Chapter 14 Troubleshooting Electronic Control System Problems 353 Copyright by Goodheart-Willcox Co., Inc. Testing Manual Valve Position Sensors Note: Some manual valve position sensors are called range sensors, PRNDL switches, or position switches. An ohmmeter can be used to test the manual valve position sensor. Check the resistance at each switch posi- tion. Resistance should change as the shift lever is moved. See Figure 14-21. If resistance is not within specifications or does not change when the shifter is moved, the sensor should be replaced. Some manual valve position sensors can be checked with a scan tool. The sensor should be connected for this test. Follow the scan tool menu directions to test the sensor. Testing Throttle Position Sensors Before testing the throttle position sensor, determine what type of sensor it is. Most throttle position sensors are resistor types and can be tested with an ohmmeter. To make an ohmmeter check, disconnect the sensor wiring harness connector. Then attach an ohmmeter to the proper sensor leads. Operate the throttle and observe the ohmmeter read- ings. Many manufacturers specify checking the resistance at idle and wide open throttle positions. If the readings are incorrect, or if the ohmmeter readings do not change steadily as the throttle is opened, the sensor is defective. Some throttle position sensors are transducers and must be checked with a voltmeter. A special adapter must Component Testing The following sections explain how to test individual components. Other component testing procedures will be found in the appropriate vehicle service information. Figure 14-19. To check an electronic transmission component through the case connector, you must know which connector pin goes to which component. A connector diagram, such as the one shown here, can be very helpful. (General Motors) A B C D E L M T N P R S P.E.D. 3 Transmission Pass-thru Connector Cavity Function A 1-2 shift solenoid (low) B 2-3 shift solenoid (low) C Pressure control solenoid (high) D Pressure control solenoid (low) E Both shift solenoids, TCC solenoid, and 3-2 control solenoid (high) L Transmission fluid temperature (high) M Transmission fluid temperature (low) N Range signal “A” P Range signal “C” R Range signal “B” S 3-2 control solenoid (low) T TCC solenoid (low) Figure 14-20. To make an amperage check of a solenoid on the vehicle, you must know what the current draw is supposed to be. Compare the correct reading in a table like this with actual current draw to determine whether the solenoid is good. (General Motors) Pressure control solenoid current (amp) Approximate line pressure (psi) 0.02 170–190 0.10 165–185 0.20 160–180 0.30 155–175 0.40 148–168 0.50 140–160 0.60 130–145 0.70 110–130 0.80 90–115 0.90 65–90 0.98 55–65