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The Heat Exhaust Gas Oxygen (HEGO) Sensor
HEGO voltage output.
The Heated Exhaust Gas Oxygen Sensor
(HEGO) is an emissions control compo-
nent. In the event of a failure, the HEGO
should only be replaced with the recom-
mended OEM replacement part. The
HEGO is sensitive to silicone based prod-
ucts and can become contaminated.
Avoid using silicone sealers or air or fuel
hoses treated with a silicone based lubri-
cant.
TMAP SENSOR
The Air Temperature/Manifold Absolute Pressure
or TMAP sensor is a combination of two sensors:
1) A variable resistor used to monitor the differ-
ence in pressure between the intake manifold
and outside or atmospheric pressure. The
ECM monitors the resistance of the sensor to
determine engine load (the vacuum drops
when the engine is under load or at wide
open throttle) and may alter the fuel mixture
to improve performance and emissions.
2) The Manifold Air Temperature (MAT or IAT)
sensor is a variable resistance thermistor lo-
cated in the air intake passage which
measures the temperature of the incoming air.
The ECM uses the resistance value to monitor
incoming air temperature and calculate the en-
gine’s airflow requirement. The ECM provides
a voltage divider circuit so that when the air is
cool, the signal reads a higher voltage, and
lower when warm. On cold starts, the ECM ri-
chens the fuel/air mixture.
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