2006 Marquis transmission will not shift into 6th gear

[Bill Laatz]

Allison transmission would not obtain 6th gear and Allison shop in Ft. Myers FL said it is a problem in the coach wiring.  They removed the transmission ECM module, checked it (OK), replaced it with their test ECM and still the same.  I drove from Florida to Michigan with the transmission shifting fine 1 to 5 and 5 to 1 but would not shift into 6th gear.  Also, the gear selector will not display fault codes or oil level.  I was going to pull apart all electrical wiring connectors that I can find and clean & lubricate them.  Any other ideas??  63,000 miles

[Bill Lampkin]

Hi Bill! Just another Bill here...On our coach, it'll shift into 6th only if the Economy (!) button on the Allison shiftpad is on (red LED on). Is that how yours works? Maybe try to fiddle with the connector at the back of the shiftpad. Does your Econ button work? Just a thought.

[Steve Huber]

Bill,
Check the connections on the cables that run to the tranny. I had a similar problem (wouldn't shift out of 3rd) and found that it was caused by a faulty connection.

Bill Lamkin, are you sure that your tranny is operating correctly and hasn't been reprogrammed? Having to be in economy mode to get to 6th makes no sense to me. Your C13 has more that enough power to easily cruise in 6th w/o being in economy and lugging the engine by delaying the shift points.
Steve

[Bill Lampkin]

No, not sure about tranny programming, but if I'm starting a climb, I'll take it out of Econ so it will downshift just a bit sooner, and when I reach the top of the hill, and we're over 56 or so, I'll put it back in Econ and it'll shift into 6th. So roadspeed and Econ determine 6th, at least with my ride. We've been yo-yoing up and down the Oregon coast all summer, so not much opportunity to 'let it fly'.

[Eric Maclean Co-Admin]

Bill
The Allison transmissions are set up with 5th and 6th both being overdrives and the 6th gear is set up to be at a speed of above 50 mph before the TCM will allow the shift into 6th.
You may want to browse through the Allison 3000 / 4000 troubleshooting manual to gain some insight into your problem
The manual is located in the coach assist section of the form.

Your problem seems to me to be a communication issue between the TCM and the trans. As was mentioned earlier possibly at the trans connection . It does seem odd that you have no codes with the level sensor not responding.
At any rate the troubleshooting manual will at least help you understand the operation and may even get you on the right track to a repair.

Hope this helps
Eric

[Joel Ashley]

Seems like I’d always take the speed to 62 or so for it to shift up for flat cruising, then could let it drop to 57 before risking it going back to 5th if on Cruise Control and encountering a slight up grade.  Theoretically the factory adjustment was an Allison 5th-6th gear shift point of 56mph or so.  Econo mode involved midrange shifts as I recall, not 5th-6th.

[Keith Moffett Co-Admin]

Since finding the leak in my hydraulic pump I have been focused on the Allison and realized it hasn’t been checked in a long time. 
The instructions say achieve operating temp and then find a flat place to stop, place in neutral and brake on.  Now allow it to idle for several minutes so the ATF drains down to the sump and then simultaneously  press and release both up and down arrows on the key pad.  The shift indicator should flash ‘OL’ (oil level) and ‘OK’.  If fluid is low it should read ‘OL’ ‘LO’ and then the number of quarts low it is.
Mine read ‘6’ on a small slant and ‘5’ when level.  Turned out it was 7 quarts low.
Now not only does it shift up smoothly but also the jake kicks in smoothly .  There is noticeably more power on hills in 6th and where it had shifted to 3rd it now climbs nicely in 5th and 6th.
Might be my imagination but I don’t think so. 
Hope this helps someone here.

[Bill Lampkin]

In our front run electrical bay (1st compartment, drivers side) there is an Allison module, might check the connector there too.