Chevy Impala Forums - View Single Post - Neutral safety/gear indicator
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post #6 of (permalink) Old 04-05-2019 Thread Starter
Jaestes
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Quote:
Originally Posted by plano-doug View Post
Quote:
Originally Posted by Jaestes View Post
Any body have any ideas what to look into? I've found the trans range sensor is internal. I did not remove the trans so I'm guessing theres a wiring issue somewhere. Does anyone know where I can find a wiring diagram or any other potentially helpful?
I've attached a drawing I have for the 2008, but I think it should be the same for 2012.

Four wires which indicate the gear shift position go from the transaxle to the transmission control module (TCM). The colors are TN/WH, YE, GY, and WH.

From the TCM, a serial link goes to the instrument cluster. The PRND321 display should reflect what the TCM sees on the four wires above.

A separate, 5th wire goes from the transaxle to the engine control module (ECM). This wire is OG/BK. This signal provides the neutral safety function.

My take is that this is the only signal from the transmission that affects cranking. While the PRND321 display may be blank, all lit up, or on R (for example), the engine should crank if pin W on X100 (at transaxle) is at ~0 volts.

In summary, my take is that the gear selector display issue is separate from the no-crank issue.

Lastly, the other pic attached shows what the four wires from the transmission indicate for the selected gear. The column headings A, B, C and P correspond to pins 29, 46, 23 and 39 respectively at the TCM.

It may be easier to probe these signals at the transaxle connector, X100. There, pins F, G, H and J correspond to A, B, C, and P.

For resolving the no-crank condition, I would start at by probing pin W at the transaxle. It should be low for Park and Neutral, and high for all other positions.

For the PRND321 display issue, probe F, G, H and J, and see if they match the table for all shifter positions.

For the first three rows in the table: For Park, FGHJ should be 0110. If you get 0010, the shifter is between Park and Reverse (if I am interpreting it correctly). For Reverse, FGHJ should be 0011.

HTH.

Doug

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Awesome. You were right. The no crank issue is unrelated. I checked those pins and everything was fine according to the meter
started stripping back the harness and found nothing obvious. Hooked a few things back up, and the gear indicator was functional again. Still no crank. Heres where it gets strange. I pulled the starter really from the fuse box and jumped it to get it to crank. It cranked but my scanner saw no rpm, fuel rail pressure and a few other sensors. The 02 sensors are warm and when you try to start with key, the wipers jump a little. I think I need to pull this harness back out and check everything.
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