Checking the internal mode switch (transmission gear selection)?

MRTONEG

MEMBER
2005 CHEVROLET IMPALA
3.4L
V6
2WD
AUTOMATIC
260,000 MILES

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!

Monday, January 9th, 2023 AT 12:16 PM

1 Reply

JACOBANDNICKOLAS

MECHANIC
110,101 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 make bigger)