C1246 on 2003-2009 Toyota 4Runner — Master Cylinder Pressure Sensor Malfunction
1 vehicles · 1 makes · $1,200-$3,000 repair
How to diagnose and fix C1246: most-reported vehicles
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Toyota 4Runner · 2003–2009
On 4th-gen 4Runners the integrated ABS actuator/brake master cylinder assembly (with electric pump motor and accumulator) fails internally. The pump motor or accumulator wears out so the pump never reaches pressure and runs continuously; owners get simultaneous ABS, BRAKE, VSC and TRAC warning lights, a loud continuous in-cabin alarm, electronic noise when braking, and a hard or sinking pedal with reduced assist. It is a safety-relevant failure and the assembly is one of the most expensive non-drivetrain parts on the truck. This is distinct from the brake booster/master-cylinder internal-leak issue: this is the ABS hydraulic actuator/accumulator unit.
Common Symptoms
- ABS, BRAKE, VSC and TRAC lights on together
- Loud continuous in-cabin warning alarm
- Brake pump motor runs constantly / electronic noise
- Hard or sinking brake pedal, reduced assist
- C-series ABS/brake control codes
How to Fix
First scan and inspect the wheel-speed (ABS) sensors and connectors, as dirty/damaged sensors mimic the symptoms cheaply. If the fault is the actuator/accumulator (continuous pump run, pressure faults), replace the integrated ABS actuator with master cylinder assembly - OEM 47050-60080/47050-60081 (4th gen) - and bleed/initialize the system with a capable scan tool. The part alone runs roughly $1,700-$2,300; remanufactured units are available cheaper.
Sources for this issue (2)
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C1246 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does C1246 mean?
C1246 stands for "Master Cylinder Pressure Sensor Malfunction." A Toyota/Lexus chassis code, shown in factory manuals as DTC C1246/46. The skid control ECU judged the master cylinder pressure sensor signal to be missing, erratic, stuck, or inconsistent with the stop light switch — this sensor converts hydraulic brake pressure into a voltage the ECU uses to know how hard the driver is braking. On most applications the sensor is built into the brake actuator assembly, not serviced separately. As a fail-safe the ECU disables ABS, traction control and VSC and lights the associated warning lamps; normal hydraulic braking remains, but the electronic assists are off.
What are the most common causes of C1246?
The most common causes of C1246 are: Failed master cylinder pressure sensor — on most Toyota/Lexus applications it is integral to the brake actuator assembly, Open or shorted wiring in the brake actuator / skid control ECU harness, Poor or corroded connector contact at the brake actuator or skid control ECU, Failed skid control ECU (brake actuator assembly), Low system voltage or a poor ground skewing the sensor signal, Stop light switch fault or misadjustment causing a signal-vs-brake-switch inconsistency. The specific cause varies by vehicle.
How much does it cost to fix C1246?
Repair costs for C1246 range from $1,200 to $3,000, depending on the vehicle and root cause.
Which vehicles are affected by C1246?
Au7o has documented C1246 across 1 vehicle models from 1 manufacturers: Toyota.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.