wire is heated to specific temperature differential above incoming air. Two wires inside the MAF Sensors are exposed
to a portion of the airflow entering the engine :
The ambient temperature wire or "cold wire" isn't heated so this wire is the temperature of the surrounding air and
serves as the reference temperature.
The hot wire is heated by the MAF to be a certain amount above the ambient air. As soon as air flows over the wire,
bothwires are cooled. The control circuits then apply more voltage to keep the hot wire at the original temperature
differential. This creates a voltage signal monitored by the ECM. The greater the air flow and wire cooling, the greater
the signal.
• Engine coolant temperature sensor
The Engine Coolant Temperature (ECT) Sensor provides an input voltage to the ECM relating to coolant temperature.
The ECM uses this input signal along with inputs from other sensors to determine injector pulse width and ignition
timing. As coolant temperature varies the ECT Sensor's resistance changes. The change in resistance results in a
different input voltage to the ECM. When the engine is cold, the ECM will operate in Open Loop cycle. It will demand
slightly richer air/fuel mixtures and higher idle speeds until normal temperatures are reached.
• Throttle position sensor
The Throttle Position (TP) Sensor is a variable resistor that provides the ECM with an input signal (voltage) that
represents throttle blade position. The sensor is connected to the throttle blade position. The sensor is connected to
the throttle blade shaft. As the position of the throttle blade changes, the resistance of the TP Sensor changes. The
ECM supplies a 5V reference voltage to the TP Sensor. The TP Sensor output voltage (input signal to the ECM)
represents the throttle blade position. This will usually vary from around 0.25V at minimum throttle opening, the
around 4.7V at wide open throttle.
• Crankshaft position sensor
The Crankshaft Position (CKP) Sensor is used to signal the ECM when a spark and/or fuel injection event required.
The output from this sensor, in conjunction with the Camshaft Position Sensor signal, is used to determine whether
spark or fuel is required in a particular cylinder. The engine will not start without a CKP Sensor signal to the ECM.
Refer to section EE-IG for more information.
• Camshaft position sensor
The Camshaft Position (CMP) Sensor works with the CKP Sensor to provide inputs to the ECM to establish and
maintain correct injector firing order. Refer to section EE-IG for more information.
• Knock sensor
The Knock Sensor is a feedback signal used to control of ignition timing. When knocking occurs, the Knock Sensor
sends the signal to the ECM. The ECM then retards the ignition timing to reduce or eliminate the knock.
• Intake air temperature sensor
This sensor measures the temperature of the intake air and converts its charge into a resistance through a thermister
similar to the ECT Sensor. By monitoring the IAT Sensor, the ECM detects the intake air temperature and use it as
one of the signals to control fuel injectors and ignition timing.
• HO2 (Oxygen) Sensor
Two heated O2 Sensors are used in the vehicle. The sensors produce voltages from 0 to 1 volt, depending upon the
oxygen content of the exhaust has in the exhaust manifold. When a large amount of oxygen is present (caused by a
lean air/fuel mixture), the sensors produce a low voltage. When there is a lesser amount (rich air/fuel mixture) the
sensors produce ahigher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensors
act as a rich-leanswitch.
Both HO2 Sensors are equipped with a heating element that keeps the sensors at proper operating temperature
during all modes of operation. Maintaining correct sensor temperature at all times allows the system to enter into
closed loop operation faster and allows the system to remain in closed loop during periods of extended idle.
• Front HO2 Sensor
The front (upstream) HO2 Sensor is located in the exhaust downpipe after the TWC and provides an input voltage to
the ECM. The input tells the ECM the oxygen content of the exhaust gas. The ECM uses this information to fine tune
the air/fuel ratio by adjusting injector pulse width.
• Rear HO2 sensor
The rear (downstream) HO2 Sensor is located near the outlet end of the catalytic convertor. The rear HO2 Sensor
input isused to detect catalytic convertor deterioration. As the convertor deteriorates, the input from the downstream
sensor begins to match the upstream sensor input except for a slight time delay.
By comparing the rear HO2 Sensor input to the input from the front sensor, the ECM catalytic convertor efficiency.
Symptom Diagnosis charts
Description : Further describes the symptom. Confirm that the chart addresses the actual symptom before beginning
troubleshooting.
Troubleshooting Hints : This describes the possible point of malfunction.