Pressure test the low-voltage cooling system on a 2024 Model S Long Range AWD to identify leaks in the powertrain/PCS coolant loop. This is a non-invasive diagnostic — do NOT open or service the HV battery thermal loop, octovalve, heat pump, or superbottle.

Warnings

Tools required

Parts

• Coolant expansion tank cap (replace if seal is suspect) × 1 — OEM Tesla expansion tank cap for Model S 2021+

Fluids

• Tesla-spec coolant (G-48 equivalent) — top-up only if level drops — 1 qt

Preparation

1. Park on level ground, place in P, engage parking brake.
2. Exit ALL doors with the key fob away from the vehicle. Wait at least 2 minutes for HV systems to fully de-energize, even on this non-HV job.
3. Disconnect the 12V low-voltage battery (located in the frunk under the nose cowl panel on 2024 Model S). Remove the cowl using plastic trim tools, then disconnect negative first.
4. DO NOT touch, cut, or pierce ANY orange cable — these are high-voltage and lethal.
5. If at any point you encounter an orange cable, an HV component, or are unsure if a system is de-energized: STOP and consult a Tesla-certified technician.
6. Allow the vehicle to sit until coolant is at ambient temperature — ideally test cold, after the car has been parked overnight.
7. Identify the low-voltage powertrain coolant expansion tank in the front compartment. Confirm it is the accessible reservoir for the front drive unit / PCS loop — NOT a sealed HV battery coolant component.
8. Visually inspect the engine bay area, radiators (front), and any exposed coolant hoses for obvious wet spots, dried coolant residue (often pink/red staining), or corrosion before pressurizing.

Procedure

1. 1

   Verify system is cold and depressurized
   Place a shop towel over the expansion tank cap and slowly turn it 1/4 turn to vent any residual pressure. If you hear hissing or see coolant weep, STOP and let the system cool further. Once stable, fully remove the cap.
   ⚠Hot, pressurized coolant can cause severe burns. Always vent before fully removing the cap.
2. 2

   Check and record baseline coolant level
   Note the coolant level relative to the MIN/MAX markings on the expansion tank. Photograph for reference. A low level before testing is itself a leak indicator. Top up only with Tesla-spec coolant (G-48 equivalent) if needed to reach normal level — do not mix with conventional green/orange coolants.
3. 3

   Install pressure tester adapter
   Select the adapter from your pressure test kit that matches the Tesla expansion tank neck. Thread or clamp it on hand-tight per the tester manufacturer's instructions. Verify the seal sits flat with no cross-threading. Connect the hand pump to the adapter.
4. 4

   Pressurize the system
   Slowly pump the system up to the rated cap pressure — do NOT exceed the pressure stamped on the OEM cap (typically printed on the cap itself; if illegible, do not exceed manufacturer-specified pressure — refer to Tesla Service Manual). Pump in slow strokes and watch the gauge.
5. 5

   Hold and observe
   Hold pressure for at least 15 minutes. Monitor the gauge: a stable needle indicates no leak. A slow drop indicates a leak — small drops can also be air bleeding into hoses, so confirm before condemning a part.
6. 6

   Visual leak inspection under pressure
   While the system is pressurized, inspect with a flashlight: front radiator(s) and end tanks, all visible coolant hoses and quick-connect fittings, the powertrain coolant pump area, the front drive unit coolant ports, and the underside of the expansion tank. Use an inspection mirror or borescope to view areas behind the front fascia. Look for fresh wet coolant, drips, or dye traces (if previously added). DO NOT trace lines into the HV battery, octovalve, or heat pump area — those are out of scope.
7. 7

   Cap pressure-hold test
   Remove the OEM cap from the tank (system already depressurized via tester) and install it on the cap-test fitting of your pressure kit. Pressurize to the cap's rated value and confirm it holds. A weak cap is a common cause of pressure loss and over-temperature warnings on Model S.
8. 8

   Release pressure and remove tester
   Use the relief valve on the pump to slowly bleed off pressure. Once the gauge reads zero, remove the adapter. Wipe any residual coolant from the tank neck.
9. 9

   Document findings
   Record: starting level, pressure applied, time held, ending pressure, and any leak locations identified. If a leak is found, plan the repair as a separate procedure — do not attempt repairs on HV-loop components.

Reassembly

1. Reinstall the OEM expansion tank cap (or a new one if the cap failed its hold test). Tighten by hand to the stop — do not use tools.
2. Top up the coolant to the proper level with Tesla-spec coolant if any was lost during testing.
3. Reinstall the frunk nose cowl panel and any clips removed for 12V access. Air box clips: torque to spec — refer to Air Box Clips torque value if any were disturbed.
4. Reconnect the 12V low-voltage battery (positive first, then negative). Ensure terminals are clean and tight — torque to OEM specification — refer to Tesla Service Manual.
5. Close the frunk and verify it latches fully.

Verification

• After reconnecting 12V, allow the car to wake fully (touchscreen boots, no persistent error icons).
• Check the touchscreen for any 'Powertrain' or 'Coolant Level Low' alerts. Clear or note any that appear.
• Take the vehicle for a 10–15 minute drive including some highway speed to bring the powertrain coolant loop up to operating temperature.
• Park, allow to cool, and re-inspect the expansion tank level and previously suspect areas for any new wet spots.
• Tesla recommends inspecting battery/powertrain coolant at 4 years / 50,000 mi — record this pressure test in the service log so the next inspection can be scheduled accordingly.
• If the system failed to hold pressure and no external leak was found, do NOT assume an internal HV-loop leak and attempt repair — refer the vehicle to a Tesla-certified technician for further diagnosis (octovalve, heat pump, or battery chiller leaks require HV training).

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