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Check Trans Light - Won’t shift out of nuetral


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2006 Beaver PT with 6 speed Allison. Only 33,000 miles. My speedometer is racing up and down immediately after I start the engine.  The check trans light is on.  I can move my rig. Motorhome has been stored under cover since Thanksgiving.  The chassis batteries were dead. I charged them and then this issue with check trans occurred. I’ve unplugged the trans sensors and reconnected them. The check trans light went out but came back on. At no time would the transmission go into gear. The speedometer is racing  and the  odometer is racking up 10ths of a mile every few seconds.  I disconnected the old batteries for 36 hours and then installed new batteries.  This did not correct the issue. Please offer suggestions. Thanks 

 

 

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Posted (edited)

You will need to get the diagnostic codes from the transmission / engine to figure out what next to do.

The Allison trans there are buttons to push and the shift console will blink with a code you can look up.

If there is an engine issue, you will need a compatible Scan tool hardware and software to get the Diagnostic Trouble Codes (DTCs)

 

Start there.  You can google how to do the above.

Edited by DavidL
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Posted (edited)

With the ignition on, to get the Allison into Diagnostic mode you push the up and down arrows TWICE. The first code should be displayed. To get to any additional codes you push the mode button each time to get to any those codes.

It is possible that a bad ground wire in your dash is causing the gauge problems.

Edited by Dr4Film
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Posted (edited)

Thank you both. I was able to get two codes. P0722 and P0880.  I’ve goggled both of these.  I’d like to check to connections to the TCM. Any suggestions as to where it would be located? Is on on the transmission? 

I cleared the codes and only P0722 returned 

Edited by jlynn37064
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6 minutes ago, jlynn37064 said:

Thank you both. I was able to get two codes. P0720 and P0880.  I’ve goggled both of these.  I’d like to check to connections to the TCM. Any suggestions as to where it would be located? Is on on the transmission? 

WITH MONACO??.  Have you looked in the Chassis Electrical Section of your manual.  Many have the FRB layout and “mark” the TCM.  It WILL BE UPFRONT.  90% on that. If is often in the FRB or maybe one bay back…in the ceiling …yes..either in or above the ceiling panel.  I just looked at a 2014 Dynasty manual.  Go to the chassis electrical….that gives you a visual….they are close to the same.

You can google Allison MH3000/4000 TCM image.  That’s one way to figure out what you are looking for…looks like

BTW….Call ALLISON TECH SUPPORT….they are good and user friendly…

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772 is output speed sensor, which confirms the obvious at this point.  And 880 is TCM input that seems like it could be the speed sensor, or the power supply voltage low, which you obviously had also, and since this code didn't return I'd ignore it for now.  Since you unplugged the sensors, you're not afraid to get dirty, remove the output sensor and clean it.  If that fails, see if the output is the same as the input speed sensor and swap them.  Also, check the wiring from the output sensor to the main harness for chaffing, cracks, rodent damage, etc. 

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Benjamin, thanks for the suggestion of looking at the input sensor.  It is the same sensor. I swapped them but still receiving the same code. The Check Trans light goes out when I unplugged and reconnect the output sensor.  I can start the engine and select DRIVE and nothing happens. When I select REVERSE the check trans light comes on.  I removed the wiring loom and inspected the wires. I found no visible issues. Someone suggested that the blue ground wire coming off one of the sensors can be an issue.  Are you familiar with this wire? 

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Posted (edited)

I am not familiar with that blue wire.  The only thing I'd have left to check are transmission instrument's troubleshooting directions on their website, which may not apply to your 2006, but worth a check.  And an allison manual which I've found online for the older model allison, the manual has detailed directions for diagnosing based on symptoms, and also wire resistance checks.  There is a ton of info on forums, just hard to find the right question. 

Since it's been a while since it ran, I'd find the transmission "brain" and check it for rodent damage, condensation, loose connections, whatever.  Maybe even warm it up with a hair dryer?

Edited by Benjamin
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Very interesting.  Lots of possible causes, but not that many that would happen in storage.  You're getting this code standing still immediately on start up, and there's only one thing that sets this code (800RPM change in 2 seconds) so the TCM is obviously reading AC frequency, and it's not from the stationary signal wheel, probably not from the sensor (you tried both), it could be an internal TCM failure that's above my pay grade, or any wiring interference would have some AC source.  The main AC source on a vehicle (assuming you've unplugged and turned off inverter and generator) is the alternator.  You mentioned the batteries were dead, could be coincidence or could be leaky diodes that would also cause AC to be present in the DC.  I'd measure the AC at the alternator B+ output, or even disconnect the small wires from the back of the alt, so it's not charging, depending on model.  Not likely, but I don't know what else to try. 

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