Circuit Description

Proper operation of the vehicle stability enhancement system (VSES) is highly dependent on the ability to apply brake pressure to a selected wheel, through the brake pressure modulator valve (BPMV), as commanded by the electronic brake control module (EBCM). The EBCM may not be able to detect certain mechanical failures that may cause the VSES to perform poorly. This diagnostic procedure is designed to help diagnose concerns of poor vehicle stability, that may occur without the presence of any DTCs, by verifying the following.

The tires are the correct size, properly inflated and in acceptable condition.
There are no mechanical problems in the steering system.
There are no mechanical problems in the suspension system.
There are no mechanical problems in the base brake system.
All of the VSES related hydraulic controls within the BPMV are functioning correctly.

Vehicle Stability Enhancement System Poor Performance

Step	Action	Yes	No
1	Did you review the system Description and Operation and perform the necessary inspections?	Go to Step 2	Go to Symptoms - Antilock Brake System
2	Inspect all four tires for the following. Improper size Incorrect air pressure Uneven tread wear Insufficient tread Did you find and correct a concern?	Go to Step 11	Go to Step 3
3	Inspect the vehicle for following. Worn, loose or binding steering linkage components. Refer to Steering Linkage Inspection (Steering Linkage Inspection) or Steering Linkage Inspection (Idler Arm Inspection) in Steering Linkage. Proper power steering operation. Refer to Power Steering System Description and Operation (w/o Electro-Hydraulic Steering) in Power Steering System. Did you find and correct a concern?	Go to Step 11	Go to Step 4
4	Diagnose any suspension symptoms exhibited by the vehicle. Refer to Symptoms - Suspension General Diagnosis in Suspension General Diagnosis. Did you find and correct a concern?	Go to Step 11	Go to Step 5
5	Raise the vehicle so that all four wheels are about 15 cm (6 in) off of the floor. Refer to Lifting and Jacking the Vehicle in General Information. With help from an assistant, verify that the brake at each wheel is applying and releasing properly when the brake pedal is applied and released. Did you find and correct a concern?	Go to Step 11	Go to Step 6
6	Diagnose any hydraulic brake symptoms exhibited by the vehicle. Refer to Symptoms - Hydraulic Brakes in Hydraulic brakes. Did you find and correct a concern?	Go to Step 11	Go to Step 7
7	Install a scan tool. Perform the wheel isolation test procedure on all of the isolation valves. Refer to Brake Pressure Modulator Valve Hydraulic Testing . Did any of the wheel isolation tests fail?	Go to Step 9	Go to Step 8
8	Perform brake pressure application testing. Refer to Brake Pressure Modulator Valve Hydraulic Testing . Did either of the TC isolation valve tests fail?	Go to Step 9	System OK
9	Replace the BPMV. Refer to Brake Pressure Modulator Valve (BPMV) Replacement (w/ JL4) or Brake Pressure Modulator Valve (BPMV) Replacement (w/o JL4) . Did you complete the replacement?	Go to Step 10	-
10	Use the scan tool to perform all of the available BPMV hydraulic tests. Refer to Brake Pressure Modulator Valve Hydraulic Testing . Do the hydraulic tests show the system to be functioning normally?	Go to Step 11	Go to Step 5
11	Test drive the vehicle to verify that the stability concern has been corrected. Has the concern been corrected?	System OK	Go to Step 2