Chapter 14 Troubleshooting Electronic Control System Problems 361 Copyright by Goodheart-Willcox Co., Inc. checked with a scan tool. Some manufacturers recommend checking the resistance of the speed sensor winding. Pressure sensors can usually be checked with an ohm- meter. If a normally closed sensor reads infinite resis tance with no pressure applied, the sensor is defective. If a nor- mally open sensor reads low resistance with no pressure applied, it is defective. To test temperature sensors, check the resistance read- ing at various temperatures. If the readings are not within specifications, the sensor is defective. Many sensors read incorrectly only in certain temperature ranges. To check a MAP sensor, attach a voltmeter and vacuum pump to the sensor. If MAP sensor voltage reading increases with increases in vacuum, the MAP sensor is probably good. There are several types of mass airflow (MAF) sensors. Test procedures vary with each type. Always disconnect the MAF wiring to make readings. Testing oxygen sensors requires care, since oxygen sensors are sensitive to excess current flow. Some manufacturers do not recommend meter tests of the oxygen sensor. Oxygen sensors use either Zirconia or Titania elements. Oxygen sensors with one or two lead wires are non-heated types. If an oxygen sensor has three or more leads, it is a heated type. The sensor must be at its operating temperature before testing it. To test an output solenoid, remove the solenoid wiring harness and measure solenoid resistance. Some solenoids can be operated with jumper wires. Full battery voltage may destroy other solenoids, so always check the manufacturer’s specifications before trying this test. Schematics are useful when looking for defective wires, connections, and devices. Always obtain the proper wiring diagram when checking for a wiring problem. Some manufacturers have procedures or equipment for testing for proper ECM voltage outputs. On most vehicles, a scan tool can be used to test the ECM. The ECM may have to be tested by substituting a known good unit and rechecking system operation. Always double-check your results before replacing a defective component. Review Questions—Chapter 14 Answer the following questions using the information provided in this chapter. 1. Electronically controlled transmission or transaxle problems often resemble those that occur in _____ transmissions. 2. A pattern failure is a _____ type of problem. 3. _____ are the most common cause of electronic transmission/transaxle problems. 4. On-off _____ _____ can stick open or closed. 5. On a few electronic transmissions, some shifts are _____ controlled. 6. Engine missing is often confused for lockup torque converter _____. 7. Do not remove any _____ until you have retrieved trouble codes from the ECM. 8. Where are fusible links usually located? 9. Scan tools can be thought of as a portable _____ that can communicate with the vehicle’s ECM. 10. OBD I computer systems can have a maximum number of _____ trouble codes. The OBD II system can have as many as _____ potential codes. 11. The snapshot is a scan tool feature that records vehicle operating conditions just before and just after a _____ occurs. 12. The three ways of checking computer control systems are _____ checks, _____ tests, and testing by _____. 13. Speed sensors produce a(n) _____ current output. 14. If a normally closed (NC) sensor reads zero resistance, it is _____. 15. If the MAP voltage reading increases with increases in _____, the sensor is probably OK. 16. The three types of MAF sensor outputs are analog _____ voltage, low _____ pulse, or high _____ pulse. Matching Match the following test equipment or testing method with the device that it is best at testing. 17. Jumper wires _____ 18. Ohmmeter _____ 19. Substitution _____ 20. Waveform meter _____ (A) Temperature sensor (B) Speed sensor (C) Output solenoid (D) ECM (E) Th rottle position sensor