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The Aisin AS68RC is a heavy-duty six-speed behind the 6.7 Cummins in the bigger Ram trucks. It is a tough transmission built for weight, but it is also famous for two things: dropping into limp mode when it gets hot pulling a load, and being sensitive to its own software. When the TCM sees something it does not trust, it locks the trans into a fixed gear (usually a middle gear) and lights the wrench or the check-engine light. No upshifts, no downshifts, harsh engagement, and a truck that suddenly feels like it is dragging an anchor.
Before anyone quotes you a rebuild, understand this: a large share of AS68RC limp events are software, sensor, or heat-related, not a burned-up gearset. The single most-overlooked fix on early trucks is a TCM software update. Overheating from towing, a failing speed sensor, or a solenoid pack fault account for most of the rest. Diagnose in order and you will usually spend hundreds, not thousands.
What Puts an AS68RC in Limp Mode
Limp mode is the TCM protecting the transmission. These are the causes we see most, roughly in order of frequency.
1. TCM Software / Calibration (Check This First on Early Trucks)
The 2007.5-2012 trucks shipped with early calibrations that were overly aggressive about tripping failsafe and had shift-quality issues. Ram released updated TCM software that fixed a lot of nuisance limp events. If your truck has never had the latest calibration flashed, a dealer or a shop with the software can do it before you spend a dime on hardware. This is the cheapest possible fix and it is skipped constantly.
2. Overheating From Towing
The AS68RC makes a lot of heat under a heavy load, especially towing in the mountains in tow/haul off, or with an undersized cooler. When fluid temperature climbs past the TCM's threshold, it drops into limp to protect the clutches. If your truck only limps when you are working it hard and towing heavy, heat is the prime suspect. A larger auxiliary cooler and a temperature gauge are the real fix.
3. Speed Sensors (Input / Output)
The TCM calculates gear ratio from input and output speed. A dropout or erratic signal from either sensor makes the ratio calculation impossible and the TCM immediately protects the trans. Speed-sensor faults are cheap and are a common cause of a truck that limps intermittently but otherwise drives fine.
4. Solenoid Pack
The AS68RC runs its shifts through an internal solenoid pack. Electrical faults, drift, or contamination in the pack cause commanded-vs-actual pressure mismatches and trip failsafe. A failing solenoid pack is one of the more common hardware causes on higher-mileage trucks.
5. Valve Body Wear
High-mileage, hard-towed trucks wear the valve body. Worn bores bleed pressure, the TCM overcompensates, and pressure feedback eventually goes out of range. This usually shows up with a flare or harsh shift before the truck starts flat-out limping.
6. Worn Clutches / Internal Damage
The expensive end. If the fluid is burnt and dark, clutch material is circulating and the internal friction elements are worn. At that point limp mode is a symptom of real mechanical damage and the trans needs a rebuild.
Diagnosis: Codes and the Reset Procedure
Start with a scan tool that reads Chrysler/Ram transmission PIDs and, ideally, live fluid temperature and input/output speed. A generic reader will only show you the P0700 placeholder. You want the specific codes stored behind it.
| Code | What It Means | Where to Look |
|---|---|---|
| P0700 | Transmission control system fault (informational) | Read the specific codes stored behind it |
| P0868 | Transmission line pressure low | Fluid level, pump, valve body, solenoid pack |
| P0731-P0736 | Gear ratio incorrect (1st through 6th) | Speed sensors, solenoid pack, clutch wear |
| P0715 / P0720 | Input / output speed sensor circuit | Speed sensor, wiring, connector |
| P0218 | Transmission over-temperature | Cooler, fluid, towing heat |
| P0748 / P0778 | Pressure control solenoid electrical | Solenoid pack, internal wiring |
How to Reset Limp Mode
To clear the failsafe: key off, then clear the stored codes with a scan tool (or disconnect the battery for several minutes on trucks that allow it). Cycle the key and let the TCM relearn. On many of these trucks a shift-adaptation relearn helps after clutch or solenoid work. Important: a reset only clears the flag. If the fault is still present, the truck will trip right back into limp. Use the reset to confirm which code returns first, not as the repair itself.
Check first, in this order: fluid level and condition (hot, per the Ram procedure, using ATF+4), then scan and record every code with freeze-frame, then confirm whether the truck only limps under towing heat, then check speed sensors and solenoid pack. Confirm the TCM calibration is current before condemning hardware on an early truck.
Bidirectional scan tools
What Each Fix Costs in 2026
Real US ballpark ranges. DIY numbers are parts only; shop numbers include labor at typical independent diesel/transmission-shop rates. Note how wide the spread is: a calibration or a sensor is a cheap day, a rebuild is a mortgage payment.
| Repair | DIY Parts | Shop (Parts + Labor) |
|---|---|---|
| TCM software update / flash | — | $0 - $200 (often covered / minimal) |
| Input or output speed sensor | $40 - $110 each | $200 - $400 |
| Auxiliary cooler + temp gauge (heat fix) | $150 - $400 | $400 - $750 |
| Solenoid pack | $250 - $550 | $700 - $1,300 |
| Valve body (reman) | $500 - $1,000 | $1,200 - $2,200 |
| Fluid + filter service (ATF+4) | $120 - $220 | $300 - $500 |
| Full rebuild (burnt clutches) | — | $3,500 - $6,500 |
The AS68RC is expensive to rebuild, which is exactly why the diagnosis order matters. Rule out the free flash and the cheap sensors before anyone opens the case.
DIY vs Shop — Where to Draw the Line
Do it yourself if the code points at a speed sensor, the truck only limps from towing heat (cooler and gauge upgrade), or you are doing a fluid and filter service. These are all reasonable driveway jobs if you are comfortable under a heavy truck. The AS68RC holds a large volume of ATF+4, so have plenty on hand and check the level by the hot procedure. Do not substitute a non ATF+4 fluid; this transmission is specific about it.
Take it to a shop if you need the TCM flashed (dealer or shop software required), the fluid is burnt, you have ratio-error codes across multiple gears, or valve body pressure codes with a shudder. Those point at internal wear that needs the trans on a bench, and a shop with the right scan tool can confirm a solenoid pack or valve body diagnosis before parts go in.
Parts and fluid you will likely want for the common fixes:
AS68RC solenoid pack
ATF+4 transmission fluid
Auxiliary transmission cooler
Need Parts? Ships Same-Day
Once you have the diagnosis, our companion shop gearboxinsider.com stocks AS68RC solenoid packs, speed sensors, filters, coolers, and full rebuild kits for the 6.7 Cummins Ram. Same-day ship before 2pm Eastern.
Shop Gearbox Insider →FAQ
Why does my AS68RC only go into limp mode when I am towing?
That is the classic heat signature. The AS68RC makes serious heat under a heavy load, and when fluid temperature climbs past the TCM's threshold, it drops into failsafe to protect the clutches. If the truck is fine unloaded but limps pulling a trailer up a grade, the fix is cooling: a larger auxiliary cooler, fresh ATF+4, and a temperature gauge so you can watch it. Chasing solenoids on a heat-only limp is a waste of money.
Can a software update really fix limp mode?
On the early 2007.5-2012 trucks, yes, often. Those calibrations were prone to nuisance failsafe events and Ram issued updates that resolved a lot of them. If your truck has never been flashed with the current calibration, get that done before buying hardware. It will not fix a truck with burnt fluid, but it fixes a surprising number of "randomly limps" complaints.
Is it safe to drive an AS68RC in limp mode?
Short, slow trips to get home or to a shop are fine, since limp mode exists to protect the transmission. But do not tow or run it hard while it is limping. It is locked in one gear with no converter lockup, which makes even more heat, and heat is what damages these units. Get it off the trailer and diagnosed before you load it again.