it would look at the anto lock brakes real closely. the chevy trcks are very well know for low speed abs activation. which is usually a wheel speed sensor sending a irractic reading, causing the abs to activate when it shouldnt. and if the problems only occurs at times may very well be a abs problem. here is a service bulletin on this matter please read and see what you think
This bulletin is being revised to update the correction and warranty information. Please discard Corporate Bulletin Number 02-05-25-006A (Section 05 -- Brakes).
Some customers may comment on ABS activation at low speeds, usually below 8 km/h (5 mph). Upon investigation, the technician will find no DTCs set.
The cause of this condition may be an increased air gap between the wheel speed sensor and the hub reluctor ring due to rust and debris built up on the sensor mounting surface.
Measure AC voltage and clean wheel speed sensor mounting surfaces.
(Canadian P/N 89022218)
(Package of 2 cans)
Rust Penetrating Lubricant
(Each can will service 50+ vehicles)
(Canadian P/N 993037)
(Package of 12 tubs)
Wheel Bearing Lubrication - Tub
(Each tub will service 25+ vehicles
These tests will not find all master cylinder malfunctions. If you cannot find the cause with these tests, refer to Hydraulic Brake Diagnostic System Check .
This procedure inspects for the following conditions:
This procedure tests for the following conditions:
DEFINITION: Excessive Brake Pedal Travel
Was the Hydraulic Brake Diagnostic System Check performed?
Go to Step 2
Go to Hydraulic Brake Diagnostic System Check
Inspect the disc brake pads and brake shoe linings for the following:
Refer to Brake Pad Inspection in Disc Brake or Brake Shoe Inspection in Drum Brakes.
Do any of the above conditions apply?
Go to Step 3
Go to Step 4
Replace the brake linings. Refer to Brake Pads Replacement in Disc Brakes or Brake Lining Replacement in Drum Brakes.
Is the repair complete?
Go to Step 22
Inspect the brake rotors for the following:
Refer to Brake Rotor Lateral Runout Check in Disc Brakes
Go to Step 5
Go to Step 6
Resurface the brake rotor. Refer to Brake Rotor Refinishing in Disc Brakes.
If refinishing the brake rotor results in a thickness that is less than the thinnest (Refinishing) thickness, replace the rotor. Refer to Brake Rotor Replacement in Disc Brakes.
Go to Component Specifications in Disc Brakes
Inspect the drum brakes for improper adjustment. Refer to Drum Brake Adjustment in Drum Brakes.
Are the brakes improperly adjusted?
Go to Step 7
Go to Step 8
Adjust the drum brakes properly. Refer to Drum Brake Adjustment in Drum Brakes.
Inspect the axle seals for leakage.
Is there any seal leakage?
Go to Step 9
Go to Step 10
Replace the axle oil seals.
Inspect the brake assembly for missing or loose attachments. Refer to Brake Caliper Inspection in Disc Brakes or Brake Drum Inspection in Drum Brakes.
Are there any missing or loose attachments?
Go to Step 11
Go to Step 12
Replace or tighten the attachments as necessary.
Inspect the wheel cylinders and calipers for leakage.
Are any of the components leaking?
Go to Step 13
Go to Step 14
Replace the leaking components. Refer to Brake Caliper Replacement in Disc Brakes or Wheel Cylinder Replacement in Drum Brakes.
Inspect the hydraulic brake system for leaks. Refer to Brake Hose and Pipe Diagnosis .
Is there any sign of leakage?
Go to Step 15
Go to Step 16
Tighten the brake hose or pipe fittings. Refer to Fastener Tightening Specifications .
Inspect the master cylinder for leakage. Refer to Master Cylinder Diagnosis .
Is the master cylinder leaking?
Go to Step 17
Go to Step 18
Overhaul the master cylinder. Refer to Master Cylinder Overhaul .
Inspect the brake system for air. Refer to Hydraulic Brake System Bleeding .
Is there air in the system?
Go to Step 19
Bleed the brake system. Refer to Hydraulic Brake System Bleeding .
Inspect the brake fluid for contamination. Refer to Brake Fluid and Brake Fluid Handling .
Is the brake fluid contaminated?
Go to Step 21
Flush the hydraulic brake system. Refer to Hydraulic Brake System Flushing .
Verify the proper brake system operation.
Does the original condition still exist?
Go to Step 1
here is the functional test for hydro boost.
The hydraulic booster uses fluid pressure from the power steering system. A malfunctioning power steering system can affect the hydraulic booster. A malfunctioning booster can affect the steering system. Before beginning extensive testing, perform the following procedure.
Notice: Power steering fluid and brake fluid cannot be mixed. If brake seals contact power steering fluid or steering seals contact brake fluid, seal damage will result.
The pedal should fall away, and then push back against your foot.
review this information and runs some of the basic test to verify what is working like it is supposed too. then maybe pull abs fuse out and roadtest and see if problems reoccurs. anything you dont understand please ask me to explain