Vehicle Info:

• Model: 2016 Skoda Octavia

• Engine: 1.4 TSI (EA211)

Symptom & Behavior

• Symptom: Red brake warning light / error on dashboard, stiff brake pedal (complete loss of vacuum assist).

• Frequency: Occurs roughly once every few hundred kilometers.

• Recovery: Braking feel returns to normal/soft after the throttle is released and brake pedal pressed.

Trigger Conditions

The issue occurs ONLY when driving uphill, and strictly under one of the following two conditions:

• Maintaining a steady / constant throttle input.

• Cruise Control is active.

Non-Triggering Conditions

• Driving on flat roads or downhill.

• Uphill driving with dynamic, varying, or heavy throttle inputs.

• Engine idle or routine city driving.

Completed Diagnostics & Results

• Check Valve (Manual Cold Test):

  • Line removed completely and tested manually at room temperature.

  • Result: Free airflow from booster side to engine side; 100% blocked from engine side to booster side.

• Brake Booster (Servo) Vacuum Retention Test:

  • Engine idled for 15 seconds, shut off, and left off for 5 full minutes.

  • Result: First and second pedal presses were soft; pedal stiffened on the third press.

What say the Error Log ?

I scanned it with a basic OBD2 code reader, but no fault codes came up. Unfortunately, I don't have access to VCDS, OBDEleven, or a professional-grade scanner to check the deeper ABS/brake module logs.