If you own a Toyota or Lexus hybrid and see C1241, C1310 or C1259 stored in your system, you're not alone. These codes often appear together and can confuse even seasoned techs because they involve both the brake system and hybrid control system.

In this article, we’ll break down:

• What each code means

• What causes them

• How they relate to each other

• How to properly diagnose and fix the issue

⚠️ What Does Code C1241 Mean?

C1241 – Low or High Power Supply Voltage

This code is set by the ABS/TRAC/VSC system when it detects that the voltage supplied to the brake actuator or control unit is too low (or in rare cases, too high).

Common causes of C1241:

• Weak or failing 12V auxiliary battery

• Corroded or loose battery terminals

• Poor ground connections

• Faulty or degraded brake actuator circuit

• Bad wiring or intermittent power to the brake ECU

🔧 Pro Tip: C1241 almost always points to low 12V voltage, especially after a cold start, long period of disuse, or aging battery.

⚠️ What Does Code C1259 Mean?

C1259, C1310 – HV System Regenerative Malfunction

This code is set by the Brake Control ECU when it receives an abnormal regenerative braking signal from the hybrid control ECU.

But here's the catch: C1259 is usually a secondary code, triggered by an existing issue elsewhere — often related to battery voltage or the hybrid control system.

🔁 How These Codes Work Together

In hybrid vehicles, regenerative braking captures energy during braking and stores it in the hybrid battery. The brake system and hybrid system must communicate seamlessly.

When the 12V battery is weak (triggering C1241), voltage drops can cause miscommunication between ECUs, leading to the hybrid system throwing C1259.

C1241 → voltage problem → causes hybrid regen error → triggers C1259

Additionally, if these codes are present, along with a P0A80, these C codes typically go away after a high voltage hybrid battery replacement.

🧪 How to Diagnose the Problem

Step 1: Check 12V Battery Health

• Use a multimeter to test voltage at rest:

  • 12.4V – 12.7V = good

  • 12.2V – 12.3V = borderline

  • Below 12.1V = replace battery

• Check terminals for corrosion and tightness.

• If voltage is good, do a load test to determine if it can maintain voltage under strain.

Step 2: Clear Codes & Monitor

• If C1241 and C1259 were both triggered, clear the codes and observe if they return after replacing or charging the 12V battery.

• Check freeze frame data to see which code occurred first — this can help isolate the root cause.

Step 3: Inspect Grounds and Power Supply

• Check ground straps near the brake ECU and inverter.

• Ensure the brake actuator is receiving stable voltage.

Step 4: Scan Hybrid System for Additional Codes

• If C1259 persists after fixing C1241, check for P0xxx codes like P0A80, P3000, or others tied to hybrid battery performance.

🧰 Repairs and Fixes

❓ Can You Still Drive?

If C1241 and C1259 are triggered without other active HV battery codes, the car may still drive normally, but you may notice:

• Loss of regenerative braking

• Reduced MPG

• Warning lights like ABS, VSC, or hybrid system

It’s safe to drive to a repair facility, but do not ignore it, especially if your 12V battery is aging or inconsistent.

✅ Final Thoughts

C1241 is often the root cause, and C1259 is the resulting cascade fault from voltage instability. Always start with checking your 12V battery and connections before jumping into expensive hybrid system repairs.

Regular maintenance of your 12V system in hybrids is more important than many realize — it powers the vehicle’s brain, and without it, even a healthy hybrid battery won’t help you start the car.