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AJ-V8/5HP24
63
Engine Management
To counteract the increase in engine coolant
temperature that occurs after the engine stops,
at ignition off:
if the fans are already on, the ECM keeps
them on for 5 minutes, or until the ECT
decreases to a pre-determined value,
whichever occurs first
if the fans are off, the ECM determines, from
ECT and intake air temperature inputs, if the
fans need to be switched on. If they do, it
switches them on for 5 minutes, or until the
ECT decreases to a pre-determined value,
whichever occurs first.
Radiator Fan Switching Points
Mode Coolant Temperature, ˚C (˚F) A/C System Pressure, Bar (psi)
On Off On Off
Slow 90 (194) 86 (187) 12 (174) 8 (116)
Fast 97.5 (207.5) 93.5 (200.5) 22 (319) 17.5 (254)
Diagnostics
The ECM performs self test routines and
monitors engine functions, inputs and outputs to
ensure correct operation of the engine and the
engine management system. Hard wired inputs
and outputs are monitored for short and open
circuits, and sensor inputs are also monitored for
range.
Additional checks are run on the more critical
sensor inputs to ensure their validity. Some of the
more critical inputs have substitute or default
values which the ECM adopts if the input is
diagnosed as faulty.
Any faults detected are logged in the ECM
memory as DTC. The ECM also outputs engine
malfunction messages on the CAN and adopts a
default mode of operation. Most default modes
retain some degree of engine operation (limp
home).
The ECM also stores OBD II related DTC
detected by other control modules on the CAN.
Non-OBD II related DTC are retained in the
memory of the control module that detects the
fault.
To prevent false DTC being logged, the
monitoring of some inputs and engine functions
is inhibited while the vehicle is above a given
altitude:
at altitudes of 2438m (8000ft) and
above,the ECM inhibits diagnostics on:
EGR valve and EGR flow; EVAP valve and
EVAP purge flow; idle speed control; misfire
detection; catalytic converter efficiency.
at altitudes of 2652m (8700ft) and
above, the ECM also inhibits diagnostics on:
HO2S; MAFS; O2S.
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