OBD-II trouble code
C0900: Control Module Power Circuit Malfunction
The ABS module (EBCM) detected a supply-voltage problem — most often voltage too high — on its power circuit and shut its functions down to protect itself. ABS and traction/stability control are disabled, but base braking still works.
Quick facts
- System
- Chassis
- Category
- ABS / Traction Control
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $800
- DIY difficulty
- Intermediate DIY
What does C0900 mean?
The electronic brake control module (EBCM) monitors the voltage on its power supply circuit and will disable itself if that voltage moves outside a safe window. C0900 is typically a high-voltage (overvoltage) fault: when system voltage climbs too high — on many GM vehicles the threshold is roughly above 16 volts for a fraction of a second — the module shuts down its outputs to avoid electrical damage. It's essentially a self-protection code, and it points at the vehicle's charging and power distribution rather than at a mechanical brake part.
Because the module has powered down its brake-control functions, anti-lock braking, traction control, and stability control are disabled and their warning lights come on. Your ordinary hydraulic brakes still work — the pedal stops the car normally — but the electronic assistance stays off until the voltage problem is corrected and the code cleared. This code is closely related to the module's other supply-voltage codes, so it should be read as a symptom of the electrical system, not as a reason to replace the EBCM.
The usual culprits are charging-system problems: an overcharging alternator or failing voltage regulator driving the voltage too high, or high-resistance battery cables, corroded terminals, and poor grounds that let voltage swing. On some platforms manufacturers have issued service information tying this code to specific high-current fuse or battery-cable connections that corrode or arc. Diagnose by watching system voltage and inspecting the battery, cables, grounds, and alternator output before condemning any module. Definitions and exact thresholds vary by manufacturer, so confirm the specifics in service data for your vehicle.
Common causes
- Overcharging alternator or failed voltage regulator driving system voltage too high
- Corroded, loose, or high-resistance battery cables and terminals
- Poor or corroded ground causing voltage swings
- Weak or failing battery
- Corroded/arcing high-current fuse or power connection at the module feed
- Faulty EBCM (rare — confirm the electrical system first)
Symptoms
- ABS warning light on
- Traction control and stability control warning lights on
- ABS, traction, and stability features disabled
- Possible other voltage-related warnings if the charging system is overcharging
- Normal (base) braking still works
Diagnostic steps
- 1.Scan all modules and record C0900 with any companion voltage codes (C0899, C0800) or system-wide voltage codes in other modules.
- 2.Measure battery voltage with the engine running and check charging-system output — an overcharging alternator (typically reading well above ~15V) is a prime suspect for an overvoltage code.
- 3.Inspect the battery terminals, cables, and high-current connections for corrosion, looseness, or heat/arcing damage.
- 4.Perform voltage-drop tests on the module's power feed and ground.
- 5.Load-test the battery and confirm it and the charging system are healthy.
- 6.Repair the charging/power fault, clear the code, and retest; only consider the module if the electrical supply is confirmed good and the code still returns.
Repair cost
$100 – $800
The fix depends on the electrical cause. A battery replacement runs roughly $120-$300, and an alternator (the common cause of overvoltage) commonly $300-$700 installed. Cleaning or repairing corroded cables, terminals, or grounds can be a low-cost repair. Replacing the EBCM is rarely necessary for this code — the module is protecting itself from a supply-voltage problem, so fix the electrical system first.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with battery replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.