OBD-II Code P0558: Brake Booster Pressure Sensor Circuit High

What Does P0558 Mean?

P0558 means the Powertrain Control Module (PCM) detects the brake booster pressure sensor voltage signal is stuck high. This sensor measures vacuum pressure inside the brake booster, which multiplies foot force on the brake pedal. When signal voltage stays too high, the computer assumes a critical power brake system fault and triggers the Check Engine Light.

Technical definition: The SAE/OBD-II definition is "Brake Booster Pressure Sensor Circuit High". This DTC sets when the PCM registers a voltage from the brake booster pressure sensor above the manufacturer's specified threshold (typically 4.8V or higher) for a predetermined period (usually 0.2 to 2.0 seconds).

Can I Drive With P0558?

no_not_recommended. Driving is highly dangerous. A P0558 code indicates an imminent failure of the power brake assist system. Without warning, the brake pedal becomes extremely hard to press, dramatically increasing stopping distance. A stop from 60 MPH that normally takes 120 feet requires 400 feet or more. Drive only if absolutely necessary, directly to a repair facility.

Common Causes

• Faulty Wiring Harness or Poor Connector (Very Common) — On 2017-2021 GM models, the wiring harness is the primary culprit. Poor terminal tension or electromagnetic interference (EMI) from ignition components causes a false high voltage signal.
• Failed Brake Booster Pressure Sensor (Common) — The sensor fails internally from age or moisture, defaulting to a continuous high voltage signal (near 5.0 volts) back to the PCM.
• Brake Booster Vacuum Leak (Less Common) — Cracked hoses or a faulty check valve between the engine and brake booster cause incorrect pressure readings.
• Low Power Steering Fluid (Hydroboost Systems) (Less Common) — Vehicles with hydraulic 'hydroboost' systems use power steering fluid pressure instead of engine vacuum. Low fluid levels or a failing pump trigger pressure-related codes, frequently causing misdiagnosis.
• Defective Brake Booster (Rare) — An internal failure, such as a ruptured diaphragm, causes a complete loss of vacuum and triggers the code, usually accompanied by a loud hissing sound.
• Brake Fluid Leak into Booster (Rare) — A leaking master cylinder rear seal allows corrosive brake fluid into the vacuum booster, destroying the diaphragm and sensor.
• Control Module Software Glitch (Rare) — The control module firmware misinterprets the sensor signal, requiring a dealer software update to resolve.
• Faulty Powertrain Control Module (PCM) (Very Rare) — The vehicle's main computer fails to process the sensor signal correctly. Consider this only after exhaustively ruling out all other possibilities.

Symptoms

• Hard Brake Pedal — The brake pedal suddenly becomes very difficult to push, requiring significantly more leg strength to stop the vehicle.
🎬 Watch: How to diagnose a hard brake pedal and booster.
• Increased Stopping Distance — Due to the loss of power assist, the vehicle takes much longer to stop, posing a severe safety risk.
• Warning Lights Illuminated — The Check Engine Light turns on, often accompanied by a 'Service Power Brake Assist' message or a red brake warning light.
• ABS/ESC Disabled — The control module disables the Anti-lock Braking System (ABS) and Electronic Stability Control (ESC) as a precaution.
• Hissing Noise — A hissing sound from the brake booster area indicates a severe vacuum leak.
• Engine Stalls When Braking — Unmetered air from a large vacuum leak disrupts the air-fuel mixture, causing the engine to run rough or stall when braking.

Diagnostic Flowchart

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

Common Fixes & Costs

• Perform GM TSB #20-NA-071 (Harness & Hose Replacement) — Parts: $80-$150, Labor: $150-$300, ~1.3 hr book time (Intermediate)
• Replace Brake Booster Pressure Sensor — Parts: $50-$150, Labor: $75-$150, ~0.8 hr book time (DIY)
• Repair Damaged Wiring or Connector — Parts: $10-$30, Labor: $200-$400, ~2.5 hr book time (Advanced)
• Repair Vacuum Leak (Hose/Valve Replacement) — Parts: $20-$60, Labor: $50-$150, ~0.5 hr book time (DIY)
• Replace Brake Booster — Parts: $150-$400, Labor: $300-$700, ~3.0 hr book time (Professional)

Used vs. New Parts: Buying Guide

When a used part is worth it: Buying used electronic parts like the sensor or wiring pigtail is not recommended. A used brake booster assembly from a low-mileage vehicle is a cost-effective option if the part number matches exactly.

Donor-vehicle mileage cap: roughly under 60000 miles for the part to have meaningful remaining life.

Donor quality checklist:

• Verify the donor vehicle was not scrapped due to brake system or electrical failure.
• Avoid wiring from vehicles in rust-belt states due to corrosion risk.
• Match the part number exactly.

Decision logic:

• If The part is a sensor, wiring harness, or pigtail → Always buy new. The failure mode is electronic wear or corrosion, which is invisible on a used part.
• If The part is a complete brake booster assembly and the vehicle is over 100K miles → A new or professionally remanufactured part is strongly recommended due to the high labor cost of replacement.
• If The GM TSB #20-NA-071 applies → You must buy the specific new harness and hose assembly listed in the bulletin.

Warranty tradeoff: Used parts typically have a 30-90 day warranty, which does not cover labor. New aftermarket parts offer a 1-year to limited lifetime warranty.

Worst-case if a used part fails: $400-$800 if a used booster fails after installation, requiring you to pay labor a second time.

What Happens If You Wait — Timeline

1. 0-1 week: Code P0558 sets. The brake pedal feels intermittently hard, especially on startup, but power assist often returns during driving. (MPG impact: 0%% · Added cost: $0)
2. 1 week - 2 months: Loss of power assist becomes frequent. The driver must occasionally apply massive force to the pedal. A slight rough idle develops if caused by a vacuum leak. (MPG impact: 0-5%% · Added cost: $0-$100 in wasted fuel and high potential for an at-fault accident.)
3. 2-6 months: Power assist is completely gone. Stopping distances are dangerously increased. The driver applies enough force to physically stress the brake pedal assembly or firewall. (MPG impact: 0-10%% · Added cost: $500-$1500 for firewall or pedal assembly damage.)
4. 6+ months: Catastrophic failure. Continued driving with a major vacuum leak causes engine stalling. Operating the vehicle is reckless. (MPG impact: 15%+% · Added cost: $1500-$3000+ to cover secondary mechanical damage and accident-related costs.)

Cost of Not Fixing It

• Immediate: Sudden loss of power brake assist, leading to a hard brake pedal and dramatically increased stopping distance. (Added cost: Potential for an at-fault accident, with costs ranging from thousands to catastrophic.)
• 1-3 months: If caused by a vacuum leak, the engine runs lean, leading to poor performance and setting other engine codes. (Added cost: $200-$500 for diagnosing new, related engine codes.)
• 3+ months: Applying excessive force to a hard pedal damages the brake pedal assembly or firewall. (Added cost: $500-$1500 for mechanical repairs to the pedal assembly or firewall.)

Diagnosis Steps

1. Check for Technical Service Bulletins (TSBs)
   Search for TSBs related to your vehicle's make, model, year, and 'P0558'. Manufacturers, especially GM (TSB #20-NA-071), have issued specific bulletins that lead directly to the known cause and official repair procedure.
   Tools: Internet access (Beginner)
2. Visual Inspection
   Inspect the entire brake booster system. Look for cracked or disconnected vacuum hoses. Examine the sensor's electrical connector for corrosion or damage. If the vehicle has a hydroboost system, check the power steering fluid level.
   Tools: Flashlight (Beginner)
3. Scan Tool Live Data Analysis
   Connect an OBD-II scanner and monitor the 'Brake Booster Pressure Sensor' PID. With the engine running, a reading stuck at or near 5.0 volts that does not change when braking confirms the 'Circuit High' condition.
   Tools: OBD-II Scanner with Live Data (Intermediate)
4. Test the Sensor by Disconnecting It
   With the scan tool monitoring live data, disconnect the sensor's electrical connector. If the high voltage reading drops to 0V, the sensor is internally shorted. If the high voltage reading remains, the fault is a short-to-voltage in the wiring harness.
   Tools: OBD-II Scanner with Live Data (Intermediate)
5. Check for Voltage and Ground at the Connector
   With the key on (engine off) and sensor disconnected, use a multimeter to test the harness terminals. You should find a 5-volt reference wire, a ground wire (near 0V), and a signal wire (near 0V). Significant voltage on the signal wire confirms a short-to-power in the harness.
   Tools: Multimeter (Advanced)
6. Verify Ground Integrity
   Set your multimeter to Ohms (Ω) and measure resistance between the ground pin on the harness connector and the negative battery terminal. A reading over 1.0 ohm indicates a corroded or broken ground wire causing a floating voltage.
   Tools: Multimeter (Advanced)
7. Wiggle Test the Harness
   Keep the scan tool or multimeter connected to the signal wire. Carefully wiggle sections of the wiring harness. If the voltage reading spikes or drops out, you have located an intermittent open or short in the wiring.
   Tools: OBD-II Scanner or Multimeter (Advanced)
8. Check for Vacuum
   Connect a vacuum gauge to the hose feeding the brake booster. At idle, a healthy engine produces 18-21 inches of Hg. A reading below 15 in-Hg points to a vacuum leak or a bad check valve.
   Tools: Vacuum Gauge (Advanced)
9. Perform a Scope Pattern Test
   Connect a lab scope to the sensor's signal and ground wires. A good sensor shows a smooth voltage transition as vacuum changes. A faulty sensor shows glitches, dropouts, or a flat line stuck at 5 volts.
   Tools: Automotive Oscilloscope (Professional)

When This Code Triggers (Freeze-Frame Conditions)

• Engine Coolant Temp: 175-210°F (The code typically sets when the engine is at full operating temperature.)
• RPM: 650-800 RPM (Triggers at idle or just after startup when the PCM performs initial system checks.)
• Engine Load: 15-30% (Detected under low-load conditions, such as idling in gear, where stable vacuum is expected.)
• Vehicle Speed: 0 mph (Freeze frame data frequently shows the vehicle stationary when the fault logs.)

Related Codes

• P0557 — The direct opposite code for 'Brake Booster Pressure Sensor Circuit Low'. On GM vehicles, the same wiring fault causes voltage to fluctuate and trigger either code.
• P0556 — 'Brake Booster Pressure Sensor Circuit Range/Performance'. Sets when the sensor's signal is erratic or intermittent, often pointing to a failing sensor.
• C0299 — A Chassis code for 'Brake Booster Pressure Sensor Performance'. Often stored in the ABS module alongside a P0558 in the PCM.
• P0555 — 'Brake Booster Pressure Sensor Circuit'. A general fault code indicating a malfunction in the circuit but not a specific 'high' or 'low' condition.

Climate & Environmental Factors

• Humidity and Moisture: High humidity accelerates corrosion on the sensor's electrical connector pins, increasing resistance and causing the voltage signal to be misinterpreted as high.
• Extreme Cold: In very cold weather, plastic vacuum hoses and rubber seals become brittle and prone to cracking, leading to vacuum leaks.
• High Altitude: At higher altitudes, ambient atmospheric pressure is lower. A marginal sensor or small vacuum leak becomes more apparent and triggers a fault code.

How to Talk to a Mechanic About This Code

Say this: "I have a P0558 code and a hard brake pedal. If it's a GM vehicle, please check TSB 20-NA-071 first. For any make, please start by checking the brake booster pressure sensor's live data voltage to see if it's stuck high. Confirm if the issue is the sensor, wiring, or a vacuum leak before replacing parts."

Signals you are informed about common causes and want a specific diagnostic approach. It directs the mechanic to test rather than just replace parts, preventing unnecessary costs.

Avoid saying:

• 'My check engine light is on.'
• 'My brakes feel weird.'
• 'Just fix it.'

Questions to ask before authorizing the repair:

• What was the sensor's voltage reading on the scan tool?
• Did you test the circuit by disconnecting the sensor to see if the voltage dropped?
• If recommending a new brake booster, did you confirm a vacuum leak or internal diaphragm failure?
• For a GM vehicle, are you performing the TSB fix that includes the new harness?
• What is the warranty on the parts and labor?

Where to Take It: Dealer vs Independent vs Chain

• Dealer: Highly Recommended for affected GM models, as they are most familiar with the specific TSB repair.
  Best for: GM vehicles (2017-2021) with the known TSB #20-NA-071., Vehicles still under warranty., Complex electrical issues requiring a software update.
  Downsides: Highest labor rates., May replace an entire assembly when a smaller component is the cause. (Typical cost: +50% vs. baseline)
• Independent Shop: Best overall fit for most non-GM vehicles. A good independent shop easily diagnoses a sensor vs. wiring fault.
  Best for: Out-of-warranty vehicles where the cause is likely a sensor, hose, or wiring., Owners looking for a balance of expertise and cost.
  Downsides: Quality varies greatly; ensure the shop has ASE-certified technicians., May be less aware of very recent TSBs. (Typical cost: +0% vs. baseline)
• Chain Shop: Use with caution. Acceptable for a simple vacuum hose leak. AVOID for primary diagnosis, especially for electrical issues or the GM TSB.
  Best for: Simple, confirmed vacuum hose replacements.
  Downsides: Technician skill varies dramatically., High pressure to upsell common brake services unrelated to the P0558 code., Less likely to perform in-depth electrical diagnostics. (Typical cost: -10% vs. baseline)

When to Walk Away From the Repair

If the estimated repair cost exceeds 40-50% of the car's private-party value, seriously consider selling or trading it in instead of repairing it.

• Car worth $15000, fix is $700: Fix it. The repair cost is a small fraction of the car's value.
• Car worth $4000, fix is $1100: Borderline. Get a second opinion before proceeding, especially if the diagnosis requires replacing the entire brake booster.
• Car worth $2500, fix is $1500: Walk away. The repair cost is over 50% of the car's value, making it a poor investment.

What Scan Tool You Need for This Code

Minimum: A scanner that can read and graph live data for the Brake Booster Pressure Sensor PID.

A basic $20 code reader only shows the 'P0558' code. It cannot show live voltage data, which is essential to determine if the sensor signal is actually stuck high.

Budget: BlueDriver Pro Scan Tool (~$100) — Connects to your smartphone via Bluetooth and displays/graphs the live voltage from the brake booster pressure sensor.

Mid-range: Foxwell NT510 Elite / Innova 5610 (~$150) — Handheld units that provide detailed live data and access ABS/Brake Control Module data directly.

Professional: Autel MaxiCOM MK808 / XTool D7 (~$450-600) — Offers full-system diagnostics, extensive live data graphing, and bi-directional controls to diagnose complex wiring issues.

Rent vs buy: AutoZone's Loan-A-Tool program allows you to borrow an OBD-II scanner for free. If you only need to diagnose this single issue, renting is the most cost-effective option.

How to Clear the Code After You Fix It

1. Use a professional OBD-II scan tool to erase the DTCs.
2. Reconnect any disconnected components, including the battery.
3. Perform the specific drive cycle recommended by the manufacturer to run readiness monitors.

Drive cycle (~20 minutes): A general drive cycle includes: a cold start, 3 minutes of idling, 10 minutes of mixed city driving, followed by 5 minutes of steady highway driving (55-60 mph).

Readiness monitors affected: Comprehensive Component Monitor (CCM), Evaporative System Monitor, Oxygen (O2) Sensor Monitor

Before emissions retest: drive at least 50 miles to fully set monitors.

Watch out for:

• Disconnecting the battery clears the code but erases all readiness monitors, causing an immediate emissions test failure.
• If the underlying fault is not repaired, the code returns immediately on the next drive cycle.

Will This Fail Emissions / State Inspection?

Yes — this code typically fails an OBD-II emissions inspection.

• California: An illuminated Check Engine Light results in an automatic failure. All readiness monitors must be set to 'Ready' before passing.
• New York: A P0558 code causes an automatic failure of the NYS vehicle inspection.
• Texas: In the 17 counties requiring emissions testing, an active P0558 code causes the vehicle to fail the OBD-II portion of the inspection.

Most Commonly Affected Vehicles

• Cadillac XT5 (2017-2021) — Addressed by GM TSB #20-NA-071. The cause is wiring-related (EMI/poor terminal tension). The fix requires replacing the vacuum hose and installing a new external wiring harness.
• GMC Acadia (2017-2021) — Shares the same platform and wiring issue as the XT5. Covered by TSB #20-NA-071 and TSB #21-NA-045.
• Buick Enclave (2018-2021) — Affected by the issue in GM TSB #20-NA-071. Original wiring is routed too close to ignition coils, causing electrical interference.
• Chevrolet Blazer, Traverse (2018-2021) — Falls under GM TSBs #20-NA-071 and #21-NA-045. The official repair involves abandoning the old sensor wiring and installing a new external jumper harness.
• Ford F-150, Fusion, Edge (2015-2020) — Frequently attributed to a failed sensor due to heat and vibration, or a wiring issue, rather than a single widespread TSB.
• Jeep/Chrysler/Dodge Wrangler, Grand Cherokee, Town & Country (2011-2020) — The cause is often a failed sensor, which is frequently integrated into the vacuum hose assembly, requiring the entire part to be replaced.
• Hyundai Elantra, Sonata (2011-2019) — Typically points towards a faulty sensor or a problem in the electrical circuit. The trigger condition is often a sensor voltage > 4.8V for 0.2 seconds.
• Subaru Outback, Forester, Crosstrek (2015-2022) — CRITICAL: On some models, P0558 indicates a malfunction in the GPS communication circuit or a 'Generator Circuit Low' fault. Verifying the fault's origin with a Subaru-specific scan tool is essential.

Manufacturer-Specific Notes

• General Motors (GM): For 2017-2021 SUVs, TSBs #20-NA-071 and #21-NA-045 are critical. The root cause is a wiring design flaw. The only correct fix is installing a new vacuum hose assembly AND a new wiring harness jumper.
• General Motors (GM): Special Coverage Adjustment N182202780 extends warranty coverage to 10 years/150,000 miles for engine-mounted vacuum pump failures on 2014-2018 trucks, which causes similar hard pedal symptoms.
• Subaru: P0558 refers to a malfunction in the GPS communication circuit or an alternator circuit fault on certain models. A manufacturer-specific scan tool is required to confirm the true source.
• Chrysler/Dodge/Jeep: The brake booster pressure sensor is often permanently integrated into the main brake booster vacuum hose. If the sensor fails, the entire hose assembly must be replaced.
• Mitsubishi: Service manuals provide specific trigger conditions, such as setting P0558 if the ECM detects a sensor output voltage of 4.8V or more for a continuous duration of at least 2 seconds.

Real Owner Stories

2018 GMC Acadia at 75,000 miles

Check Engine Light and 'Service Power Brake Assist' message appeared intermittently. The brake pedal occasionally became very hard to press on startup.

Outcome: A GM dealership identified the issue as TSB #20-NA-071. They installed the updated vacuum hose/sensor assembly and the separate jumper wiring harness (P/N 84773558) for $550. The code never returned.

Lesson: For 2017-2021 GM SUVs, replacing only the sensor wastes money. The updated bypass harness is required to fix the root cause.

2015 Ford F-150 at 110,000 miles

The Check Engine Light came on with code P0558, but the brake pedal felt completely normal.

Outcome: This confirmed an internal sensor short. They replaced the sensor (Ford P/N FL3Z-2C444-A) for $90. The problem was solved.

Lesson: A simple disconnect voltage test confirms whether the sensor itself has shorted internally, preventing unnecessary parts replacement.

2012 Jeep Grand Cherokee at 130,000 miles

A loud hissing sound emerged from the driver's footwell when braking, accompanied by a hard pedal and P0558.

Outcome: A mechanic confirmed the internal booster diaphragm ruptured. The entire brake booster required replacement, costing $900.

Lesson: A loud hissing noise from inside the cabin when braking is a classic sign of a failed brake booster diaphragm, requiring full assembly replacement.

How to Prevent This Code From Triggering

• Apply Dielectric Grease to Connectors (Anytime a connector is disconnected for service) — Seals out moisture and oxygen, preventing pin corrosion that increases resistance and causes false high voltage signals.
• Inspect Brake Booster Vacuum Hoses (Every oil change or annually) — Catches cracks, brittleness, or soft spots before they become large leaks that affect brake performance.
• Secure Wiring Harnesses Away from Heat (During any under-hood maintenance) — Prevents chafing and heat damage, which are common causes of shorts and open circuits.
• Change Brake Fluid per Manufacturer Schedule (Typically every 2-3 years) — Prevents moisture contamination that corrodes the master cylinder rear seal, stopping fluid from leaking into and destroying the booster.

Frequently Asked Questions

What is a brake booster and what does it do?

A brake booster is a round canister located between your brake pedal and the master cylinder. It uses engine vacuum or hydraulic pressure to multiply the force you apply to the brake pedal, making it significantly easier to stop your car.

Is it safe to drive with a P0558 code?

No, it is highly dangerous. The power assist for your brakes could fail at any moment, requiring a sudden and massive increase in pedal force to stop the vehicle. The vehicle should be repaired immediately.

Where is the brake booster pressure sensor located?

The sensor is located in the engine bay on the driver's side. It is typically mounted directly on the brake booster or integrated into the large vacuum hose running from the intake manifold to the booster.

What are the most common misdiagnosis mistakes for P0558?

The biggest mistake is replacing the sensor on a GM vehicle without checking TSB #20-NA-071, as the problem is usually the wiring. Another error is failing to check power steering fluid on a 'hydroboost' system.

Can I just replace the sensor to fix the problem?

Sometimes, but it is not a guaranteed fix. The code is frequently caused by a wiring issue, not the sensor itself. On many GM vehicles, replacing only the sensor will not solve the problem.

How much does it cost to fix a P0558 code?

A diagnostic check typically costs $150. A simple vacuum hose fix is $100-$200, while the common GM TSB repair costs $230-$450. If the entire brake booster needs replacement, the cost exceeds $1,000.

Can I test the brake booster pressure sensor myself?

A DIYer can perform basic checks like visual inspections and using a scan tool to watch live data. Advanced tests, like checking for 5V reference and ground with a multimeter, are also possible. Tracing a short in a complex harness is best left to professionals.

Will clearing the code make the problem go away?

No. Clearing the code only turns off the check engine light temporarily. Because P0558 is caused by a persistent electrical or mechanical fault, the computer detects the issue again very quickly.

Key Takeaways

• P0558 is a critical safety code indicating imminent power brake assist failure, which can increase a 60 MPH stopping distance from 120 feet to over 400 feet.
• For 2017-2021 GM SUVs, TSB #20-NA-071 dictates replacing the vacuum hose and installing a bypass wiring harness; replacing the sensor alone will not fix the $230-$450 repair.
• Diagnose the fault by checking live scan tool data for a voltage stuck above 4.8V, then disconnect the sensor to see if voltage drops to 0V to confirm a shorted sensor.
• On non-GM vehicles, the most frequent cause is an internally shorted brake booster pressure sensor, which costs $125 to $300 to replace.
• Subaru owners must use an OEM-level scanner before replacing brake parts, as P0558 often falsely triggers due to a GPS radio or alternator circuit fault.