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Home >> Geo >> 1991 >> Prizm Base, 4D Hatchback, Standard >> Repair and Diagnosis >> Transmission >> Automatic Trans >> Diagnosis - A-240 "E" Series >> Symptom Troubleshooting >> Transmission Will Not Shift

Transmission Will Not Shift

  1. Warm engine to normal operating temperature. Locate check connector near left strut tower in engine compartment. See Figure . Install Digital Volt-Ohmmeter (DVOM) between cavities No. 3 and 17 of check connector. See Figure .
  2. Turn ignition on. Note that voltage changes with throttle opening. If voltage changes with throttle opening, proceed to step 6). If voltage does not change with throttle opening, proceed to step 3).
  3. Obtain access to ATCM, located near center console. See Figure . Note ATCM electrical connector terminal identification. See Figure . Using DVOM, backprobe cavities No. 19 and 22 of ATCM electrical connector with connector installed on ATCM. See Figure .
  4. No voltage should exist with brake pedal released. Approximately 10-14 volts should exist with brake pedal depressed. If voltage is not as specified, check for defective brakelight switch or wiring circuit.
  5. If voltage is as specified, check for defective ATCM power source or ground connections. Check for defective throttle position sensor or wiring.
  6. Ensure ignition is off. Disconnect electrical connector from ATCM. Road test vehicle and ensure transmission gear changes corresponds with shift lever position. See GEAR CORRESPONDENCE table. If abnormality exists, a mechanical transmission problem exists.
    GEAR CORRESPONDENCE

    Shift Lever Position Transmission Gear
    "D" Overdrive
    "2" 3rd Gear
    "L" 1st Gear
  7. If all gears are correct, turn ignition off. Reconnect ATCM electrical connector. Install DVOM between cavities No. 3 and 17 of check connector. See Figure .
  8. Road test vehicle and ensure voltage increases from zero to 7 volts. If no voltage exists, proceed to step 10). If voltage increases from zero to 7 volts, transmission or solenoid is faulty. If voltage increases from zero to 5 volts, perform NO UPSHIFT TO OVERDRIVE  under SYMPTOM TROUBLE SHOOTING.
  9. If voltage increases from zero to 3 volts, check for 10-14 volts between cavities No. 19 and 21 of ATCM electrical connector with connector installed and shift lever in "D" position. See Figure . If 10-14 volts exist, check for defective neutral start switch or wiring circuit. If 10-14 volts do not exist, replace ATCM.
  10. Check for 10-14 volts between cavities No. 19 and 20 of ATCM electrical connector with connector installed and shift lever in "D" position. See Figure . If 10-14 volts exist, check for defective neutral start switch or wiring circuit. If 10-14 volts do not exist, replace ATCM.
NOTE: It may be necessary to clear fault codes from ATCM memory, as disconnecting ATCM electrical connector and road testing vehicle may set a fault code. See CLEARING FAULT CODES  under TRANSMISSION TESTING.
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