Engine Electrical Devices: Overview Suzuki Reno I

Engine Coolant Temperature Sensor Description

The Engine Coolant Temperature (ECT) sensor is a thermistor (a resistor which changes value based on temperature) mounted in the engine coolant stream. Low coolant temperature produces a high resistance (100,000 ohms at -40 °C [-40 °F]) while high temperature causes low resistance (70 ohms at 130 °C [266 °F]). The Engine Control Module (ECM) supplies 5 V to the ECT sensor through a resistor in the ECM and measures the change in voltage. The voltage will be high when the engine is cold, and low when the engine is hot. By measuring the change in voltage, the ECM can determine the coolant temperature. The engine coolant temperature affects most of the systems that the ECM controls. A failure in the ECT sensor circuit should set a diagnostic trouble code P0117 or P0118. Remember, these diagnostic trouble codes indicate a failure in the ECT sensor circuit, so proper use of the chart will lead either to repairing a wiring problem or to replacing the sensor to repair a problem properly.

Throttle Position Sensor Description

The Throttle Position (TP) sensor is a potentiometer connected to the throttle shaft of the throttle body. The TP sensor electrical circuit consists of a 5 V supply line and a ground line, both provided by the Engine Control Module (ECM). The ECM calculates the throttle position by monitoring the voltage on this signal line. The TP sensor output changes as the accelerator pedal is moved, changing the throttle valve angle. At a closed throttle position, the output of the TP sensor is low, about 0.5 V. As the throttle valve opens, the output increases so that, at Wide Open Throttle (WOT), the output voltage will be about 5 V.

The ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent bursts of fuel from the injector and an unstable idle, because the ECM thinks the throttle is moving. A problem in any of the TP sensor circuits should set a Diagnostic Trouble Code (DTC) P0121 or P0122. Once the DTC is set, the ECM will substitute a default value for the TP sensor and some vehicle performance will return. A DTC P0121 will cause a high idle speed.

Intake Air Temperature Sensor Description

The Intake Air Temperature (IAT) sensor is a thermistor, a resistor which changes value based on the temperature of the air entering the engine. Low temperature produces a high resistance (4,500 ohms at -40 °C [- 40 °F]), while high temperature causes a low resistance (70 ohms at 130 °C [266 °F]).

The Engine Control Module (ECM) provides 5 V to the IAT sensor through a resistor in the ECM and measures the change in voltage to determine the IAT. The voltage will be high when the manifold air is cold and low when the air is hot. The ECM knows the intake IAT by measuring the voltage.

The IAT sensor is also used to control spark timing when the manifold air is cold.

A failure in the IAT sensor circuit sets a diagnostic trouble code P0112 or P0113.

Throttle Actuator Control (TAC) System Description

The Throttle Actuator Control (TAC) system is used to improve emissions, fuel economy and driveability. The TAC system eliminates the mechanical link between the accelerator pedal and the throttle plate. The TAC system eliminates the need for a cruise control module and idle air control motor. The following is a list of TAC system components

1. The accelerator pedal assembly includes the following components: The accelerator pedal The Accelerator Pedal Position (APP) sensor The AAP sensor 2
2. The throttle body assembly includes the following components: The Throttle Position (TP) sensor 1 The TP sensor 2 The throttle actuator motor The throttle plate
3. The Engine Control Module (ECM)

The ECM monitors the driver demand for acceleration with 2 APP sensors. The APP sensor 1 signal voltage range is from about 0.7 - 4.5 V as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The APP sensor 2 range is from about 0.3 - 2.2 V as the accelerator pedal is moved from the rest pedal position to the full pedal travel position. The ECM processes this information along with other sensor inputs to command the throttle plate to a certain position.

The throttle plate is controlled with a direct current motor called a throttle actuator control motor. The ECM can move this motor in the forward or reverse direction by controlling battery voltage and/or ground to 2 internal drivers. The throttle plate is held at a 5.7° TPS rest position using a constant force return spring. This spring holds the throttle plate to the rest position when there is no current flowing to the actuator motor.

The ECM monitors the throttle plate angle with 2 TP sensors. The TP sensor 1 signal voltage range is from about 0.7 - 4.3 V as the throttle plate is moved from 0% to Wide Open Throttle (WOT). The TP sensor 2 voltage range is from about 4.3 - 0.7 V as the throttle plate is moved from 0% to WOT.

The ECM performs diagnostics that monitor the voltage levels of both APP sensors, both TP sensors and the throttle actuator control motor circuit. It also monitors the spring return rate of both return springs that the housed are internal to the throttle body assembly. These diagnostics are performed at different times based on whether the engine is running or not running.

Every ignition cycle, the ECM performs a quick throttle return spring test to make sure the throttle plate can return to the 7% rest position from the 0% position. This is to ensure that the throttle plate can be brought to the rest position in case of an actuator motor circuit failure.

Manifold Absolute Pressure Sensor Description

The Manifold Absolute Pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load and speed changes. It converts these to a voltage output.

A closed throttle on engine coast down produces a relatively low MAP output. MAP is the opposite of vacuum. When manifold pressure is high, vacuum is low. The MAP sensor is also used to measure barometric pressure. This is performed as part of MAP sensor calculations. With the ignition ON and the engine not running, the Engine Control Module (ECM) will read the manifold pressure as barometric pressure and adjust the air/fuel ratio accordingly. This compensation for altitude allows the system to maintain driving performance while holding emissions low. The barometric function will update periodically during steady driving or under a wide open throttle condition. In the case of a fault in the barometric portion of the MAP sensor, the ECM will set to the default value.

A failure in the MAP sensor circuit sets a diagnostic trouble code P0107 or P0108.

The following tables show the difference between absolute pressure and vacuum related to MAP sensor output, which appears as the top row of both tables.

MAP

MAP SPECIFICATIONS

MAP SPECIFICATIONS

VACUUM

VACUUM SPECIFICATIONS

VACUUM SPECIFICATIONS

Engine Control Module Description

The Engine Control Module (ECM), located inside the passenger kick-panel, is the control center of the fuel injection system. It constantly looks at the information from various sensors and controls the systems that affect the vehicle's performance. The ECM also performs the diagnostic functions of the system. It can recognize operational problems, alert the driver through the Malfunction Indicator Lamp (MIL) and store diagnostic trouble code(s) which identify problem areas to aid the technician in making repairs.

There are no serviceable parts in the ECM. The calibrations are stored in the ECM in the Programmable Read-Only Memory (PROM).

The ECM supplies either 5 or 12 V to power the sensors or switches. This is done through resistances in the ECM which are so high in value that a test light will not come on when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. You must use a digital voltmeter with a 10 MO input impedance to get accurate voltage readings. The ECM controls output circuits such as the fuel injectors, the idle air control motor, the A/C clutch relay, etc., by controlling the ground circuit through transistors or a device called a "quad-driver."

Knock Sensor Description

The knock sensor detects abnormal knocking in the engine. The sensor is mounted in the engine block near the cylinders. The sensor produces an AC output voltage which increases with the severity of the knock. This signal is sent to the Engine Control Module (ECM). The ECM then adjusts the ignition timing to reduce the spark knock.

Crankshaft Position Sensor Description

This direct ignition system uses a magnetic crankshaft position sensor. This sensor protrudes through its mount to within approximately 1.3 mm (0.05 in.) of the crankshaft reluctor. The reluctor is a special wheel attached to the crankshaft or crankshaft pulley with 58 slots machined into it, 57 of which are equally spaced in 6° intervals. The last slot is wider and serves to generate a "sync pulse." As the crankshaft rotates, the slots in the reluctor change the magnetic field of the sensor, creating an induced voltage pulse. The longer pulse of the 58th slot identifies a specific orientation of the crankshaft and allows the Engine Control Module (ECM) to determine the crankshaft orientation at all times. The ECM uses this information to generate timed ignition and injection pulses that it sends to the ignition coils and to the fuel injectors.

Camshaft Position Sensor Description

The Camshaft Position (CMP) sensor sends a CMP sensor signal to the Engine Control Module (ECM). The ECM uses this signal as a "sync pulse" to trigger the injectors in the proper sequence. The ECM uses the CMP sensor signal to indicate the position of the #1 piston during its power stroke. This allows the ECM to calculate true sequential fuel injection mode of operation. If the ECM detects an incorrect CMP sensor signal while the engine is running, DTC P0341 will set. If the CMP sensor signal is lost while the engine is running, the fuel injection system will shift to a calculated sequential fuel injection mode based on the last fuel injection pulse, and the engine will continue to run. As long as the fault is present, the engine can be restarted. It will run in the calculated sequential mode with a 1-in-6 chance of the injector sequence being correct.

G Sensor Description

The Engine Control Module (ECM) receives rough road information from the G sensor. The ECM uses the rough road information to enable or disable the misfire diagnostic. The misfire diagnostic can be greatly affected by crankshaft speed variations caused by driving on rough road surfaces. The G sensor generates rough road information by producing a signal which is proportional to the movement of a small metal bar inside the sensor.

If a fault occurs which causes the ECM to not receive rough road information between 50 and 132 km/h (30 and 80 mph), DTC P1391 will set.

Scheme 1

1. Relieve the coolant system pressure.
2. Disconnect the negative battery cable.
3. Disconnect the Engine Coolant Temperature (ECT) sensor connector.
4. Remove the ECT sensor from the Electronic Ignition (EI) system ignition coil adapter.

Scheme 2

1. Coat the threads of the ECT sensor with sealer.
2. Install the ECT sensor into the EI system ignition coil adapter. Tighten: Tighten the engine coolant temperature sensor to 20 N.m (15 lb-ft).
3. Connect the ECT sensor connector.
4. Fill the coolant system.
5. Connect the negative battery cable.

Scheme 3

Scheme 4

1. Disconnect the negative battery cable.
2. Disconnect the Intake Air Temperature (IAT) sensor connector.
3. Disconnect the breather hose from the valve cover.
4. Remove the air intake tube.
5. Disconnect the vacuum hoses from the throttle body.
6. Disconnect the Electric Throttle Control (ETC) connectors.
7. Disconnect the coolant hoses from the throttle body.
8. Remove the throttle body retaining nuts.