21 rows  Jul 11, 2005  Re: Allison HT740 shift problem: mike miraglia: 9-20-08: We have an oshkosh mixer truck 2001 with a cat c-10 motor, we recently installed another engine (used) and now the tranny won't shift out of first unless it is driven about 5-6 mph. Then it will shift thru the gears ok.

• Ht740 Parts

I have a 1994 Monaco Dynasty. We parked at a resort for a couple of months and started the motorhome to go into town to purchase propane.

Everything went well until I started to put it in gear. All at once the do-not-shift light came on, and the shifting pad blinked a couple of times and then went black. Every time I turn the key on, the N blinks a couple of times and then goes black. Nothing is lit up on the shifter pad, and the do-not-shift light stays on. The tach does not work - sometimes if you rev the engine it will go crazy but does not work right.

Does anyone have ideas that I could check out? Stuck in Oklahoma. William Horn. A330 cf6 training manual. Start by verifying 12.0-14 VDC at the TWO transmission fuses in your chassis fuse box. Like any computer, low voltage due to bad battery, discharged battery, poor or corroded connection, etc can cause some peculiar issues. Next, query your Allison for diagnostic codes using your shift pad. Instructions in your Allison manual or here: Also, a good idea to unplug and securely replug the two gang plugs at the Allision TCM and the shift pad.

Though it does not fit your specific issue, be aware that if the idle speed is too high, the transmission will NOT go into gear. So, high idle speed/idled up speed for warm up is (and should be to protect the drivetrain) an automatic shift inhibit.

The Tack signal comes from the Engine ECM. The TCM and ECM are interconnected ( sharing information).

My first thought, since you did not mention any check engine light, is cabling and connections to and from the modules. You have been setting for some time. There is the possibility the some little critter has or is chewing on the cable harness somewhere.

The other thought, is some oxidation on a connector at the ECM / TCM. My first checks would be the area of the ECM as this is the starting point of the tack signal. The Crank sensor signal should be present at the ECM because the engine is starting OK. There is a double headed sensor in the trans.

That sends signals to the speedometer and cruse circuits only. Not a tack signal What Engine does you coach have? I have some information on the circuits for the Cummins Engine ECM. William, If not said before, Welcome to the Forum. You stated that when you start your engine, your transmission has fault codes. You also said that your tac was not working. I have had a similar thing happening in my coach.

I would start the engine and nothing on the dash would work, but the engine still started. I turned the engine off and turned it back on and every thing worked. I have determined that I need to replace the ignition switch. Some times I have to turn it off and on several times to get every thing to come on. Just thought this may help. I was referring to the check engine code switch that is located below and to the left of the steering column.

This allows you to read any engine ECM codes that have been stored. They are 3 digits long and the yellow light will blink, short pause, Red light will blink, short pause, yellow will blink. After another pause the sequence will repeat if there is only one code present. If there are more codes stored the ECM blink sequence will change. Like 171 pause 171. More than one code. 171 pause 224 pause 331 pause and so on.

Or Yellow, Red Red, Red Red Red Red Red, Yellow. Do the Check engine lights come on when you first turn on the key? I have pictures of the ignition SW assembly used on my unit, but I'm at the limit for the number of pictures I can post unless I do not completely understand how to get more of them up loaded. This is going to be hard to diagnose because the shifter does not stay connected. It could be a problem with power supplied to either the trans ecu or the shifter. Suggest you call Allison service for help how to correctly check for power and ground. The Allison is all electronic and will not work when voltage drops too low less than 10 volt.If you can verify you have the power you can dig further.

Also, I would think there is a diagnostic plug for the Allison somewhere possibly out at the back in a compartment near the trans. Let us know what you find. William I checked with my local Allison service guy in Pennsylvania that I knew. Just a few ideas of his: Can you keep the key pad lit if you turn the key on but do not start the engine. If so you could retrieve codes which would be helpful. Also, he suggested checking the direct power cable and ground. It should be at the chassis batteries.

If these are corroded it will create your problem. The connection can look good but corrosion can be inside the terminal and hard to see. He said sometimes he has to peel the connector apart to see it.

He said this is a common problem. He said the direct power allows the trans to function even if the ignition power is bad.

With a bad ignition power the trans will run but the check engine light comes on. If the direct to battery power is bad it will not power up. Hope this helps.

William, Glad you got some propane delivered. I have been reading over all your posts again. No tack signal present,3060 Allison and 300 Cummins. Got to believe the trans is not shifting because the tack signal is not present on the Gauge.

Ht740 Parts

The Engine starts up with no problem and no engine codes present, so the crank sensor is working and its signal is reaching the engine ECM, this signal also is used to control the fuel injection system. The only thing I can come up with is there is an open wire between the Engine ECM and the TCM. The fact that the Tack signal is missing at the Tachometer is it comes from TCM ( Could be defective) or a connection problem between the ECM and TCM. Hoping my thoughts can help narrow down the area of the issue. Good luck and let us know what you find to fix the problem.

William, Check this link. This could be the problem, if you have a meter and read the voltage at start up with the meter connected to the power circuit,watch the meter and see if the voltage drops and the shift pad then goes blank. The ECM for the transmission is located right in the shift selector area, from what I have been able to dig up so far. This makes some sense to me because it was working fine until you tried to engage the transmission after it had been sitting for a period of time, positive power is supplied through a butt connector ( Red Wire) near the control module. Bad connection no transmission and no Tachometer reading.