tranny wont display gears in "M" mode?

[minis7904]

I have a 2006 LBZ, When I shift from drive in to M mode it will not display the gears, and it will not let me shift with the buttons. ANy help would be appericiated. I am geting ready to pull a trailer over the mountains and would like to use this mode if I need to. Thanks..

[DmaxMaverick]

Welcome aboard!

Did it work before? Is the SES (Service Engine Soon) lamp on? Check for codes if it is.

[minis7904]

Yes it did work before, but not all of the time. the SES light is not on, It almost sounds like a wiring problem mabye.. I was able to get it to shift down to 1st when I put the lever all the way down, and the tow mode seems to be working correctly. In drive every thing seems fine.. Any other ideas?

[DmaxMaverick]

Manual shifting is just another operational mode, and can be inhibited if certain conditions aren't met (such as engine/tranny temp ranges). Please describe the statistical data (engine/tranny temps, speed, current gear range, etc.) when you are trying to use it, and how you are activating it. Also list any modifications you've made.

It could be a wiring issue. You can connect a scanner (or a Predator) to view what the PCM is seeing when it's selected. If you select M, and it doesn't change the PCM value, and there are no codes present (some won't immediately trigger the SES), then it could very well be an electrical problem. While it isn't common, there have been some reports of the column harness failing on earlier trucks, preventing T/H mode. Other than the obvious connector clean/check, it may be an issue with the NSBU or the column harness.

[minis7904]

The engine and tranny temps were higher than normal, that is why I was triing to use the manuel shifting. I was pulling a camper at about 65 mph on a fairly flat road. I even stopped and tried putting it in M and it acted just like it is in drive. I have a bully dog programmer. It is the basic model and only has a tow/economy mode which it is on.. I will put it to the stock one tonight and see what happends. No other mods.

I also am wondering about the overheating and the fan clutch, I have read that you should hear it kick on, but I never do. The fan is turning and when i revved up the engine it looked like it went faster. Is it engaged? SHould the fan not be turning when the engine is about 150 deg?

Thanks

[DmaxMaverick]

The fan should always turn when the engine is running. The fan clutch isn't an on/off clutch. It's a viscous coupling, like the torque converter. It should speed up as engine temps increase, and is actually controlled by the thermostats, more than anything else. Although your engine temp may indicate gage movement, if the stats are closed, there is little coolant circulating through the radiator, thus less warmer air passing to the clutch. When it engages, you should be able to hear it, but seldom at idle speeds. If under load, such as accelerating or climbing a grade, the roar can be very loud. If your indicated engine temp increases beyond 210-220°F during a loaded condition and it isn't engaging, something isn't right. The stats aren't opening, the clutch isn't responding (bad clutch or obstructed cooling stack), poor instrumentation (bad sender or gage, meaning it isn't actually that hot), or engine speed is too low to notice it. If it is in fact overheating (or just hotter than the PCM anticipates), it may be preventing some operational modes. In any case, 65 MPH on a level surface shouldn't be causing excessive engine temp, or any abnormal condition, loaded or not.

Definitely remove your power mod and try again. They are a wild card when diagnosing issues, and should always be removed as a first step. If you have a real problem (absent of electronic mods), it's much easier to identify it.

[minis7904]

Thanks ill give that a try and see what I find out tonight.

[minis7904]

The truck runs fine when I am not pulling any thing. Seldom gets over 200 deg. Does that eliminate anything?

[dunny96]

Not sure about the shifter, but my '06 lbz temps have to be around 240 or so to get the fan engaged. It may not be getting hot enough to engage the fan, but you definately can hear it roar when it finally does.