When testing, only use a high-impedance (10 mega ohms) digital multi-meter to avoid shorting / shocking the PCM out. On models that are fitted with a Theftlock audio system, verify that the lock out feature is switched off before removing the battery terminal. The self-diagnosis system can only be activated by the TECH 1 SCAN tool-if that is not available, obtain the vehicle codes from a dealer or an authorized repair center. Thermistors that are resistors with varying resistance according to the temperature ought to be high when the temperature is low, and low as the temperature increases. To verify, turn on the multi-meter by selecting the ohms range, remove the harness connector and then place the test probe of the multi-meter on both terminals of the sensor. After checking resistance, check for reference voltage from computer it should be 5.0 volts with ignition switch on. Electrical rotary devices such as the throttle position signal should be tested by back probing the harness connector and noting voltage changes when the signal arm is varied. Intake manifold pressure/vacuum sensor monitors the pressure variation at the intake manifold and should display voltage from below 2.0V when the engine is idle to above 4.0V WOT. Magnetic reluctance sensors including crankshaft and vehicles speed sensors include observing fluctuation of voltage by using AC volt meter when the engine is cranking or by rotating the sensor. Hall effect sensors output ON/OFF signals to the powertrain control module, and should display voltages when the engine is turned over. Dual Hall effect sensors work in the same manner, but they give two different ON/OFF signals. Oxygen sensors measure exhaust gas oxygen content with a voltage signal range of 0.1-0.9 Volts: test for millivolt signals as the engine warms. MAF sensor, records the air getting into the engine and its readout is in grams per second by use of a SCAN tool. Engine vibration is sensed by
Knock Sensors and they generate ac output voltage which should vary when tapped. The NVLD switch lights up when the transaxle is in Park/Neutral taping various systems. The PCM acts on the acoustic knock sensors to alter engine load and the air conditioning compressor clutch for the same as well as the power steering pressure sensor to observe fluid pressure that may cause idle problems. The fuel tank pressure sensor is used during emissions checking of the pressure while the Torque Converter Clutch system in automatic transaxles operates to lock the torque converter at cruising speed while allowing minor adjustments to fuel saving; it requires tools that are special to check and repair.