DME Temperature Gauge and Sensor – Information, Troubleshooting, and Testing – 2.5L NA

Overview

This procedure outlines how to troubleshoot and test the DME temperature sensor on all Porsche 944 variants with an 8-valve engine configuration. The DME (Digital Motor Electronics) temperature sensor provides critical data to the engine control unit, affecting fuel mixture and engine performance. Incorrect sensor readings can cause rich or lean fuel mixtures, impacting drivability. This guide tests the sensor’s resistance to ensure accurate operation, applicable to both pre-1985.5 (1982–85) and 1985.5 onwards (1985.5–88) models. Note that this procedure assumes the dashboard coolant temperature gauge is functioning correctly, as it is used as a reference during testing.

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Tools Required

• Multimeter
• Test Leads
• 19mm (3/4 inch) wrench

Parts Required

• DME temperature sensor (if replacement is needed): 944 606 125 00

Step-by-Step Procedure

Step 1: Prepare for Testing

1. Park the vehicle on a flat surface and engage the parking brake.
2. Turn the ignition switch to the OFF position to ensure safety.
3. Locate the DME temperature sensor on the engine block, near the coolant temperature sensor, typically on the driver’s side near the cylinder head.

Step 2: Disconnect the DME Computer Connector

4. Locate the DME computer, usually under the passenger-side dashboard or in the engine compartment (depending on model year).
5. Disconnect the DME computer electrical connector carefully to avoid damaging the pins.

Step 3: Test Sensor Resistance at Ambient Temperature

6. Connect a multimeter, set to measure resistance (ohms), between terminal 13 on the disconnected DME plug and a grounding point in the engine compartment (e.g., a clean metal surface on the engine block).
7. Measure the resistance and compare it to the following values for ambient temperatures:

• 15–30 °C (59–86 °F):

• At 15 °C (59 °F): Approximately 3.3 k-ohms (3300 ohms)

• At 30 °C (86 °F): Approximately 1.46 k-ohms (1460 ohms)

Step 4: Test Sensor Resistance at Operating Temperature

8. Reconnect the DME computer electrical connector.
9. Start the engine and run it until the dashboard coolant temperature gauge indicates approximately 80 °C (176 °F). If the dashboard gauge is suspected to be faulty, use a non-contact thermometer to verify the engine block surface temperature near the DME sensor.
10. Turn the engine off and immediately disconnect the DME computer electrical connector again.
11. Connect the multimeter between terminal 13 on the DME plug and ground, as in Step 3.
12. Turn the ignition switch to the ON position without starting the engine and verify the dashboard gauge still reads approximately 80 °C (176 °F).
13. Measure the resistance and compare it to the expected value: 80 °C (176 °F): 280–360 ohms

Step 5: Evaluate Results and Next Steps

14. If the measured resistances match the specified values (within ±10% tolerance), the DME temperature sensor is functioning correctly.
15. If the resistances are higher than specified (e.g., >360 ohms at 80 °C), the sensor may cause a richer fuel mixture and should be replaced with a new unit (944 606 125 00).
16. If the resistances are lower than specified (e.g., <280 ohms at 80 °C), the sensor may cause a lean fuel mixture and should be replaced.
17. To replace the sensor, use a 19mm (3/4 inch) wrench to remove the old sensor and install the new one. Torque to 30 Nm (22 ft-lbs).

Post Procedure Checklist

• Verify all electrical connections to the DME computer and sensor are secure.
• Check for any loose tools or debris in the engine compartment or under the dashboard.
• Start the engine and monitor the dashboard coolant temperature gauge to ensure it reads 80–90 °C (176–194 °F) during normal operation.
• Observe engine performance for signs of incorrect fuel mixture (e.g., rough idle, poor acceleration), indicating a potential sensor issue.
• Check for coolant leaks around the sensor after replacement.

Sources

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