Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSSAAB1991900 SE, STANDARDREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - SYSTEM/COMPONENT TESTSIGNITION SYSTEMTIMING CONTROL SYSTEMSKNOCK SENSOR
1991 Saab 900 SE, Standard
Knock Sensor
1991 Saab 900 SE, StandardSECTION Knock Sensor
- 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.
- 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.
- 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).
- 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.
- 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.
- 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.
RENDER: 1.0x
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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.