Error Code P050F is defined as Brake Assist Vacuum Too Low. This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made from 1996 up to the present. It’s particularly common, but not limited to vehicles from Buick, Cadillac, Chevrolet, Ford, and Volkswagen. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

When this code is stored, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected an incorrect signal input coming from the VSS (vacuum brake sensor), indicating an insufficient vacuum condition at the brake power assist booster.

There are many different types of brake power assist system, and Error Code P050F only applies to vehicles with engine vacuum and a vacuum brake booster.

If the PCM reads that the vacuum level of the brake booster is outside its set parameter, then the Error Code P050F will be set, activating the Check Engine light.

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to vehicle’s memory system. Other common symptoms include:

  • Hissing sound when the brake pedal is depressed
  • Brake pedal requires increased effort to depress
  • Vacuum leak causing engine drivability issues

In some cases, other MAP (manifold absolute pressure) error codes may also be present.

Possible Causes

  • Damaged vacuum brake sensor
  • Internal leak in vacuum brake sensor
  • Cracked or disconnected vacuum hose
  • Defective one-way check valve in the vacuum supply hose
  • Insufficient engine vacuum

How to Check

If the brake pedal requires extra effort to depress and depressing it makes a hissing sound, then that means the brake booster is defective and must be replaced.

Experts recommend a loaded booster (sold with the master cylinder included), as the master cylinder leakage is the chief contributing factor in booster failure.

To further diagnose, you will need a diagnostic scanner, a manual vacuum gauge, a digital volt/ohmmeter, and a reliable source of vehicle information to diagnose a code P050F.

Start the diagnosis with a visual inspection of the vacuum supply hose to the vacuum booster. If the hose is connected and in good working condition, then start the engine. Make sure to secure the vehicle in park or neutral. Remove the one-way check valve carefully, (at the end of the vacuum supply hose) from the booster. Make sure is sufficient vacuum reaching the booster. If you’re not sure, then you can use the manual vacuum pressure gauge to test for sufficient vacuum.

First Step

With KOEO (key on, engine off), unplug the connector from the VBS and then probe for reference voltage at the appropriate pin of the connector using the positive test lead. Use the negative test lead to test for a ground. If reference voltage and a ground are present, proceed to step 2.

Second Step

Set the DVOM at ohms setting and check the VBS. Follow the testing procedure and specifications set by the manufacturer in testing the VBS. If the sensor fails to comply with the specs, then that means it’s defective. If the sensor is in good condition, proceed to the third step.

Third Step

With KOER (key on, engine running) probe signal voltage at the VBS connector using the DVOM’s positive test lead. Then, ground the negative lead to a good battery ground. The signal voltage must reflect the same degree displayed in the MAP sensor on the scanner data display. There will be a vacuum pressure to voltage chart in your vehicle information source. Compare the voltage discovered at the signal circuit to the appropriate entry on the chart. If it doesn’t coincide with the chart, then you may have a defective VBS.

If the voltage is within the specifications, then proceed to the next step.

Fourth Step

Find the PCM and use the DVOM to ensure the VBS signal circuit voltage is there. Then, use the positive test lead of the DVOM to probe the VBS signal circuit. Connect the negative test lead to a good ground. If there is no signal in the VBS connector at the corresponding circuit of the PCM connector, then there might be an open circuit problem between the PCM and the VBS.

If all circuits are good, and the VBS is within the specs, then the problem could be in the PCM or PCM programming.

How to Fix

Depending on your diagnosis, common repairs for this code are:

  • Replacement of brake booster
  • Repair or replacement of damaged vacuum brake sensor
  • Repair or replacement of vacuum leak, cracked or disconnected vacuum hose
  • Repair or replacement of defective one-way vacuum supply hose check valve
  • Replacement or reprogramming of the PCM

Make sure you check the TSB (technical service bulletins) regarding the error code and its symptoms. Many times manufacturers have provided the thorough and comprehensive guide to accurately diagnose and repair problems.

If you have exhausted all other possibilities and you still can’t find the root of the problem, then the PCM may be what is wrong with your vehicle.