1989 Geo Spectrum 2D Hatchback, AutomaticFACTORY OEM SERVICE PROCEDURE

System Performance Test 2 (Dwell Fixed Less Than 15 Degrees Spectrum)

  1. Ground ALDL test terminal located near left kick panel. With engine at part throttle, choke engine. If dwell does not change, go to step 2). If dwell increases, check for vacuum leak, exhaust leaks before O2 sensor, vacuum hose routing and EGR operation. If no leaks are found, repair carburetor.
  2. Disconnect O2 sensor. Connect positive side of flashlight battery (1-1.7 volts) to the O2 sensor ECM side of connector. Simulate O2 sensor signal voltage by grounding negative side of flashlight battery. Note dwell at part throttle. If dwell is less than 15 degrees, go to step 3). If dwell increases, check for open from ECM terminal No. 3. If okay, replace O2 sensor.
  3. Stop engine, turn ignition on and measure voltage between ECM terminals No. 17 and 22. If less than 3 volts, go to step 4). If greater than 3 volts, check coolant sensor circuit.
  4. Check for open circuit from ECM terminal No. 20 to ground and check for grounded wire to ECM terminal No. 3. If okay, check voltage from ECM terminal No. 5 to ground.
  5. If voltage is less than 2 volts, go to step 6). If voltage is greater than 2 volts, check for open from ECM terminals No. 22 to TPS terminal "C". If okay, repair ECM connector or replace ECM.
  6. Check voltage at ECM terminal No. 7. Voltage should be 5 volts, if not, replace ECM. If voltage is okay, check wiring between ECM terminal No. 5 and TPS terminal "B", and ECM terminal No.7 and TPS terminal "C". If wiring is okay, adjust or replace TPS.
Fig 1: Coolant Sensor, O2 Sensor & TPS Wiring Diagram
G121715Courtesy of GENERAL MOTORS CORP.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.