In order to determine if the throttle position sensor signal and brake switch signal are being received by the ECU, place the ignition switch to the ON position with the engine off, connect a digital voltmeter to the diagnostic check connector and slowly depress the throttle. On models prior to 1987, if the vehicle does not have a diagnostic check connector in the engine compartment, connect the voltmeter to the DG Terminal. Its location can be found in the appropriate repair manual.
The ECT terminal can be designated as TT or T1 depending on the vehicle model. The position in the diagnostic check connector remains the same. The voltage will increase in one volt increments from 1 to 8 volts as the throttle is slowly opened. To verify the brake signal, apply the brake pedal while the throttle is wide open. The voltage displayed on the voltmeter screen will go to zero.
If the voltage readings progress in a step-like fashion, it indicates proper operation of the following:
Circuit integrity from the sensor to the ECU
Circuit integrity from the ECU to the diagnostic check connector.
If the voltage remains at 0 volts as the accelerator is depressed, possible causes are:
• Brake signal remains on.
• ECU power supply circuit.
The voltage chart above provides a voltage value for the corresponding throttle opening. This can be used to establish accelerator position for a given throttle opening.
To check for shift timing while the vehicle is driven, connect a voltmeter and drive the vehicle. Voltage will increase in one volt increments from 0 to 7 volts. These voltage signals are output from the ECU to indicate a response to system sensors. The lock-up voltages in second and third gear may not be consistently output with throttle opening under 50%. In order to output each voltage signal, the throttle will need to be open greater than 50%. If the gears fail to shift in response to the changes in voltage readings, the solenoids may be sticking or the electrical circuit to the solenoid may have an open.
Terminal Voltage and Gear Position
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