Dash warning “stop car turn off engine do not drive, brake failure”?

Tiny
GARRY MARTIN
  • MEMBER
  • 2012 HYUNDAI SONATA HYBRID
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 186,000 MILES
After backing out of the garage we heard a slight grinding sound for just a moment. Then a message appeared “stop car turn off engine do not drive. Brake failure”

The Code C1237

Active Hydraulic Booster

C1237 Primary Pressure Sensor-Signal


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Friday, June 2nd, 2023 AT 7:52 PM

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Tiny
STEVE W.
  • MECHANIC
  • 12,824 POSTS
Service info says it could be one of the pressure sensors or the hydraulic control unit itself. However, the diagnostics are a lot vague. Basically, it says to use a scan tool and look at the pressures the pressure sensors show with no brake applied and then with your foot hard on the brake. Then erase the code and see if you can make it set under the same conditions. If the code returns it says replace the sensor, however it also says that to verify it is the sensor you need to use a "known good hydraulic control unit" (IE a new spare) to test with. To remove the unit, you remove the air cleaner ducting, then use an extractor to remove the brake fluid from the reservoir, then disconnect the wiring harness and the brake lines from the unit. Replace it and tighten the lines down. Now use a scan tool and bleed all 4 brakes to remove the air. Bleeding cannot be done without the scan tool, and you will need to use it to verify the repair as well. They do not show any information about the sensor itself, so I believe it is integral to the module.
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Friday, June 2nd, 2023 AT 8:26 PM

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