Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer has noticed a problem with the electricity going to the part that helps the car stop safely. It's like when a toy doesn't work because the batteries are not connected properly.
The ABS (Anti-lock Braking System) pump motor requires a specific voltage to operate correctly. If the voltage supply to the pump motor circuits A and B do not match or correlate as expected, this code is triggered.
The ABS module monitors the supply voltage to the pump motor circuits A and B. If there is a discrepancy between the expected and actual voltage levels in these circuits, it indicates a potential issue with the wiring, connectors, or the pump motor itself. This discrepancy can affect the operation of the ABS system.
• ABS warning light on the dashboard
• ABS system may not function properly
• Unusual noises from the ABS pump
• Faulty ABS pump motor
• Damaged wiring or connectors in the ABS circuit
• Faulty ABS control module
ABS: Anti-lock Braking System
OBD-II: On-Board Diagnostics, second generation
• Inspect the ABS pump motor and related wiring for damage.
• Check the voltage supply to the ABS pump motor circuits A and B.
• Test the ABS control module for faults.
• Repair or replace damaged wiring or connectors.
• Replace the faulty ABS pump motor.
• Replace the ABS control module if necessary.
• Multimeter
• OBD-II scanner
• Basic hand tools
$200 - $800
Moderate
• Chevrolet Silverado
• GMC Sierra
• Cadillac Escalade
• Regularly inspect ABS wiring and connectors.
• Ensure the battery and charging system are in good condition.
• Perform routine ABS system checks.
Electrical Circuit Issue
• Avoid driving aggressively until the issue is resolved.
• Have the vehicle inspected by a professional mechanic.
Repairs may be covered under the vehicle's powertrain or ABS warranty, depending on the age and mileage of the vehicle.
This code has been commonly reported in vehicles with high mileage or those exposed to harsh environmental conditions.
Moderate – While the vehicle can still be driven, the ABS system may not function properly, which can affect braking performance.
Driving with a malfunctioning ABS system can increase the risk of accidents, especially in slippery conditions.
• Vehicle parked on a level surface
• Engine off and ignition in the ON position
The ABS pump motor is typically located near the brake master cylinder in the engine compartment.
Q: Can I drive with the C05A9 code?
A: Yes, but it's not recommended as the ABS system may not function properly, affecting braking performance.
Q: Will this code clear itself?
A: The code may clear itself after the issue is resolved, but it often requires a scan tool to reset.
Pro · Four-system diagnostics
A handheld scanner aimed at engine, transmission, ABS, and airbag diagnostic work.
Chassis and ABS faults usually need a scanner that can read brake-system data directly.
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Useful when reassembly torque matters for wheel, suspension, and under-hood fasteners.
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Universal · Drive-on ramps
Helpful for safer access underneath the vehicle during exhaust, EVAP, and underbody inspection work.
Helpful for safer access during underbody inspection work.
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