GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The hydraulic brake Diagnostic System Check is an organized approach to identifying problems associated with the hydraulic brake system. This must be the starting point for any hydraulic brake related concern and will direct you to the next logical step in diagnosing a malfunction.

Test Description

The number below refers to the step number on the diagnostic table.

  1. Lack of communication may be due to a malfunction of the class 2 serial data circuit. The specified procedure determines the particular condition.

  2. The presence of DTCs that begin with "U" indicates that some other module is not communicating. The specified procedure compiles all of the available information before tests are performed.

Step

Action

Yes

No

1

Install a scan tool.

Does the scan tool power up?

Go to Step 2

Go to Scan Tool Does Not Power Up in Data Link Communications

2

  1. Turn ON the ignition.
  2. Attempt to establish communication with the following control modules.
  3. • Powertrain
    • Hydraulic 4WAL 4 Sensor
    • Instrument Panel Cluster

Does the scan tool communicate with the control modules listed above?

Go to Step 3

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

3

Select the Display DTCs function on the scan tool for the following control modules.

    • Powertrain
    • Hydraulic 4WAL 4 Sensor
    • Instrument Panel Cluster

Does the scan tool display any DTCs?

Go to Step 4

Go to Symptoms - Hydraulic Brakes

4

Does the scan tool display any DTCs that begin with a "U"?

Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications

Go to Step 5

5

Does the scan tool display DTC P0562, P0563, P0621, P0622, P1637 or P1638?

Go to Diagnostic Trouble Code (DTC) List in Engine Electrical

Go to Diagnostic Trouble Code (DTC) List