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Home >> Saab >> 1991 >> 900 SPG >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Ignition System >> Timing Control Systems >> Knock Sensor
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Knock Sensor

  1. Connect timing light. With engine running at a fast idle, tap cylinder head with a plastic mallet. If timing retards, knock sensor is okay. If timing does not retard, turn ignition off. Go to step 2) for 900 Series vehicles, or to step 4) for 9000 Series vehicles.
  2. Locate knock sensor under intake manifold. Unplug connectors from sensor and ignition ECU. Check Green wire for continuity between harness connector and ignition ECU pin No. 13. Also check Green wire for short to ground, to Brown wire, or to shield.
  3. Check Brown wire for continuity between harness connector and ignition ECU pin No. 12. Also check Brown wire for short to ground, to Green wire, or to shield. Ensure there is continuity between shield and ground. Replace wire assembly if defective. Go to step 6).
  4. Locate knock sensor under intake manifold. Unplug connectors from sensor and ignition ECU. Check Gray wire for continuity between harness connector and ignition ECU pin No. 11. Also check Gray wire for short to shield or to ground.
  5. Check shield for continuity between sensor harness connector and ignition ECU pin No. 30. Check shield for short to ground. Replace wire assembly if defective.
  6. Temporarily replace knock sensor with a known good one. Repeat step 1). If timing still does not retard, reinstall original sensor and replace ignition ECU.
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