This guide explains when and how to check your Allison transmission fluid, the tools you need, common mistakes to avoid, and recommended maintenance tips.
Check Allison Transmission Fluid Level
Allison transmissions may have a dipstick (manual check) or a digital fluid check through the shift selector. Below are instructions for both.
1. Manual Dipstick Method
This applies to many RVs, trucks, buses, and older commercial vehicles.
Step 1: Warm Up the Transmission
Fluid expands when hot. For an accurate reading:
- Start the vehicle.
- Let the transmission reach operating temperature (160°F–200°F / 71°C–93°C).
- Shift through all gears, pausing briefly in each.
- Leave the vehicle idling in PARK.
Step 2: Park on Level Ground
Uneven ground will give a false low reading.
Step 3: Locate the Transmission Dipstick
It is typically found:
- At the rear of the engine bay
- Labeled “TRANSMISSION”
Some RVs place it near the firewall.
Step 4: Pull Out the Dipstick
- Wipe it clean with a rag.
- Reinsert it fully.
- Pull it out again to check the level.
Related Allison Transmission Fluid Capacity Chart(All Models)
Step 5: Read the Fluid Level
The dipstick will show:
- HOT RUN range (use when at operating temperature)
- COLD or IDLE range (use only for quick checks)
The fluid should be within the HOT FULL range.
Step 6: Inspect Fluid Condition
Healthy Allison transmission fluid is:
- Bright red
- Clean
- Not burnt
- Not foamy
If the fluid is brown, black, milky, or smells burnt, you may need a fluid change or diagnosis.
Step 7: Top Off if Needed
Use the correct ATF, commonly:
- TES 295
- TES 668
- Dexron III (older models)
Add small amounts at a time to avoid overfilling.
Related Transmission Fluid Level Chart(For All Types)
2. Shift Selector Digital Fluid Check (Allison 5 & 6 Speed)
Many modern Allison transmissions allow checking the fluid via the shift pad.
How to Access the Digital Fluid Level:
- Park on level ground.
- Bring the transmission to operating temperature.
- Leave the engine idling in PARK or NEUTRAL.
- Press the following on the shift selector:
“Up” + “Down” buttons simultaneously
or
Press “Diagnostics” twice, depending on the model.
The pad will display:
- “o L o” → fluid OK
- “Lo 1, Lo 2, etc.” → low fluid (number = quarts low)
- “Hi” → overfilled
- “– – –” → fluid not warm enough for a reading
This is the most accurate method for newer transmissions.
Related Automatic Transmission Fluid Color Chart(All Colors)
When to Check Allison Transmission Fluid
Allison recommends checking the fluid:
- At every oil change
- After heavy towing or long-distance driving
- Before long trips
- If you notice unusual shifting behavior
- If the transmission temperature runs hotter than normal
Some Allison transmissions include the Prognostics System, which can automatically monitor fluid levels and conditions. However, manually checking is still crucial, especially for older units.
Signs Your Allison Transmission Fluid Is Low
Watch for these common symptoms:
- Delayed gear engagement
- Hard shifting
- Shuddering at low speeds
- Overheating
- Slip during acceleration
- Transmission fault codes
If any of these appear, check your fluid immediately.
How Often Should You Check Allison Transmission Fluid?
For most vehicles:
- Monthly for personal use
- Weekly for commercial use
- Before and after towing heavy loads
If using TES 295 or TES 668 synthetic fluids, Allison allows extended drain intervals, but fluid checks are still recommended.
Related Aisin Transmission Fluid Compatibility Chart(For All Models)
Tips for Maintaining Healthy Allison Transmission Fluid
- Use only approved Allison fluids
- Keep an eye on transmission temperatures
- Avoid riding the brakes while towing
- Install an auxiliary transmission cooler if needed
- Change fluid and filter at recommended intervals
- Don’t mix fluid types unless approved
Synthetic TES-295 and TES-668 fluids offer significantly longer life and better heat resistance.
Common Mistakes to Avoid
- Checking fluid when cold (gives false low)
- Overfilling the transmission can cause foaming and failure.
- Using the wrong ATF
- Ignoring burnt-smelling or discolored fluid
- Parking on a slope during the check
FAQs
How to check transmission fluid level on Allison?
To check Allison transmission fluid, warm the transmission to operating temperature, park on level ground, leave the engine idling, and use either the dipstick or the digital shift-selector check. Wipe and reinsert the dipstick to read the HOT range, or press the diagnostic buttons on the shift pad to view the fluid level electronically.
Do you check Allison transmission fluid with the engine running?
Yes, Allison transmission fluid must be checked with the engine running. The transmission needs hydraulic pressure for an accurate reading, and the fluid must be at full operating temperature.
What is the proper way to check transmission fluid level?
The proper method is to warm the fluid, park the vehicle on level ground, leave the engine idling, shift through all gears briefly, then check the fluid using the dipstick or the electronic shift pad. Always read the HOT range for accuracy and ensure the fluid is clean and within the recommended level.
Do you check transmission fluid in neutral or park?
For most Allison transmissions, you check the fluid in PARK with the engine idling. Some commercial configurations may allow checking in NEUTRAL, but PARK is the standard and most reliable position.
Is it better to overfill or underfill a transmission?
Neither is good, but overfilling is more dangerous. Too much fluid can cause aeration and foaming, leading to overheating, slipping, and internal damage. If you must choose, slightly low is safer than overfilled, but always correct the level as soon as possible.
What color should Allison transmission fluid be?
Healthy Allison transmission fluid should be bright red and clear. Dark red or brown indicates old fluid, black suggests overheating or burning, and milky fluid means contamination, often from coolant or water.
Final Thoughts
Checking your Allison transmission fluid level is simple but critical for maintaining performance, reliability, and longevity. Whether you have an RV, heavy-duty truck, or commercial vehicle, a quick fluid check can prevent costly repairs and ensure smooth shifting on every drive. Follow the recommended steps, use the right fluid, and stay proactive with your transmission maintenance.
