Scan Tool Testing and Procedures

When using the TECH 1 for ABS system diagnosis, the ABS system is disabled when in communication with the TECH 1. The Anti-Lock indicator lamp will be lit, indicating only power assisted braking is possible. A Bosch ABS adapter is required when connecting the TECH 1 to the ALDL connector.
When performing diagnosis refer to SCHEMATIC DIAGRAMS for wiring circuits, and DIAGNOSTIC CHARTS for SYMPTOM CHARTS A and B.

TECH 1 TEST MODES
Mode FO: Data List
In this mode, TECH 1 continuously monitors wheel speed data and brake switch status. When monitoring speed data, the TECH 1 screen displays signals being sent from wheel speed sensors to the EBCM. In this mode, vehicle can be driven while TECH 1 displays speed data. These reading can be compared with actual vehicle speed to check proper operation. Speed signals can also can be compared with each other to determine whether they are within specification.
If one speed signal differs greatly from another signal, improper operation of that sensor may be indicated. Intermittent speed signals can be located in the DATA LIST mode by checking for signals that vary for no reason.
In DATA LIST mode, the TECH 1 screen displays brake switch operation. When brake pedal is depressed, screen reads ON; when pedal is released, screen reads OFF.

Mode F1: Code History
In this mode, trouble code history is displayed. This data include how many ignition cycles since the trouble code first occurred, brake switch status, vehicle speed and ABS state when fault occurred. Up to three codes are included in the ABS history data.

Mode F2: Trouble Codes
In this mode, the TECH 1 displays trouble codes stored in the EBCM. The EBCM can store up to three different trouble codes. The TECH 1 can also clear codes when in this mode.
When this mode is accessed, trouble codes are displayed, with a three second interval between each code displayed. When each code is displayed, it will be accompanied by a brief description of what that code represents.
After displaying trouble codes, the TECH 1 can be ordered to clear any trouble codes stored in the EBCM. The TECH 1 will respond to a clear codes command by displaying either an "ABS CODES CLEARED" or CODES CLEAR FAIL" on the screen.
The EBCM stores other information about trouble codes which may prove useful in diagnosis procedure. This function is called "ENHANCED DIAGNOSTIC DATA:
a. Brake Switch Status, indicates whether brake light switch was ON or OFF when code was set.
b. ABS State, indicates whether or not anti-lock mode was engaged when code was set.
c. Vehicle Speed, indicates vehicle speed when code was set.
d. Ignition Cycles, indicates how many ignition cycles have occurred since code was set.

Mode F3: ABS Snapshot
The ABS snapshot will help to isolate problems caused by the speed sensor signals which may cause intermittent operation of the ABS system. The ABS SNAPSHOT mode captures data before and after a trigger condition.
If "MANUAL TRIGGER" is selected, the pressed before storing speed sensor information. When TECH 1 is waiting for "ENTER" or "F9" to be pressed, a "W" will be displayed in the lower righthand corner of the display. While the TECH 1 is waiting for the trigger, it continuously stores ABS speed sensor data. The TECH 1 can store up to 81 samples after the trigger. If more than 81 samples occur before the trigger, the oldest data will be discarded. It takes approximately eight seconds for the TECH 1 to store 81 samples.
As soon as "ENTER" or "F9" is pressed, the TECH 1 will begin to store speed sensor data, this is indicated by an "I" displayed on the screen. When data storage is full, the data point when the "ENTER" button was pressed will be displayed indicated by ")" on the display.
To view the speed information that was stored, use the UP ARROW and DOWN ARROW keys. The numbers on the display indicate the sample number relative to the trigger. An "+1" on the display indicates the first sample after the "ENTER" button was pressed. An "-1" on the display indicates the sample proceeding the time when "ENTER" was pressed. By selecting the up and down arrow keys, all of the stored data can be displayed and examined for conditions which might indicate a problem. While displaying data, select F7 to convert English to Metric or select "ENTER" to convert number in the righthand lower corner of the screen to time in seconds.
If "AUTOMATIC TRIGGER" is selected, the TECH 1 will store data which may deviate from normal operating conditions but may not set a code. For example, when driving over bumpy roads or railroad tracks, the wheel speed signal may change rapidly or drop out. This condition may be caused by loose connections or intermittent wiring problems. Using the "AUTOMATIC TRIGGER," data will be stored when the TECH 1 recognizes that a wheel speed signal has deviated from it normal operating range. While the TECH 1 is waiting for a trigger, the "ENTER" or "F9" button may be used to force a trigger. While displaying the information, the cause of the trigger can be displayed by selecting F3.

Mode F4: ABS Tests
This mode performs functional tests on the ABS system which help verify proper system operation. Error conditions can be further identified by testing and observing test results. In the "ABS TESTS" mode the following test can be performed:
a. Solenoid Valve-Pressure Reduction: This test indicates whether specific solenoid valves in the hydraulic modulator release pressure to assigned hydraulic wheel circuits.
b. Solenoid Valve-hold Pressure: This test indicates whether specific solenoid valves in the hydraulic modulator hold pressure in assigned hydraulic wheel circuits.
c. AUTO Test: This test cycles each solenoid valve and operates the pump motor briefly. The EBCM will store an error code if test conditions fail.
The "PRESSURE REDUCE" test activates a selected hydraulic wheel circuit valve, placing it in the pressure reduce position. Valve action can then be verified by checking the appropriate wheel for proper brake action. The TECH 1 will indicate whether the valve action was commanded properly. This test used in conjunction with the "PRESSURE HOLD" test, completely checks each solenoid valve. With the aid of an assistant, perform the following procedure.
1. Have assistant press brake pedal.
2. Set TECH 1 to command "PRESSURE REDUCE" mode.
3. Try to spin wheel being tested, wheel should spin due to reduce command.
The "PRESSURE HOLD" test activates a selected hydraulic wheel circuit valve, placing it in the pressure hold position. Valve action can then be verified by checking the appropriate wheel for proper brake action. The TECH 1 will indicate whether the valve action was commanded properly. This test used in conjunction with the "PRESSURE REDUCE" test, completely checks each solenoid valve. With the aid of an assistant, perform the following procedure.
1. Spin wheel freely, then set TECH 1 to command "PRESSURE HOLD."
2. Have assistant press brake pedal
3. Try to spin wheel being tested, wheel should spin due to hold command, even though brake is applied.