ECM
EC-923
< ECU DIAGNOSIS >
[VQ40DE]
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driving pattern), the 1st trip DTC is cleared from the ECM memory. If the same malfunction is detected in the
2nd trip, both the 1st trip DTC and DTC are saved in the ECM memory and the MIL illuminates. In other words,
the DTC is saved in the ECM memory and the MIL illuminates when the same malfunction occurs in two con-
secutive trips. If a 1st trip DTC is saved and a non-diagnostic operation is performed between the 1st and 2nd
trips, only the 1st trip DTC will continue to be saved. For malfunctions that blink or illuminate the MIL during
the 1st trip, the DTC and 1st trip DTC are saved in the ECM memory.
Procedures for clearing the DTC and the 1st trip DTC from the ECM memory are described in "HOW TO
ERASE EMISSION-RELATED DIAGNOSTIC INFORMATION".
For malfunctions in which 1st trip DTCs are displayed, refer to "EMISSION-RELATED DIAGNOSTIC INFOR-
MATION ITEMS". These items are required by legal regulations to continuously monitor the system/compo-
nent. In addition, the items monitored non-continuously are also displayed on CONSULT-III.
1st trip DTC is specified in Service $07 of SAE J1979/ISO 15031-5. 1st trip DTC detection occurs without light-
ing up the MIL and therefore does not warn the driver of a malfunction. However, 1st trip DTC detection will not
prevent the vehicle from being tested, for example during Inspection/Maintenance (I/M) tests.
When a 1st trip DTC is detected, check, print out or write down and erase (1st trip) DTC and Freeze Frame
data as specified in Work Flow procedure Step 2, refer to
EC-462, "Trouble Diagnosis Introduction"
. Then per-
form DTC Confirmation Procedure or Overall Function Check to try to duplicate the malfunction. If the mal-
function is duplicated, the item requires repair.
How to Read DTC and 1st Trip DTC
DTC and 1st trip DTC can be read by the following methods.
With CONSULT-III
With GST
CONSULT-III or GST (Generic Scan Tool) Examples: P0340, P0850, P1148, etc.
These DTCs are prescribed by SAE J2012/ISO 15031-6.
(CONSULT-III also displays the malfunctioning component or system.)
No Tools
The number of blinks of the MIL in the Diagnostic Test Mode II (Self-Diagnostic Results) indicates the DTC.
Example: 0340, 0850, 1148, etc.
These DTCs are controlled by NISSAN.
• 1st trip DTC No. is the same as DTC No.
• Output of a DTC indicates a malfunction. However, GST and the Diagnostic Test Mode II do not indi-
cate whether the malfunction is still occurring or has occurred in the past and has returned to nor-
mal. CONSULT-III can identify malfunction status as shown below. Therefore, using CONSULT-III (if
available) is recommended.
DTC or 1st trip DTC of a malfunction is displayed in SELF-DIAGNOSTIC RESULTS mode of CONSULT-III.
Time data indicates how many times the vehicle was driven after the last detection of a DTC.
If the DTC is being detected currently, the time data will be [0].
If a 1st trip DTC is saved in the ECM, the time data will be [1t].
FREEZE FRAME DATA AND 1ST TRIP FREEZE FRAME DATA
The ECM records the driving conditions such as fuel system status, calculated load value, engine coolant tem-
perature, short term fuel trim, long term fuel trim, engine speed, vehicle speed, absolute throttle position, base
fuel schedule and intake air temperature at the moment a malfunction is detected.
Data which are saved in the ECM memory, along with the 1st trip DTC, are called 1st trip freeze frame data.
The data, saved together with the DTC data, are called freeze frame data and displayed on CONSULT-III or
GST. The 1st trip freeze frame data can only be displayed on the CONSULT-III screen, not on the GST. For
details, see
EC-528, "CONSULT-III Function (ENGINE)"
.
Only one set of freeze frame data (either 1st trip freeze frame data or freeze frame data) can be saved in the
ECM. 1st trip freeze frame data is saved in the ECM memory along with the 1st trip DTC. There is no priority
for 1st trip freeze frame data and it is updated each time a different 1st trip DTC is detected. However, once
freeze frame data (2nd trip detection/MIL on) is saved in the ECM memory, 1st trip freeze frame data is no
longer saved. Remember, only one set of freeze frame data can be saved in the ECM. The ECM has the fol-
lowing priorities to update the data.
Priority
Items
1
Freeze frame data
Misfire — DTC: P0300 - P0306
Fuel Injection System Function — DTC: P0171, P0172, P0174, P0175
2
Except the above items (Includes A/T related items)
3
1st trip freeze frame data