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Severity: Moderate Code type: Manufacturer-specific (Chevrolet)

Chevrolet P25A2 Code: Brake System Control Module Requested MIL

The brake module stored a fault and asked the engine computer to turn on the check engine light.

Safety first · Consult a professional

  • Braking system affected: ABS may be disabled. Drive carefully and have it checked promptly.

At a glance

Severity: 3/5 – Moderate3/5

Severity: Moderate

Meaning
Brake System Control Module Requested MIL
System
ECU & Outputs · Powertrain
Safe to drive?
With caution
Typical repair cost
$0–$3,000
DIY difficulty
Hard

P25A2 is set by the engine computer when the brake system control module sends a request to light the check engine light. It shows up most on Chevrolet models with GM's electric brake boost system (eBoost), where the brake module also creates the power assist without engine vacuum: the 2019-and-newer Silverado 1500 and Sierra 1500, the Tahoe and Suburban from the 2021 model year, and cars like the Blazer. P25A2 itself says nothing about what's wrong; the real code, such as a brake pressure, pedal, booster or wheel speed sensor fault, is stored in the brake module. A frequent trigger on these trucks is brake pad work: pushing the caliper pistons back with the battery connected can make the module think the hydraulic system has a problem.

Can I keep driving? Check that the pedal feels firm and the truck stops normally before driving. If you see a brake assist or brake system warning, have a hard pedal or reduced power assist, drive only at low speed to a shop or have it towed.

How to read P25A2

How to read P25A2P12253A24
  1. P Powertrain
  2. 2 Generic (SAE)
  3. 5 Speed, idle & inputs
  4. A2 Specific fault

Symptoms

  • Check engine light on together with ABS, traction or brake warnings
  • SERVICE BRAKE ASSIST or brake system warning message
  • Brake pedal harder or lower than usual
  • Appeared right after a brake pad or caliper job
  • Traction control, StabiliTrak or cruise control disabled
  • Generic reader shows only P25A2, no C-codes

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Caliper pistons pushed back during pad replacement with the battery connected, leaving a false pressure fault 30%
  2. Wheel speed sensor or harness fault reported by the brake module 20%
  3. Low brake fluid, air in the system or a real hydraulic leak 15%
  4. Low battery or charging voltage upsetting the electric brake booster 13%
  5. Brake pedal position sensor fault or calibration lost 12%
  6. Brake module software or internal fault 10%

Diagnosis step by step

Diagnostic flow: P25A21Read the brake module codes2Check fluid level and look for leaks3Reset after brake work the GM way4Check system voltage5Test wheel speed sensors ifindicated6Calibrate or update as needed

  1. Read the brake module codes

    Use a scan tool with GM ABS/brake coverage. The brake module codes and their symptom bytes, not P25A2, decide what to check; note them before clearing anything.

    Tools: OBD-II scanner

  2. Check fluid level and look for leaks

    Verify the fluid is between MIN and MAX and look for wet calipers, hoses and lines at each wheel. A real leak or low fluid must be fixed and the system bled before any codes are cleared.

    Tools: Flashlight

  3. Reset after brake work the GM way

    If the code followed a pad job, disconnect the battery negative cable, then press the brake pedal to about two-thirds of its travel, wait around 15 seconds and repeat until the pedal is firm and the pads are seated. Reconnect the battery and clear the codes; if the brake module code returns, continue diagnosis.

    Tools: Screwdriver, OBD-II scanner

  4. Check system voltage

    The electric brake booster draws heavy current, so confirm the battery rests near 12.6 V and charging voltage is normal. Low voltage can set booster and pressure faults that clear once the battery is healthy.

    Tools: Multimeter

  5. Test wheel speed sensors if indicated

    If a wheel speed code is stored, compare all four wheel speeds on a slow drive in live data and inspect that sensor's harness for rubbing or damage from road debris.

    Tools: OBD-II scanner, Flashlight

  6. Calibrate or update as needed

    Pedal position sensor calibration, brake bleed routines and brake module software updates are done with a GM-capable tool. A shop with that tool is the right place if the code persists after the basic checks.

    Tools: OBD-II scanner

Where the parts are

Charging system and control modules – P25A21234567
Charging system and control modules
  1. 1Battery
  2. 2Alternator
  3. 3Engine computer (ECM)
  4. 4CAN bus
  5. 5Transmission
  6. 6Wheel speed sensor
  7. 7High-voltage battery

Repair options & costs

RepairDIY?Estimated cost
Seat pads, reset procedure and clear codes Yes $0–$150
Repair leak and bleed brakes with scan tool No $150–$450
Replace wheel speed sensor Yes $120–$350
Pedal sensor calibration or brake module software update No $100–$300
Replace brake system control module / booster assembly No $1,200–$3,000

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Emissions / smog test impact

Will fail

Because P25A2 turns on the check engine light, the vehicle fails a US OBD emissions test until the brake module fault is repaired and the light is off. States with a safety inspection may also fail it for brake or ABS warnings.

Frequently asked questions

Why does a brake problem turn on the check engine light?

GM programs the brake module to request the check engine light for certain faults, and the engine computer records that request as P25A2. The engine itself is usually fine; the fix is in the brake system.

I just replaced my pads and now have P25A2. What happened?

On trucks with electric brake boost, pushing the caliper pistons back with the battery connected can make the brake module see an unexpected pressure change. Following the battery-disconnect and pedal-seating reset usually clears it if there's no real leak.

Can I clear P25A2 with a basic code reader?

You can erase the engine code, but the brake module code that caused it stays stored and will turn the light back on. You need a tool that can clear codes in the brake module.

How should I do brakes on these trucks to avoid it?

Disconnect the battery negative cable before compressing caliper pistons, work carefully, and afterward pump the pedal until it's firm before reconnecting. Some scan tools also offer a brake service function for this system.

Sources