DTC B1443 Saturn ION I

The BCM detects that the Off/Run/Crank signal is shorted to B+ for more than 10 seconds in the current ignition cycle.

Action Taken When the DTC Sets

1. The BCM stores the DTC to memory.
2. The BCM operates in a fail-safe power mode dependent on the last valid power mode detected and the state of the engine run flag data on the serial data communications circuits.
3. The other modules on the vehicle operate in a fail-safe power mode dependent on the last valid power mode transmitted by the BCM and the state of the engine run flag on the serial data communications circuits.

Conditions for Clearing the DTC

1. A current DTC clears on the next malfunction free cycle.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

Diagnostic Aids

1. A history DTC maybe caused by an intermittent short or open in the Off/Run/Crank circuit.
2. The BCM supplies a +5-regulated voltage source to the ignition switch to develop the Off/Run/Crank signal.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. 5: This step test for an open circuit in the wiring between the ignition switch and the BCM.
2. 6: This tests the +5-volt regulated supply in the BCM.
3. 7: This tests the ignition switch for a closed circuit between the +5-volt regulated supply and the Off/Run/Crank circuit.
4. 10: This tests the wiring of the Off/Run/Crank circuit for a shot to ground or voltage. This test may be expedited using the DTC to direct the testing. DTC B1442 short to ground or DTC B1443 short to voltage.
5. 11: This tests for an internal short to ground or voltage in the ignition switch. The key must be removed and installed as directed or a false diagnosis will occur.

DTC B1441, B1442, or B1443

Circuit Description

The internal fault detection is handled inside the control module. No external circuits are involved.

DTC Descriptor

This diagnostic procedure supports the following DTC

DTC C0550 Electronic Control Unit (ECU) Performance

Conditions for Running the DTC

The microprocessor runs the program to detect an internal fault when power up is commanded. The only requirements are voltage and ground. This program runs even if the voltage is out of the valid operating range.

Conditions for Setting the DTC

1. The control module detects an internal write malfunction.
2. The control module detects an internal checksum malfunction.

If equipped, the following module specific actions may occur

1. The ABS indicator turns on.
2. The BRAKE Warning indicator turns on.
3. The SERVICE 4WD indicator turns on and the system will be disabled.
4. The Service 4 Wheel Steering indicator turns on and the system will be disabled.
5. The SERVICE RIDE SYS or SERVICE RIDE CONTROL message is displayed.
6. The SERVICE SUSPENSION SYS message is displayed.
7. The traction control system (TCS) indicator turns ON.

1. A current DTC clears when the malfunction is no longer present.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

1. This DTC may be stored as a history DTC without affecting the operation of the module. If stored only as a history DTC and not retrieved as a current DTC, do not replace the module.
2. If this DTC is retrieved as both a current and history DTC, replace the module.

DTC C0550

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for state of health (SOH) monitoring. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. When a module does not associate an identification number with at least one critical parameter within about 5 seconds of beginning serial data communication, DTC U1000 or U1255 is set. If more than one critical parameter does not have an identification number association, the DTC will only be reported once.

DTC Descriptors

This diagnostic procedure supports the following DTCs

1. DTC U1000 Class 2 Data Link Malfunction
2. DTC U1255 Lost Communications

1. Voltage supplied to the module is in the normal operating voltage range of 9-16 volts.
2. Diagnostic trouble codes U1300, U1301, and U1305 do not have a current status.
3. The module operation or the vehicle power mode requires serial data communication to occur.

At least one critical operating parameter has not been associated with an identification number within about 5 seconds after beginning serial data communication.

The module uses a default value for the missing parameter.

1. A current DTC U1000 will clear when all critical operating parameters for the module have been associated with an identification number, or at the end of the current ignition cycle.
2. A history DTC U1000 will clear after 50 ignition switch ON/OFF cycles with no repeat of the failure.

When a malfunction, such as an open fuse to a module occurs while modules are communicating, a Lost Communication DTC for a specific module is set as a current DTC. When the modules stop communicating, the current Lost Communication DTC is cleared, but the history DTC remains. When the modules begin to communicate again, the module with the open fuse will not be learned by the other modules, so DTC U1000 is set current by the other modules. If the malfunction occurs when the modules are not communicating, only DTC U1000 or U1255 is set.

The numbers below refer to the step numbers on the diagnostic table.

1. 1: A Lost Communication with XXX DTC with a history status may indicate the cause of U1000.
2. 2: The module that is not communicating is the likely cause of U1000 or U1255 being set.
3. 5: The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
4. 6: The module which was not communicating may have set Lost Communication with XXX DTCs for those modules that it was monitoring.
5. 7: The module that was not communicating may have set Lost Communication with XXX DTCs for those modules that the module was monitoring.
6. 11: The modules that communicate indicate the module that cannot communicate. You must clear the DTC from the modules in order to avoid future misdiagnosis.
7. 13: If all modules are communicating, the module that set U1000 may have done so due to some other condition.
8. 14: The module that set U1000 is the likely cause of the malfunction.

DTC U1000 and U1255

Modules connected to the class 2 serial data circuit monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. When a module receives a message for a critical operating parameter, the module records the identification number of the module which sent the message for State of Health monitoring, Node Alive messages. A critical operating parameter is one which, when not received, requires that the module use a default value for that parameter. Once an identification number is learned by a module, it will monitor for that modules Node Alive message. Each module on the class 2 serial data circuit which is powered and performing functions that require detection of a communications malfunction is required to send a Node Alive message every 2-5 seconds. When no message is detected from a learned identification number for 5 seconds, a DTC U1xxx, where xxx is equal to the three digit identification number.

The control module ID number list below provides a method for determining which module is not communicating. A module with a class 2 serial data circuit malfunction or which loses power during the current ignition cycle will have a Loss of Communication DTC set by other modules that depend on information from that failed module. The modules that can communicate will set a DTC indicating the module that cannot communicate.

Control Module ID

When more than one Loss of Communication DTC is set in either one module or in several modules, diagnose the DTCs in the following order

1. Current DTCs before history DTCs unless told otherwise in the diagnostic table.
2. The DTC which is reported the most times.
3. From the lowest number DTC to the highest number DTC.

This diagnostic procedure supports the following DTCs

1. DTC U1001 Lost Communications With Powertrain Multiple Control System
2. DTC U1254 Unassigned

1. The vehicle power mode, ignition switch position, requires serial data communication to occur.
2. The module supply voltage is in the normal operating range of 9-16 volts.

A message from a learned identification number has not been detected for the past 5 seconds.

1. A current DTC will clear when a Node Alive message from the failed identification number is detected on the class 2 serial data circuit or at the end of the current ignition cycle.
2. A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

When multiple Loss of Communication DTCs are set concurrently, the likely cause is a bad connection at the fuse block-left instrument panel (I/P) class 2 serial data connector. Refer to Control Module References .

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

1. 7: The module which was not communicating on the class 2 serial data circuit may have set the Loss of Communication DTCs for the modules it was monitoring.

DTC U1001-U1254