Allison Transmission Leaking from Wiring Harness [02 Reasons Why This Issue Arises]

A transmission wiring harness is located under the driver’s side of the car.

In many GM cars, the Allison transmission leaks from the wiring harness, and people want to fix it.

If fluid leaks from the wiring harness, it creates a communication gap between the transmission and ECU and causes slow transmission response and faulty codes.

It becomes challenging for a general driver to find out what is actually causing the problems.

In this article, I have discussed why Allison transmission fluid leaks from wiring harnesses and how to fix the problem.

Allison Transmission Leaking from Wiring Harness [02 Basic Reasons]

02 basic problems cause Allison transmissions to leak from the wiring harness due to O-rings that do not fit right or are broken or damaged.

Let’s discuss them in detail.

01. Loose Fitting

Loose Fitting

Sometimes the setting isn’t right after unplugging the wiring harness and plugging it back in.

Sometimes reconnecting the harness pushes the shifter plug back in.

The adapter plug housing connects the transmission and wiring harness.

So checking the adapter plug housing assembly is essential.

If there is already a problem in the assembly, the transmission can leak from the connector.

02. Damaged or Broken O-Ring

Damaged or Broken O-Ring

Damaged or broken wiring harness O-rings are the most common cause of Allison transmission leaks from the wiring harness.

O-rings serve as a seal between the dry and wet areas.

When the O-ring breaks, you may find a few drops of fluid in the wiring harness.

How to Fix Allison Transmission Leaking from Wiring Harness

When the Allison transmission leaks from the wiring harness, it slows down the transmission, makes it hard to shift gears, and gives out wrong codes.

The transmission leaks from the wiring harness must be fixed to eliminate such issues.

Buy a bottle of fluids before you start because you’ll need them afterward.

For the fixing process, you’ll also need a plastic clip.

Let’s start the fixing process step by step:

  1. Put your car in parking mode and set the emergency brake.
  2. Now, lift the front parts of the vehicle and place two jack stands under each wheel.
  3. Disconnect the negative battery cable.
  4. Under the car, you can wear safety glasses to protect your eyes.
  5. Remove the metal cover now.
  6. You can use a socket and ratchet to remove the metal cover; the socket’s diameter will differ depending on the vehicle’s make and model.
  7. Once you’ve removed the bolt, pull down the metal shoe.
  8. Remove the dust cover cap.
  9. If any fluid leaks, put a drink pan underneath.
  10. Lose the connector using a screwdriver, turn it anticlockwise, and remove it.
  11. With a towel, clean the connector properly; compressed air can also be used.
  12. Now remove the center screw of the adapter plug housing using a 7-mm socket and ratchet.
  13. Now remove the O-ring and clean the cavity.
  14. Put a brand-new O-ring over the connector and lubricate it with fresh transmission fluid.
  15. Before reinstalling the connector, make sure it is properly locked and snapped.
  16. When installing the connector, ensure the pins go in the right place and do it correctly.
  17. Now lower the vehicle and check the fluid level using a dipstick; add the required amount of fluids if the level is low.

If the transmission harness connector is too old or damaged, replace it.

The replacement cost of the connector is between $28 and $70, depending on the vehicle’s model year.

Using this method, you will be able to fix the transmission leak that is coming from the wiring harness.

Final Thoughts

Now you know what causes your transmission to leak from the wiring harness and how to solve it.

I recommend you take your vehicle to a repair shop if you face problems repairing the connector yourself.

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