Technical Training
NP10-V8JLR: AJ133 5.0-Liter DFI V8 Engine 04/14/2009
3-15
Engine Management System
Knock Sensors
KNOCK SENSORS
The ECM uses active knock control, which serves to
prevent engine damaging pre-ignition or detonation
under all operating conditions, enabling the engine to
operate without additional safety margins.
The ECM uses 4 piezo-ceramic knock sensors to determine
the point at which a cylinder is pre-detonating. Two sensors
are mounted on the intake side of each cylinder head.
Each sensor monitors engine knock by converting the
engine block noise into a suitable electrical signal, which
is then transmitted back to the ECM via a twisted-pair
cable. The signal is processed within the ECM to iden-
tify the data that characterizes knocking.
This information is compared to known signal profiles to
determine whether pre-ignition is present. If so, the
closed loop control system retards the ignition on that
cylinder for a number of cycles, after which it gradually
moves back towards its original setting.
Safety Precautions CAUTION: Terminals in sensor and connec-
tor are gold plated for corrosion/temperature
resistance. Do not probe connections.
NOTE:
Accurate orientation of the knock sensors on the
cylinder block is required to ensure correct connection to
the vehicle wiring harness.
Failure Modes
• Sensor open circuit
• Short circuit to vehicle ground or battery voltage
• Faulty component or incorrectly torqued / coming loose
• Noise on vehicle 12V supply could look like knock signal causing knock fault
• Min fault usually due to open circuit
• Max fault short circuit to battery voltage or extreme mechanical engine noise/piston slap
• ECM calculates the default value if one sensor fails on each bank of cylinders
Failure Symptoms
• Knock control is disabled and a default ‘safe ignition map’ is used
• Possible rough running and reduced engine perfor- mance
Failure Mode Behaviors
• The vehicle control system constantly checks open circuit of knock sensor. Therefore, the knock sensor
is connected to the power source via pull-up line of
the ECM.
• When short/open circuit occurs to the knock sensor signal circuit, the system detects it, sets failure flag,
and commences maximum retard control on spark
advance.
• As far as the behavior of knock sensor is concerned, however, the above-mentioned failure modes cannot
cause serious outcomes such as heat generation,
smoke emission and/or fire hazard.
NP10V8100
Specification
Function
Power Source N/A
Wiring Type Twisted Pair
Shunt Resistance 4.8M Ohms
Operating Range 3kHz – 22kHz
Mounting Torque 20Nm +/- 3.8Nm
3-2404/14/2009NP10-V8JLR: AJ133 5.0-Liter DFI V8 EngineTechnical Training
Heated Oxygen SensorsEngine Management System
Downstream Heated Oxygen Sensors
The latest switching downstream exhaust sensors are
precise-control heated oxygen sensors (HO2S). These
sensors have a tighter lean/rich tolerance compared to
previous HO2S. The only visible distinction between the
current and previous HO2S is the part number.
The downstream HO2S uses smaller elements in its con-
struction to enable quicker heat-up times to control fuel
metering at lower temperatures (emissions).
The primary function of the downstream HO2S is to
ensure correct operation of the three way catalyst.
The downstream HO2S uses Zirconium technology that
produces an output voltage dependant upon the ratio of
exhaust gas oxygen to the ambient oxygen. The device
contains a Galvanic cell surrounded by gas-permeable
ceramic, the voltage of which depends upon the level of
O2 diffusing through.
Nominal output voltage of the device for lambda = 1 is
300 – 500mV. As the fuel mixture becomes richer (<1)
the voltage tends towards 900mV and as it becomes
leaner (lambda > 1) the voltage tends towards 0 volts. The downstream HO2S are mounted in the exhaust sys-
tem part way in the rear of the catalyst.
Downstream HO2S Output
NP10V8115
V
λ = 1
4.5V
