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Matt, Engineer
Category: Chevy
Satisfied Customers: 21990
Experience:  Honors degree in Mechanical Engineering, worked 8 years as a Formula 1 engine engineer.
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The check engine light came on my 2008 chevy silverado 2008

Customer Question

The check engine light came on my 2008 chevy silverado 2008 v6. It shifts hard from time to time and will stop out of no where and run normal. The silid light under the park, nuetral shifts etc goes out also when it starts acting up and shifting hard. The code that came up was the p1815 code. I replaced the nuetral safety switch ( GM product) and speed sensor also. It still does the same thing. The same code comes up p1815 manufacturer module. Can you please help me?
Submitted: 1 year ago.
Category: Chevy
Expert:  Matt replied 1 year ago.


my info shows P1815 : Transmission Fluid Pressure (TFP) Valve Position Switch- Start In Wrong Range

so I'd begin by replacing the transmission fluid with fresh

Also check its level with the gearbox warm and just after you've moved the selector through all the positions leaving it for a few seconds in each one and then back to park.

You can top up the box through the side fill plug if required and make sure you use the correct oil for your car as the fluids are not all the same. Some manufacturers recommended a change of the type of fluid - Speak to the local dealer and parts dept - they will advise you on the updated fluid to use..

Expert:  Matt replied 1 year ago.


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