Excessive Battery Discharge Rate – 2.5L NA

Overview

This procedure helps diagnose and resolve excessive battery discharge in all Porsche 944 variants with an 8-valve engine. Excessive discharge can drain the battery, preventing the car from starting. The normal discharge rate with the ignition off and key removed should be less than 60 mA. If it exceeds 65 mA, this guide will help identify the cause, such as faulty components or circuits, for both pre-1985.5 and 1985.5 onwards models.

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Tools Required

• Digital multimeter
• Test leads

Step-by-Step Procedure

Step 1: Prepare the Battery and Multimeter

1. Disconnect the positive battery lead from the battery terminal. The battery is a BCI Group 41 size, measuring 284 mm (11-3/16 inches) L x 175 mm (6-7/8 inches) W x 175 mm (6-7/8 inches) H, typically rated at 50–70 amp-hours.
2. Connect the digital multimeter between the positive battery lead and the positive battery terminal.
3. Set the multimeter to the ammeter function and turn it on.

Step 2: Measure the Battery Discharge Rate

4. Check the multimeter reading. The discharge rate should be less than 65 mA (0.065 A).
5. If the discharge rate is 65 mA or lower, the battery discharge is within normal limits, and no further action is needed.

Step 3: Identify Causes of High Discharge Rate

6. If the discharge rate exceeds 65 mA, begin troubleshooting by removing fuses one at a time from the fuse box.

For Pre-85.5 models:

• Refer to the factory wiring diagrams for fuse locations and associated circuits. Follow this link to ensure this step – Factory Wiring Diagrams – is followed accurately.

For 85.5 Onwards models:

• Refer to the updated factory wiring diagrams for fuse locations and associated circuits. Follow this link to ensure this step – Factory Wiring Diagrams – is followed accurately.

7. After removing each fuse, note how much the discharge rate decreases on the multimeter.
8. Reinstall the fuse before moving to the next one.
9. Repeat the process for relays, removing and reinstalling them one at a time, noting any decrease in discharge rate.

Step 4: Isolate the Faulty Component

10. Identify the fuses or relays where removing them caused a significant decrease in discharge rate.
11. Using the factory wiring diagrams, determine all components powered by those fuse or relay circuits.

For Pre-85.5 models:

• Follow this link to ensure this step – Factory Wiring Diagrams – is followed accurately.

For 85.5 Onwards models:

• Follow this link to ensure this step – Factory Wiring Diagrams – is followed accurately.

12. Disconnect components in those circuits one at a time, checking the multimeter after each disconnection.
13. Stop when the discharge rate drops significantly, indicating the faulty component causing the high current draw.

Post Procedure Checklist

• Verify the discharge rate is below 65 mA with all fuses and relays reinstalled.
• Ensure all disconnected components are reconnected properly.
• Check that the battery terminals are secure and free of corrosion.
• Test the vehicle by starting it to confirm normal operation.

Sources

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