General Specification Electrical Function gmw3110 General Motors Local Area Network Enhanced Diagnostic Test Mode Specification

8.18.1.2 Retrieving the List Of DTCs That Match A Tester Defined Status Mask. 
The tester can retrieve a 
list of DTC numbers and DTCFailureTypes which satisfy a tester defined status mask by sending a request 
with the sub-parameter byte set to readStatusOfDTCByStatusMask ($81). Nodes shall be able to mask on 
more than one bit of the status byte field at a time via a logical 
OR-ing
operation, making it possible for the 
tester to request a node to transmit all DTCs that are 
current 
OR 
history
OR , etc., with a single request. If a 
tester specifies a status mask that contains bits that the node does not support, then the node shall process 
the DTC information using only the bits that it does support. In response to the tester
’s request, the ECU shall 
return a UUDT message to the tester for each DTC and DTCFailureTypeByte combination that satisfies the 
masking criteria specified by the tester (refer to diagram below for response timing). The UUDT response 
message(s) shall contain the 2-byte DTC number, the one byte DTCFailureTypeByte, and the one byte 
DTCStatusByte. Once all DTCs satisfying the tester-specified masking criteria have been transmitted, the ECU 
shall transmit a special endOfDTCReport UUDT message to flag the end of the transmission. Refer to the 
corresponding response message definition table below for formatting details regarding the endOfDTCReport 
message. If no DTC/DTCFailureTypeByte combinations match the masking criteria, then the ECU shall only 
transmit the endOfDTCReport message in response to the tester
’s request. 
The ECU diagnostic application shall transmit the first UUDT response (or USDT-SF negative response) within 
P2
C
of receiving the tester request. Once the first UUDT response has been sent, each subsequent UUDT 
response message(s) shall be transmitted within P2
C
from the previously transmitted ($81) UUDT response 
message. 
Note:
The P2
C
timing is the maximum interval that an ECU should send the UUDT responses. It is acceptable 
to send them at a rate faster than P2
C
. 
If the ECU diagnostic application determines that the tester request message is acceptable, but cannot 
transmit the first UUDT response message within the P2
C
time window, it shall transmit a $7F $A9 $78 
RequestCorrectlyReceived-ResponsePending to the tester to invoke enhanced timing P2
C
*. Once the ECU is 
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