Allison Transmission Shift Selector Problems

It’s very common to see faulty equipment in RVs since too many variables/companies are involved in production. You’d know this quite well if you own an RV with an Allison Transmission. The company specializes in manufacturing automatic transmissions for medium and heavy-duty vehicles.

Since they mass produce gearboxes, there is always a chance that the quality is compromised or an error develops in the component. For Allison, the issue is in the shift selector. Several users have reported Allison Transmission shift selector problems after years of use. The part fails due to one malfunction or another. In other words, many different things can go wrong, leaving you with no clue how to solve them. It is frustrating for motorhome owners like you, especially when you are just heading out on an adventure.

Here is a list of Allison transmission shift selector problems you can encounter in your RV and some helpful solutions.

Common Allison Transmission Issues & Solutions

1. Transmission Going into Limp Mode

Allison transmissions, especially the 1000 series models, have a limp mode where the transmission restricts to one particular gear – usually 3rd gear – and you can’t go up or down the shifting order. The mode activates if the gearbox goes through some excessive damage or deterioration. The usual suspect, in such cases, is overheating, but you could also trigger the limp mode after pulling heavy loads with your vehicle.

Unfortunately, there is no proper fix for this kind of issue. When your RV’s shift selector gets stuck in third gear, it is time to get the transmission rebuilt. However, you can avoid such a thing by being on top of vehicle maintenance. If you check the transmission fluid regularly and don’t put too much stress on it, you should never experience this problem.

2. Installation Issues

Manufacturing issues aside, sometimes incorrect installation could lead to Allison transmission shift selector problems. When you install the gearbox, you must ensure all complementary parts are also installed and attached properly. Otherwise, the shift selector could develop intermittent or permanent problems. You could employ the services of a technician to ensure everything is in order.

3. TCM Malfunction

The Transmission Control Module (TCM) dictates how the gearbox works. If this component malfunctions, it is highly likely that the shift selector on your Allison transmission also experiences issues. The only fix for this problem is to replace the TCM.

However, such a malfunction is highly unlikely, given the TCM doesn’t experience extreme stress often.

4. Short Wire in the Shift Selector Harness

A short circuit is equivalent to a heart attack in a human being. If it happens within the wire harness that leads to the shift selector, the equipment could go haywire and stop working. You would see this in the form of no power in the shift selector. Also, the display and features would stop working.

Luckily, if it is the first time, you can save the shift selector by replacing the errant wire. You would need the RV’s user manual and preferably a workshop manual to repair the short wire. Once you have taken care of the faulty wire, the shift selector should work fine. However, if it is still not displaying anything, you might have to replace the component with a new one.     

5. Corroded TCM Fuse

The fuse that regulates power to the TCM can be affected by moisture. If your motorhome has been idle for too long and has seen many moisture-laden days, the effect could have transferred to the fuse box. Unfortunately, when the TCM doesn’t receive power, it can’t send commands to the shift selector, and neither component works properly.

Therefore, if you witness an issue in the transmission, you should locate the fuse box inside the battery box. Once you reach the location, check the fuse holder for corrosion. If you can find rust there, clean it with an aerosol cleaner and replace the fuse. Even if the fuse itself is working, you shouldn’t take any chances and replace it while you are there.  

6. Low Supply Voltage

Some users have reported that an insufficient voltage supply to the Allison transmission can cause the shift selector to malfunction. Voltage fluctuation can lead to definite failure and hefty replacement fees.

Luckily, the fix to avoid this malfunction is easy. All you have to do is wire the TCM directly to the chassis batteries, allowing the component to receive sufficient power straight from the source.

7. Power Feed Wire Deterioration

It doesn’t take long for the power feed wire of the shift selector to deteriorate. It rots far quicker than you can imagine, especially in winter. But that only happens if something exposes the wiring underneath the vehicle.

You could have attached the wire harness and not sealed it properly, allowing external elements to damage the wire and let moisture inside. Alternatively, a sharp rock could have chipped away at the wires, exposing them to wetness. Several other possibilities could have compromised the wire housing. So, the first thing you have to ensure is that all the wires and connectors are moisture-proof. This includes asking your mechanic to be diligent when working on your RV.

But how does moisture get inside? Well, you may live in a moisture-laden area. If the humidity is constantly very high, the rotting is also quicker. Moreover, you may have recently driven on icy or water-logged roads. In the winter, the chances of moisture affecting your car are higher; due to the melting ice on the roads. That is when the chances of such a problem considerably increase.       

So, if the shift selector is not working and you have exhausted all other solutions, it is time to look beneath your RV. The chances are high that you find the power feed wire exposed to the environment. In such cases, call your trusted mechanic and ask them to replace and properly stash the wiring to never face this problem again.

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Ever since I was a kid, I've been fascinated by travel. I inherited this passion from my parents. Since my college years and to this day, I have had a passion for traveling in a motorhome. I am here to share my experiences with you.

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