
sensor failure accompanies an Engine Coolant Temperature (ECT) sensor failure, cooling
fan operation may also be affected.
Some manufacturers incorporate the Intake Air Temperature (IAT) sensor as part of the
Mass Air Flow (MAF) sensor (Air Flow Meter).
Knock Sensor
The purpose of the Knock Sensor (KS) is to monitor pre-ignition or "engine knock" and
send the signal to the PCM. The PCM responds by adjusting ignition timing until the
knocking stops. The sensor works by generating a signal produced by the frequency of the
knock as recorded by the piezoelectric ceramic disc inside the KS. The disc absorbs the
shock waves from the knock vibration and exerts a pressure on the metal diaphragm
inside the KS. This compresses the crystals inside the disc which generates a voltage
signal proportional to the frequency of the knock vibration.
MAF Sensor
Mass Airflow (MAF) sensors measure the weight and rate of air moving through a passage
of a known volume or size. Typically, MAF sensors utilize hot wire or thick film technology.
Signals generated may be analog or digital depending on manufacturer. As more air
passes through the MAF sensor, the voltage or frequency increases proportionally. The
PCM uses this information to calculate injector pulse-width and spark advance.
Performance issues from MAF sensor failures range from no-start conditions to stalling,
hesitation, stumble and improper air/fuel mixtures. The MAF sensor values vary from 0.2V
(0 gm/sec) to 4.8V (175 gm/sec).
Some manufacturers incorporate the Intake Air Temperature (IAT) sensor as part of the
Mass Air Flow (MAF) sensor (Air Flow Meter).
Some manufacturers incorporate a 6.0V to 9.0V circuit from the MAF sensor to the PCM to
control the MAF sensor reset signal.
TP Sensor
The Throttle Position (TP) sensor and accelerator pedal position (APP) sensor are the only
sensors sending data to the Powertrain Control Module (PCM) that the vehicle operator
has direct control over. The TP sensor is a three wire potentiometer that provides an
analog signal to the computer. This signal represents how far the throttle plates have
opened.
The Powertrain Control Module calculates how much air should have entered the engine
and compares this value with the Manifold Absolute Pressure (MAP) sensor or Mass Air
Flow (MAF) sensor value. The PCM uses this information to calculate fuel delivery and
ignition timing requirements.
The PCM on vehicles equipped with an electronic transmission utilize the TP sensor in
combination with the MAP and MAF sensor values to determine shift schedules and torque
converter clutch application.
Summary of Contents for TrailBlazer
Page 1: ......
Page 26: ...Fig 3 Typical body and undervehicle maintenance locations Refer to chart for descriptions ...
Page 29: ......
Page 30: ......
Page 31: ......
Page 175: ...Spring free length check Valve spring squareness check ...
Page 192: ...Front of piston mark ...
Page 361: ...5 3L Engine Except Saab Underhood Fuse Block 2003 2005 Early Production ...
Page 469: ...Removing the outer band from the CV boot Removing the inner band from the CV boot ...
Page 470: ...Removing the CV boot from the joint housing Clean the CV joint housing prior to removing boot ...
Page 471: ...Removing the CV joint housing assembly Removing the CV joint ...
Page 472: ...Inspecting the CV joint housing Removing the CV joint outer snap ring ...
Page 473: ...Checking the CV joint snap ring for wear CV joint snap ring typical ...
Page 474: ...Removing the CV joint assembly Removing the CV joint inner snap ring ...
Page 475: ...Installing the CV joint assembly typical ...
Page 553: ...9 Torque the lug nuts to specification 10 Lower the vehicle ...
Page 556: ...Toe in Frame Misalignment Frame misalignment ...
Page 588: ...Bleeding caliper ...
Page 624: ...Manifold gauge set components Refrigerant recovery recycling station ...
Page 676: ...A C Specifications ...
Page 677: ......