DTC U0020
| DTC U0020 |
| Diagnostic Instructions |
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Perform the
Diagnostic System Check - Vehicle
prior to using this diagnostic procedure.
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Review
Strategy Based Diagnosis
for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions
provides an overview of each diagnostic category.
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| DTC Descriptor |
DTC U0020 00
Low Speed CAN Communication Bus Performance
| Circuit/System Description |
Modules connected to the GMLAN serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have programmed information about what messages are needed to be exchanged on the serial data circuits. The messages are also supervised and some periodic messages are used by the receiver module as an availability indication of the transmitter module.
DTC U0020 is generated if fewer modules are detected in the bus before the modules can learn the ID numbers of the other modules. If the communication bus is activated, or if the power supply to the modules disappears when the car's electrical system is switched off and then connected, U0020 will be generated in certain modules.
| Conditions for Running the DTCs |
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Voltage at the modules is in the normal operating voltage range.
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The vehicle power mode requires serial data communication to occur.
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The DTC U2100 does not have a current status.
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| Conditions for Setting the DTC |
A supervised periodic message that includes the transmitter module availability has not been received.
| Action Taken When the DTCs Sets |
The module uses a default value for the missing parameter.
| Conditions for Clearing the DTC |
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A current DTC clears when the malfunction is no longer present.
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A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
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| Circuit/System Verification |
Diagnosis of this DTC is accomplished via the symptom or an additional DTC, Refer to Symptoms - Data Communications DTC U0100-U02FF .
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