Technical TrainingNP10-V8JLR: AJ133 5.0-Liter DFI V8 Engine04/14/20093-23
Engine Management SystemHeated Oxygen Sensors
Upstream Universal Heated Exhaust Gas Oxygen Sensors
In order to improve the control of the air : fuel ratio
(AFR) under varying engine conditions, a linear or ‘uni-
versal’ heated exhaust gas oxygen (UHEGO) sensor is
used in the upstream location. The UHEGO has a vary-
ing current response to changes in the exhaust gas oxy-
gen content.
The AFR can be maintained more precisely within a
range from approximately 12:1 to 18:1, not just stoichio-
metric. Voltage is maintained at approximately 450 mV
by applying a current.
The current required to maintain the constant voltage is
directly proportional to the AFR. A higher current indi-
cates a leaner condition; a lower current indicates a
richer condition. The current varies with the temperature
of the sensor and is therefore difficult to measure for
technician diagnostic purposes.
The upstream UHEGO sensors need to operate at high
temperatures – 750°C (1,382°F) – in order to function
correctly. To achieve this, the sensors are fitted with
heater elements that are controlled by a PWM signal
from the ECM.
The heater elements are operated immediately following
engine start and also during low load conditions when
the temperature of the exhaust gases is insufficient to
maintain the required sensor temperatures.A non-functioning heater delays the sensor’s readiness
for closed loop control and influences emissions. The
PWM duty cycle is carefully controlled to reduce ther-
mal shock risk to cold sensors.
The upstream UHEGO sensors are mounted to the
engine on the exhaust manifolds, in the mating flange to
the exhaust pipes. There is one sensor per bank. The sen-
sors are fitted during engine assembly.
Upstream UHEGO Output
NP10V8108
+10 mA
NOMINAL APPLIED CURRENT
-10 mA
AFR 12:1
APPLIED CURRENT(APPROXIMATE)
AFR 18:1λ = 1
