DME Relay Technical Testing

Overview

This guide explains how to test and troubleshoot the DME relay on a Porsche 944 S / S2 with a 16v engine. The DME relay powers the engine control unit (DME) and the fuel pump. If it fails, your car won’t start, making this a critical component to check if you’re having starting issues. This procedure includes testing the relay, making an emergency jumper to get you home, and repairing the relay if needed.

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Tools Required

• 2 wire leads with female spade connectors on one end (for testing)
• 3-lead emergency jumper with male spade connectors on each lead (for emergencies and testing)
• Multimeter (for testing relay)
• 12 VDC power supply (for testing relay)
• Magnifying glass (for repairing relay)
• Soldering iron and solder (for repairing relay)
• Paperclip (optional, for alternative emergency jumper)

Parts Required

• DME relay for Porsche 944 S / S2 (if replacement is needed) 944 615 115 00
• Replacement diode (available at electronics stores like Radio Shack, if repairing relay)

Required Additional Procedures

Steps in these procedures are required to complete this process:

• Fuse and Relay Panel Access (for locating and removing the DME relay)

Step-by-Step Procedure

1. Testing the DME Relay

1. Locate the DME relay on the relay/fuse panel under the hood of your Porsche 944 S / S2. It’s labeled as G5. Follow this link to ensure this step – Fuse and Relay Panel Access – of the process is followed accurately.
2. Remove the DME relay from its socket by pulling it straight out.
3. Set your multimeter to measure resistance (ohms).
4. Check the resistance across terminals 30 and 87b on the relay (labeled on the bottom). You should see infinite resistance (a “1” or “OL” on a digital multimeter).
5. Check the resistance across terminals 30 and 87. This should also show infinite resistance.
6. Connect a 12 VDC power supply across terminals 85b and 87. Measure resistance across terminals 30 and 87b again—it should now be near zero (0.1 to 0.3 ohms).
7. Connect the 12 VDC power supply across terminals 85 and 86, with the negative lead on 85 and positive on 86 (due to the diode). Measure resistance across terminals 30 and 87—it should be near zero (0.1 to 0.3 ohms).
8. If any readings are incorrect (e.g., not infinite when unpowered or not near zero when powered), the relay is faulty and needs repair or replacement.

2. Emergency Jumper Installation

9. If the car won’t start and you suspect the DME relay, create an emergency jumper with three leads, each with a male spade connector.
10. Insert one spade connector into terminal 87 on the relay socket.
11. Insert the second spade connector into terminal 87b.
12. Insert the third spade connector into terminal 30. You should hear the fuel pump start running.
13. Start the car using the ignition switch. Remove the jumper when the car is off to avoid draining the battery.

Alternative: If you don’t have wire, wrap a paperclip around terminals 30, 87, and 87b, then reinstall the relay to temporarily bypass the fault.

3. Inspecting and Repairing the DME Relay

14. Remove the plastic cover from the DME relay by pulling the bottom lip outward and lifting the cover off the tabs.
15. Use a magnifying glass to inspect all solder joints inside the relay for cracks.
16. Heat your soldering iron and resolder any cracked joints. For best results, resolder all joints since factory soldering can be weak.
17. Replace the diode in the primary relay circuit if it looks damaged (use a compatible diode from an electronics store).
18. Reattach the cover and retest the relay using the steps in “Testing the DME Relay” above.

Post Procedure Checklist

• Ensure the car starts reliably after testing or repairing the relay.
• Check that the fuel pump runs when the jumper is installed (if used) and stops when removed.
• Verify no battery drain occurs when the car is off and the jumper is removed.
• Listen for unusual noises from the relay or fuel pump during operation.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manual, Volume 1
• YouTube