P0556 on 2016-2017 Jeep Grand Cherokee: Brake Booster Pressure Sensor Causes and Fixes

What's Unique About the 2016-2017 Jeep GRAND CHEROKEE

On the 2016-2017 Jeep Grand Cherokee (WK2 generation) and its platform-mate the Dodge Durango, the P0556 code is specifically called out in manufacturer Technical Service Bulletins (TSBs) as being potentially caused by a software logic issue. These TSBs indicate the code may appear alongside other DTCs and that the primary recommended fix is to reprogram the Powertrain Control Module (PCM) with updated software. This makes it critical to check the vehicle's software calibration status before replacing any hardware, as a simple reflash at a dealership may resolve the fault.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on.
• Brake pedal is hard to press.
• Increased effort required to stop the vehicle.
• Brake system warning light may be illuminated.
• Possible hissing noise from the brake booster area, indicating a vacuum leak.
• Spongy or inconsistent brake pedal feel.

Most Likely Causes

1. PCM Software Requires Update 🔴 High Probability FCA issued TSBs #18-049-20 and #18-024-17 REV. C specifically to address this code being set erroneously due to overly sensitive PCM logic.
   How to confirm: A Jeep dealership or a qualified shop with a wiTECH scan tool can check the current PCM software calibration number against the latest version specified in the TSBs.
   Typical fix: Reprogram (reflash) the Powertrain Control Module (PCM) with the latest software. This is a dealer or specialty shop procedure.
   Est. part cost: $0
2. Faulty Brake Booster Pressure Sensor 🟡 Medium Probability → Shop Power Brake Booster Sensors can fail over time due to internal electronic faults, contamination, or heat cycles.
   How to confirm: After confirming the PCM software is up-to-date, test the sensor's voltage output with a multimeter or view its live data on a scan tool. 🎬 Watch: Understanding the P0556 sensor circuit and range The voltage should change in response to vacuum changes, typically between 0.5V and 4.5V.
   Typical fix: Replace the brake booster pressure sensor.
   Est. part cost: $50-$150
3. Vacuum Leak 🟡 Medium Probability Rubber vacuum hoses, including the check valve integrated into the main vacuum line, can crack, split, or become disconnected over time due to heat and age.
   How to confirm: Visually inspect all vacuum hoses connected to the brake booster for cracks, brittleness, or loose connections. A smoke test is the most effective way to find hard-to-see leaks in the booster itself or the lines.
   Typical fix: Repair or replace the leaking vacuum hose or check valve assembly.
   Est. part cost: $10-$50
4. Wiring or Connector Issue ⚪ Low Probability The wiring harness to the sensor can become damaged from engine vibration, heat, or corrosion at the connector pins.
   How to confirm: Visually inspect the sensor's connector and wiring for any signs of damage, corrosion, or loose pins. Perform a continuity test on the wiring if a visual inspection is inconclusive.
   Typical fix: Repair the damaged wiring or clean/replace the connector.
   Est. part cost: $5-$100

Rare But Worth Checking

• Failing Brake Booster: → Shop Power Brake Booster An internal diaphragm leak in the brake booster itself can cause a loss of vacuum, triggering the P0556 code. This is less common than a sensor or hose failure. A smoke test can confirm a leak from the booster housing. Replacement can be costly, with estimates for a 2016-2017 Grand Cherokee ranging from $682 to $825.
• Powertrain Control Module (PCM) Fault: In very rare cases where a software update does not fix the issue and all other components test good, the PCM may have an internal hardware failure.

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs). The first step for this specific vehicle is to determine if TSB #18-049-20 or #18-024-17 REV. C applies. If the PCM software has not been updated, this is the most likely cause and should be addressed before any parts are replaced.
2. Scan the PCM for P0556 and any other stored codes. Note the associated codes mentioned in the TSBs (P06EF, P040B, U1424, P2681, P2299) as their presence strongly suggests the software update is needed.
3. Perform a thorough visual inspection of the brake booster, the pressure sensor, its connector, and all associated vacuum lines. Look for obvious cracks, damage, loose connections, or signs of corrosion.
4. With the engine running, listen for any hissing sounds near the brake booster that would indicate a vacuum leak.
5. Using a scan tool with live data capabilities, monitor the brake booster pressure sensor reading. The reading should be stable at idle and change predictably as you apply and release the brake pedal. Compare this to manufacturer specifications.
6. If the sensor readings are erratic or do not respond, and the software is confirmed to be up-to-date, test the sensor's wiring. Check for 5V reference, ground, and signal continuity back to the PCM.
7. If the sensor and wiring test good, perform a smoke test. Introduce smoke into the vacuum port on the brake booster to definitively check for leaks in the booster diaphragm, the check valve, or the vacuum lines.
8. If all components and wiring test good and the PCM software is current, the brake booster pressure sensor itself is the most likely failed component.

Parts You'll Likely Need

• Brake Booster Pressure Sensor — This is the most frequent hardware failure for a P0556 code, as the sensor itself can fail electronically. This should only be replaced after confirming the PCM software is up-to-date.
  Trusted brands: Mopar, Standard Motor Products (p/n BST157), Wells (p/n 5S17531), Carquest Premium (p/n WSA4066)
  OEM price range: $100-$180
  Aftermarket price range: $50-$120
• Brake Booster Vacuum Hose — Cracked or leaking vacuum hoses are a common cause of incorrect pressure readings, leading to this code. The check valve is often integrated into this hose assembly.
  Trusted brands: Mopar, Gates
  OEM price range: $30-$70
  Aftermarket price range: $15-$40

Related Codes That Often Appear With This One

• P06EF — Mentioned in TSB #18-049-20, relates to Engine Restart Performance, suggesting a link to the vehicle's stop-start system which relies on proper vacuum.
• P040B — Listed in both TSB #18-049-20 and #18-024-17 REV. C, this EGR Temperature Sensor code may appear as part of a broader software-related issue.
• U1424 — Also listed in the same TSBs, this is a network code indicating 'Implausible Engine Torque Signal Received', pointing towards a potential communication or software logic issue between modules that can be resolved by the same PCM update.
• P2681 — Listed in TSB #18-024-17 REV. C, this code for the Engine Coolant Bypass Valve can also be falsely triggered by the same software issue.
• P2299 — Listed in TSB #18-024-17 REV. C, 'Brake Pedal Position/Accelerator Pedal Position Incompatible' is another code that points to a software logic fault.

Technical Service Bulletins (TSBs) & Recalls

• 18-049-20: Supersedes the earlier TSB. Involves reprogramming the PCM for P0556 and other codes (P06EF, P040B, U1424, etc.) on 2016-2017 Grand Cherokee and Durango models.
• 18-024-17 REV. C: Also calls for a PCM reflash to address P0556 and a list of other falsely set DTCs on vehicles built on or before March 06, 2017.

Platform-Specific Known Issues

• Jeep issued Technical Service Bulletins #18-049-20 and #18-024-17 REV. C, which are critical for diagnosing P0556. They state that this code, often with others like P06EF, P040B, and U1424, can be caused by a software logic issue. The official fix is a PCM reflash, which should be the first step in diagnosis before replacing any parts.

Mechanic-Grade Diagnostic Values

• Brake Booster Pressure Sensor Signal Voltage — expected: Typically 0.5V (no boost/high vacuum) to 4.5V (full boost/low vacuum). Voltage should increase proportionally as the brake pedal is pressed.. Failure: Voltage is flat, spikes erratically, or is outside the expected range when pedal pressure is applied.
• Engine Vacuum at Idle — expected: 18 to 22 inches of Mercury (inHg).. Failure: Significantly lower vacuum can indicate a leak in the booster, a hose, or the check valve, which would cause the sensor to read incorrectly.

Scan Tool Commands That Help

• wiTECH (or equivalent professional scanner): PCM Reprogram/Flash — This is the primary repair procedure specified by TSBs #18-049-20 and #18-024-17 REV. C for a P0556 code on this vehicle, especially if other related codes are present. It should be performed before hardware replacement.

Wiring & Ground Locations

• Brake Booster Pressure Sensor Connector — On or near the brake booster, which is mounted to the driver's side firewall in the engine compartment.. This is the direct connection point for the sensor. Corrosion, damage, or loose pins at this 3-terminal oval connector can cause the P0556 code. Replacement pigtails often use 18-gauge wire, indicating the circuit's requirements.

Real Owner Repair Stories

• Jeep Wrangler Forums (Jeep Wrangler (JL) with 3.6L eTorque) — Rock solid brake pedal with no 'give' when attempting to start the engine after it had been sitting. Required extremely hard pedal pressure to start.
  ❌ Tried (didn't work) Multiple start attempts with normal pedal pressure.
  ✅ What actually fixed it The issue was diagnosed as vacuum leaking down in the brake booster over time, likely due to a faulty check valve in the vacuum supply hose. While the engine started with excessive pedal force, the underlying cause points to a slow vacuum leak rather than a sensor failure. This can be tested by turning the engine off and seeing if the pedal gets stiff after only one or two pumps, or if it rises on its own while being held down.

Model Year Variations Within This Range

• 2016-2017 (specifically before March 06, 2017): According to TSB #18-024-17 REV. C, vehicles built on or before March 06, 2017, are particularly susceptible to the software logic issue that can falsely trigger the P0556 code. Vehicles built after this date may have the updated software from the factory, making a hardware fault (like the sensor or a vacuum leak) a more likely cause.