Oxygen Sensor Testing and Replacement

Overview

The oxygen sensor (O2 sensor) in your Porsche 944 (16v engine) monitors the oxygen levels in the exhaust to help the Digital Motor Electronics (DME) adjust the fuel mixture for optimal performance. A properly functioning O2 sensor ensures better fuel economy, lower emissions, and smoother engine operation. This guide covers general information, testing, and replacement of the three-wire heated O2 sensor specific to the 944, which should be replaced every 60,000 miles (96,560 km). Testing helps diagnose a faulty sensor, while replacement restores efficient engine performance.

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Tools Required

• 24mm (15/16 inch) open-end wrench or O2 sensor socket
• Voltmeter
• Propane source (for testing)
• Crimp tool
• Wire connectors

Parts Required

• Oxygen sensor – 944 606 135 02 or universal replacement – 13913 or 15735
• Crimp-type wire connectors (if using universal sensor)

Step-by-Step Procedure

Step 1: Test the Oxygen Sensor

1. Start the car and let it run until the engine reaches normal operating temperature.
2. Locate the O2 sensor connector plug at the back of the engine. Disconnect it.
3. Connect a voltmeter to the sensor’s signal wire in the plug.
4. Run the engine at approximately 2,500 RPM.
5. Introduce propane into the intake to enrich the fuel mixture until the engine RPM drops by about 200 RPM. Alternatively, disconnect the vacuum line to the fuel pressure regulator, but plug the line to prevent a vacuum leak.
6. Check the voltmeter. If the reading rises quickly to above 0.9 VDC, the sensor correctly detects a rich mixture. If the response is slow or stays below 0.8 VDC, replace the sensor.
7. Stop adding propane and secure the source.
8. While maintaining 2,500 RPM, disconnect a vacuum line from the intake to create a lean mixture.
9. Check the voltmeter. If the reading drops quickly to below 0.2 VDC, the sensor correctly detects a lean mixture. If the response is slow or stays above 0.2 VDC, replace the sensor.

Step 2: Replace the Oxygen Sensor

10. Locate and disconnect the O2 sensor connector plug at the back of the engine. If needed, trace the wire from the sensor to find the plug.
11. Locate the O2 sensor on the exhaust system and remove it using a 24mm (15/16 inch) open-end wrench or O2 sensor socket.

If installing a universal sensor:
Follow the manufacturer’s instructions for splicing the factory connector plug onto the new sensor or installing the provided connector kit. Use crimp-type connectors, not solder, to ensure the sensor functions correctly by drawing clean air through the wire strands.

12. Install the new O2 sensor and tighten it to 50 Nm (37 ft-lbs).
13. Reconnect the sensor’s connector plug.

Avoid using silicon-based chemicals (e.g., RTV sealants, anti-seize compounds) near the sensor, as silicon can contaminate it and cause failure. Check product labels before use.

Post Procedure Checklist

• Start the engine and check for exhaust leaks around the new sensor.
• Drive the car for 5 miles (8 km) to allow the DME to adjust to the new sensor.
• Monitor for symptoms like engine surging, poor fuel economy, or strong exhaust odors, which may indicate improper installation or a defective sensor.
• Verify the check engine light (if equipped) is off after driving.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manuals
• Youtube