What Does C1849 Mean?
The ABS/stability control module has detected that the master cylinder pressure sensor reading is outside the expected range. This sensor measures brake pedal apply pressure to help the ABS and stability control systems calculate braking force distribution. The driver may notice an ABS or stability control warning light, and the system may disable advanced braking features while the fault is present.
Safety Warning
This code affects the ABS and stability control systems. While basic hydraulic braking should still function, advanced safety features like ABS, traction control, and electronic stability control may be disabled. Drive with extreme caution, avoid hard braking, and stay off wet or slippery roads. Repair immediately.
Common Causes
35%
Master cylinder pressure sensor has failed, producing a voltage signal outside the expected 0.5-4.5V operating range
25%
Wiring to the master cylinder pressure sensor is damaged, corroded, or has high resistance due to engine bay heat and moisture exposure
20%
Sensor connector has corrosion or contamination from brake fluid leaks near the master cylinder
10%
5V reference supply to the sensor is out of specification due to a module issue or shared reference circuit problem
10%
Actual master cylinder pressure is genuinely abnormal due to a hydraulic brake system issue
Diagnostic Steps
1
Using the scan tool, read the master cylinder pressure PID at rest (foot off brake) and with firm pedal application — at rest it should read near 0 PSI; under firm braking 1000-1500+ PSI. Readings of 0 or maxed-out values indicate a sensor or circuit fault.
2
Back-probe the pressure sensor connector and verify the 5V reference voltage and ground circuit — reference should be 4.9-5.1V, ground should be less than 0.05V.
3
With the sensor connected, measure the signal wire voltage at rest and while applying the brake pedal — it should sweep smoothly from approximately 0.5V to 4.5V with increasing pressure.
4
Inspect the sensor and its connector for signs of brake fluid contamination — brake fluid is an excellent conductor and can cause erratic sensor readings or shorts.
5
If the sensor and wiring test good, check the brake hydraulic system for proper fluid level, air in the lines, or a failing master cylinder that could cause abnormal pressure readings.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The ABS/stability control module has detected that the master cylinder pressure sensor reading is outside the expected range. This sensor measures brake pedal apply pressure to help the ABS and stability control systems calculate braking force distribution. The driver may notice an ABS or stability ...
The most common cause of C1849 (Master Cylinder Pressure Out of Range) is: Master cylinder pressure sensor has failed, producing a voltage signal outside the expected 0.5-4.5V operating range
Typical repair costs for C1849 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
This code affects the ABS and stability control systems. While basic hydraulic braking should still function, advanced safety features like ABS, traction control, and electronic stability control may be disabled. Drive with extreme caution, avoid hard braking, and stay off wet or slippery roads. Repair immediately.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to C1849 to identify the root cause.
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Quick Info
Category
Chassis
System
ABS / Traction Control
Difficulty
Type
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