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Reading Diagnostic Trouble Codes (DTCS)









DIAGNOSTIC DISPLAY

During diagnostic operation, all information will be displayed on the Season and Trip Odometers of the IPC, unless otherwise noted.

Due to the limited display space available, single letter identifiers are often used for each of the major computer system. These identifiers are:
E for ECM, B for BCM, I for IPC, and R for SIR.

TROUBLE CODE DISPLAY
After diagnostics is entered, any trouble codes stored in computer memory will be displayed on the season odometer. Codes may be stored for the ECM, BCM, or SIR systems.

Each trouble code consists of the system abbreviation (E, B, or R), a three digit code, and the letter C or H. All codes for each system are displayed together in the order of their three digit number (lowest first - i.e. EO13, EO14, etc.). The final digit of the code, a C or an H is used to indicate whether the code is current or history. C means the fault was still present the last time the diagnostic test was run, while H means the failure was not present the last time the code was tested for.

If no codes are present for a system, a NO N CODE message (with N being the system abbreviation - E, B, or R) will be displayed. if the communication line to a component is not operating, a NO x DATA message will be displayed, indicating that the ECM could not communicate with that system.

At any time during the display of codes, if the "FAN DOWN" button on the ECCP is depressed, the display of codes will be bypassed.

SELECTING THE SYSTEM
Following the display of trouble codes, the first available system will be displayed (i.e. "EC?," for ECM). While selecting a system to test, any of the following actions may be taken to control the display:
1. Depressing the "OFF" button on the ECCP will stop the system selection process and return the display to the beginning of the trouble code sequence.
2. Depressing the "FAN DOWN" button on the ECCP will display the next available system selection. This allows the display to be stepped through all system choices. This list of systems ("EC?," "BC?," "IPC?," and SIR?) can be repeated following the end of the system list.
3. Depressing the "FAN UP" button on the ECCP will select the displayed system for testing.
4. Depressing the "BI-LEVEL" button on the ECCP will exit diagnostics and return to normal IPC and ECCP operation.

SELECTING THE TEST TYPE
Having selected a system, the first available test type will be displayed (i.e. DATA EC?). While selecting a specific test type, any of the following actions may be taken to control the display:
1. Depressing the "OFF" button on the ECCP will return to the next available system.
2. Depressing the "FAN DOWN" button on the ECCP will display the next available test type for the selected system. This allows the display to be stepped through all available test type choices. This list of test types can be repeated following the display of the last test type.
3. Depressing the "FAN UP" button on the ECCP will select the displayed test type. At this point the first of several specific tests will appear.
4. Depressing the "BI-LEVEL" button will exit diagnostics.

SELECTING THE TEST
Data, Inputs, Outputs, Or Override General
Four characters of the Season Odometer display will contain a test code to identify the selection. The first tw0 characters are letters which identify the system and test type and the last two characters numerically identify the test. The trip odometer will display the selected value as seen by the computer.

While selecting a specific test, any of the following actions may be taken to control the display:
1. Depressing the "OFF" button on the ECCP will stop the test selection process and return the display to the next available test type for the selected system.
2. Depressing the "FAN DOWN" button on the ECCP will display the next smaller test number for the selected test type. If this button is pressed with the lowest test number displayed, the highest test number will then appear.
3. Depressing the "FAN UP" button on the ECCP will display the next larger test number for the selected test type. If this button is pressed with the highest test number displayed, the lowest test number will then appear.

Data - Specific (ECM, BCM)
Selection of the DATA? test type will result in the first available test being displayed. (i.e. XD for E or B DATA). The Trip Odometer will then display the Data value the system computer sees for of the selected test.

Inputs - Specific (ECM, BCM, IPC)
Selection of the INPUT? test type will result in the first available test being displayed. (i.e. XI for E, B, or I INPUTS) The Trip Odometer will then display the voltage level (HI or LO) of the selected input to the system. Additionally, the third digit of the trip odometer will be a 0 or an X. An X indicates that the input has cycled since the test was selected. This indicator may be reset be selecting a new test, and then returning to the present test (i.e. press FAN UP and then FAN DOWN).

Outputs - Specific (ECM, BCM)
Selection of the OUTPUT? test type will result in the first available test being displayed. (i.e. XO for E or B OUTPUTS). The Trip Odometer will then display the voltage level (Hi or LO) of the selected output of the system. This level will then be cycled between HI and LO voltage states every three seconds.

Overrides - Specific (ECM, BCM)
Upon selecting an OVERRIDE test function, current operation of that function will be represented as a percentage of its full range and this value will be displayed on the ECCP. The display will alternate between "--" and the normal program value. This alternating display is a reminder that the function is not currently being overridden.

Pressing the TEMP "UP" and TEMP "DOWN" buttons on the ECCP begins the override at which time the display will no longer alternate to "__." Pressing the TEMP "UP" button increases the value while the TEMP "DOWN" button decreases the value. Normal program control can be resumed in one of three ways:
1. Selection of another override will cancel the current override.
2. Selection of another system (ECM, BCM, IPC, or SIR) will cancel the current override.
3. Overriding the value beyond either extreme (0 or 99) will display "__" momentarily and then jump to the opposite extreme.

If the button is released while "__" is displayed, normal program control will resume and the display will again alternate.

The override test type is unique in that any other test type within the selected system may be active at the same time. After selecting an override test pressing the OFF button will allow selection of another test type, (i.e. DATA, INPUTS, or OUTPUTS). The ECCP panel will continue to display the selected override. By selecting another test type and test, while at the same time pressing the TEMP "UP" of TEMP "DOWN" button, it is possible to monitor the effect of the override on different vehicle parameters.

BCM overrides BS06 and BS07 are special cases which are covered in more detail in the following DIAGNOSTIC PARAMETERS.
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