Checking the internal mode switch (transmission gear selection)?

2005 CHEVROLET IMPALA

260,000 MILES • 3.4L • V6 • 2WD • AUTOMATIC

MRTONEG

MEMBER
22 POSTS

I am having a no crank no start condition and have narrowed it down to either the internal mode switch, or the ECM/PCM and the BCM needing replaced and programmed. When I turn the ignition switch to on/start the gears that show up are P, R,3,2 and the N,D,1 do not light up the border around it showing the gear selected like the other gears do. To test the internal mode switch can I just test the wires on the top of the transmission at the connector on top, or will I need a special tool since the internal mode switch is inside of the transmission? Please help!

Jan 9, 2023 at 4:16 AM

JACOBANDNICKOLAS

✓Experienced Mechanic
110,246 POSTS

Hi,

If you are seeing P, R, 3, 2 only, chances are it is the transmission range sensor. However, before we start replacing expensive modules and the switch, what needs to be done is the system needs the can-bus scanned.

CAN stands for controller area network. Basically, the different modules are tied together via a few wires. This type of scan will identify diagnostic trouble codes regardless of the module storing them.

Here is a link that shows how it's done:

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

If you look below, I attached the wiring schematic for the transmission, so you have a reference.

Let me know your thoughts or if you have other questions.

Take care,

Joe

See pics below.

Images (Click to enlarge)

Jan 9, 2023 at 6:58 AM

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Checking the internal mode switch (transmission gear selection)?

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