Gasoline Engine Communication Signals 2 of 2


1. Stop lamp switch

The signal from the stop lamp switch is used to detect brake operation. The STP signal voltage is the same as the voltage supplied to the stop lamp as shown in the illustration.

2. EGR gas temperature sensor

The EGR gas temperature sensor is installed inside the EGR valve and uses a thermistor to measure the EGR gas temperature.

3. Fuel control switch or connector

The fuel control switch or connector notifies the engine ECU of whether the gasoline that is being used is regular or premium.


Some models use a fuel control connector in place of a fuel control switch. This connector should be connected when premium gasoline is used, and is disconnected when regular gasoline is used. In other models, this is reversed. For information regarding the connector position or the regular/premium gasoline switching method, refer to the Owners Manual.

4. Water temperature switch

The water temperature switch is attached to the cylinder block, and turns ON when the coolant temperature become high.

5. Clutch switch

The clutch switch is under the clutch pedal and detects whether or not the clutch pedal is being fully depressed.

6. HAC (High-Altitude Compensation) sensor

The HAC sensor detects changes in the atmospheric pressure. The construction and operation are the same as those of the manifold pressure sensor. This sensor is sometimes in the engine ECU and sometimes outside of it. When driving at high altitude, the atmospheric pressure decreases as does the air density. Thus, L-type EFI engines, except those with hot-wire type air flow meters, tend to make the air-fuel mixture rich. The HAC sensor compensates for this deviation in the airfuel ratio.

7. Vapor pressure sensor

The vapor pressure sensor measures the pressure of the fuel vapor in the fuel tank. The basic construction and operation of the sensor are the same as those of the manifold pressure sensor. Unlike the output characteristic of that sensor, however, the vapor pressure sensor can detect slight changes in vapor pressure.

8. Turbocharging pressure sensor

The turbocharging pressure sensor detects the intake manifold pressure that is charged by the turbocharger. The basic construction and operation of the sensor are the same as those of the manifold pressure sensor. If the intake manifold pressure charged in the turbocharger becomes extremely high, the engine ECU will cut the fuel supply to protect the engine.

9. Oil pressure switch

The oil pressure switch signal is used to determine the low engine oil pressure. The oil pressure signal is used to control the ISC system. When the oil pressure is low, the lubrication and cooling of the engine components will be hindered. Therefore, the engine ECU will increase idling speed, etc., to restore the oil pressure to the normal level.

10.Kick-down switch

The kick-down switch is also called the full-throttle switch, and it is directly installed beneath the floor panel of the accelerator pedal.

Diagnostic Terminal

When the engine ECU stores a DTC (Diagnostic Trouble Code) in memory, the DTC must be checked and repairs must be performed. The DLC contains a DLC3 SIL terminal, which is required to display the DTC to communicate directly with the engine ECU when the handheld tester is used, TE1, TE2, E1, TC and CG terminals which cause the MIL to flash.

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