turn it off, then back on, and the warnings vanish, allowing me to continue driving.

The error code I consistently receive is C1241, which indicates either low battery positive voltage or abnormally high battery positive voltage.

I've collected three freeze frames related to this issue, which I've attached as PDF files to this post. While analyzing these freeze frames, I've observed the following:

1. The front right (Fr) wheel cylinder consistently shows an extremely low voltage (around 0.01 V) compared to the other wheels (which read around 0.45 V).

2. The Fr wheel consistently displays a different speed.

3. Strangely, the vehicle speed always matches the Fr wheel speed. How can this be?

In the most recent freeze frame, the vehicle speed and Fr wheel speed were both 1 km/h, while the other wheels showed 23 km/h.

4. Additionally, the voltage of the "Master cylinder sensor2" and the Fr wheel cylinder is equal (around 0.01 V or 0.03 V). Is this normal? It seems unusual to me, similar to the previous observation (see item 3).

As a layman, this is what I've been able to identify. Perhaps there are other anomalies I haven't noticed.

I plan to take my Prius to a reliable car repair shop where they're cooperative and willing to investigate the issue together. Unfortunately, the nearby Toyota shops haven't been very competent.

I'm seeking advice on what might be wrong with my Prius and which parts should be checked or replaced.

Any insights or recommendations would be greatly appreciated!

Thank you in advance for your help!

 

The 12V battery is fine, which is, of course, the first thing that should be checked.

My problem is that the malfunction is not constant; it occurs infrequently, about once every two months on average. There was even a six-month gap between occurrences at one point.

This inconsistency makes live diagnostics ineffective because the Prius generally works fine.

It seems like there might be a loose contact that only manifests under certain conditions, or perhaps a faulty sensor.

I read on a forum that replacing a wheel speed sensor might help.

However, I don't think the front right wheel sensor is necessarily affected. The suspect value in the freeze frames for the Fr wheel could be due to a general current flow issue in the entire system. But who knows.

So, my options are to wait until the error becomes constant, which is quite dangerous to drive with, or to preventively replace parts (but which parts?) and see if the error reoccurs. Alternatively, I could replug or clean some contacts (but which ones and where?).

What would be the best way to proceed?

 

Hopefully, you have read my post above. As a new user, my posts are moderated before they appear in the forum, which can cause a delay.

Could you please check my post above to see if you have already responded to it

Thank you!

 

Thank you very much! Your explanation is very clear and understandable.

However, I'm still unsure about how to proceed with the issue.

Should I continue driving and reset the error each time it appears until it becomes constant and shows up every time I start my Prius?