Transmission temperature gauge drops quickly down causing the check gauge light to come on and overdrive light to flash

Do you mean transmission pressure gauge goes low?

First thing you will need to do is to replace the temperature sensor it is not reading properly.

Hi,

Based on your description, it sounds like a bad connection, but other things can cause the problem such as the sensor. However, I will tell you, this is not an uncommon issue. In most cases, it is caused by a loose connection on the wiring harness going to the transmission.

What I have done is provide a diagnostic flow charts. What I suggest is to start at number 1 and work your way through. In addition to the flow charts are pics that show pin layouts for the connectors relevant to the testing.

If you look at the last two pics, I broke out the specific 12 pin connector which includes power and ground for the temp sensor.

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Here are a few links you may find helpful when testing:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

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Let me know if this helps or if you have other questions. Also, if you have a chance, let me know what you find.

Take care,
Joe