Tech Tip: Brake Pedal Sinks When First Pulling Away (2001-'05 Impala and Monte Carlo)
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Tech Tip: Brake Pedal Sinks When First Pulling Away (2001-’05 Impala and Monte Carlo)

Customers may complain of a very slight loss of speed and sinking of the brake pedal when first pulling out of a driveway or parking lot.

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Customers may complain of a very slight lose of speed and sinking of the brake pedal when first pulling out of a driveway or parking lot. The problem will occur at 10 mph and will not occur again until the key is turned off and another drive cycle is started. The ABS light maybe illuminated, but in the majority of cases it will not.

Vehicles: 2001-2005 Chevy Impala and Monte Carlo with DBC-7 ABS Systems

Cause: What the driver is feeling is the ABS System performing a “self check” as part of normal operations. When the ignition is switched on, the warning lamps are all illuminated for a few seconds for a bulb check, then turned off. The solenoids are also commanded on and off, as is the pump motor. The EBCM looks for proper component operation and does a self-check of its own internal circuits. As soon as vehicle speed reaches 10 mph, a dynamic test occurs if the brake pedal is depressed. The driver may notice pedal movement while applying the brake and a slight loss of speed as the system checks itself. The operation of the wheel speed sensors is also monitored continuously while driving.

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The problem may be more noticeable if the friction materials are too aggressive or if the rotors have a layer of corrosion. Also, worn caliper seals and hardware can cause problems during the self check.

If a fault is detected, a code will be stored in the memory, the ABS warning lamp will be illuminated and the ABS system will be deactivated for the remainder of the drive cycle. The red brake warning light may also come on if there is a possibility that the ABS malfunction may affect dynamic rear proportioning.

If the malfunction is no longer present the next time the vehicle is driven, the code will become a history code and the warning lamp will not come back on. Codes will be automatically cleared from memory if no codes are set off during 100 consecutive drive cycles.

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There are NO flash codes available with this system so a scan tool  with ABS software is required to read and clear stored codes. The DBC-7 system also provides “enhanced” data which can be read through the scan tool.

Solution: Make sure the brakes and ABS system are in working order. The check is a normal part of the operation of the vehicle.

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