68RFE Won't Shift Into Overdrive: Strategy, Limp Mode or a Real Failure

"It won't go into overdrive" is one of the vaguest complaints a 68RFE truck comes in with, and it covers four different problems. Sometimes the truck is doing exactly what it was programmed to do. Sometimes it is sitting in limp mode in 4th. Sometimes the TCM has locked out 5th and 6th because of a pressure switch code. And sometimes the overdrive clutch is burnt and the truck physically cannot hold the gear. Each one has a different fix, and the expensive mistake is treating all four like the last one.

This is how I sort it out on the 68RFE behind the 6.7L Cummins in 2007.5-and-later Ram 2500 and 3500 trucks. The clutch logic and limp-in behavior come from ATSG. The shift strategy comes from Ram's own owner's manual. The failure data comes from GEARS magazine and Sonnax. The full list is at the bottom.

Recommended 68RFE parts

The parts that fix a 68RFE that will not go into overdrive: a solenoid and pressure switch block for a failed OD switch or solenoid, a valve body for worn switch valve bores, and a thermal bypass valve for a truck that runs too hot to allow 5th and 6th. Ships from the USA, secure checkout.

68RFE Shift Solenoid Block Pack, Gray Connector 2010-2018

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68RFE Valve Body 2011-2018

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68RFE Thermal Bypass Valve for 2013-2018 Ram 6.7L Cummins

$109.99View part

What "Overdrive" Means on a 68RFE

Per ATSG, the 68RFE has three underdrive gears, a direct 4th and two overdrive gears. 5th is 0.81:1 and 6th is 0.62:1. 4th is 1.00:1. The unit applies two clutches in every range, and the overdrive (OD) clutch is one of the pair in 4th, 5th and 6th:

Two things fall out of that table. First, ATSG says the shift into 5th and 6th only happens after the transmission has completed the shift into 4th. If the truck never gets a clean 3-4, it will never see 5th. Second, the OD clutch carries 4th as well. A truck that tops out in 3rd, or flares badly into 4th, can have the same OD circuit problem as a truck that will not take 5th. Before you do anything else, find out what the truck is actually doing. Watch the gear display in the cluster or log commanded gear on a scan tool.

Step 1: Rule Out What the Truck Is Supposed to Do

A lot of "no overdrive" complaints are shift strategy, not a failure. Check these before you open a code reader.

ERS gear limit

Ram's Electronic Range Select lets the driver cap the highest gear. Per the owner's manual, tapping GEAR "-" turns on ERS, shows the current gear in the cluster and sets it as the top available gear. If the cluster shows a 4 or a 5, the truck will not shift above that gear. It exits only when you push and hold GEAR "+" until the gear limit display goes away. Drivers bump that switch without knowing it, and trucks come off a towing trip with ERS still set.

Tow/Haul mode

The owner's manual says that in Tow/Haul upshifts are delayed, and the transmission downshifts on its own for engine braking when you close the throttle or brake steadily. Loaded, on rolling terrain, the truck can hold 4th or 5th far longer than the driver expects. Turn Tow/Haul off and road test again.

Fluid temperature, cold and hot

ATSG says upshifts into 5th and 6th are delayed when fluid temperature is below 40 F (4.5 C) or above 240 F (115 C). Ram's owner's manual backs up the cold side: on the 68RFE the top overdrive gear is inhibited until the fluid is warm. In extreme cold, at -16 F (-27 C) or below, operation may briefly be limited to first and direct gears only. So a truck that will not take 6th for the first few miles on a winter morning is normal.

The hot side matters more. The manual says that when transmission temperature goes past normal limits, the controller changes the shift schedule and widens the range of torque converter clutch engagement. If it gets close to overheating, the Transmission Temperature Warning Light may come on and the transmission may operate differently until it cools. A truck that loses 5th and 6th after 20 minutes of towing needs a trans temp reading, not a valve body. Log the transmission temperature PID on the road test. If it is running over 240 F, look at the cooler, the cooler lines and the thermal bypass valve. A bypass that stays open sends hot fluid around the cooler instead of through it.

Big tires and tuning

GEARS points to oversized tires and aggressive tuning as root causes of heat and pressure problems on this unit. They load the transmission harder at every road speed. If the truck has a lift and much taller tires on stock axle gearing, expect it to run hot and hold lower gears. GEARS is blunt about it: regearing is the only real fix for that root cause.

Step 2: Stuck in 4th Is Limp Mode

If the truck starts out in 4th and stays there, the TCM has not decided against overdrive. It has shut the transmission down. Per ATSG, when the TCM sees a DTC that could damage the transmission, it cuts the ground to the transmission control relay and all power to the transmission goes off. The hydraulics are designed to give Park, Reverse, Neutral and 4th in Drive without any electronics. Moving the lever to 2 or L gives 2nd. ATSG notes that trucks with ERS do not get the 2nd gear limp-in, because that shifter has no 2 or 1 position.

The fix for limp mode is whatever set the code. Pull the codes before you do anything else. Clearing them and road testing only tells you how long it takes to set again.

Step 3: Read the Codes That Lock Out Overdrive

These are the codes I see most often on a truck that will not go into overdrive:

• P0871, OD pressure switch rationality. The TCM does not see the OD pressure switch in the state it expects for the gear. This is the most common one on this complaint.
• P0735 (gear 5 incorrect ratio) and P0729 (gear 6 incorrect ratio). The TCM commanded the gear and input over output speed did not match. That is a clutch slipping or not applying.
• P0734 (gear 4 incorrect ratio). With OD applied in 4th, this is often the same problem showing up one gear earlier.
• Other pressure switch codes (P0841, P0868) and solenoid circuit codes. These point at a hydraulic or electrical fault in the solenoid block and valve body.

How the pressure switches work

ATSG describes five pressure switches in the solenoid block, one each for the L/R, 2C, 4C, UD and OD circuits. They close at 23 psi and open at 11 psi. They only tell the TCM whether pressure exists, not how much. The TCM checks each switch against the gear it has commanded. If it commands 5th and the OD switch stays open, or the switch closes in a gear where OD should be off, it sets the code and protects the unit.

GEARS gives the electrical values you should see: 12.6 to 14.4 volts with a switch open and 25 to 50 millivolts with it closed. Each circuit runs through a 300-ohm resistor that limits current to 50 mA. Their quick check is a key-on, engine-running test in Reverse, where all five switches should read open. If the OD switch shows closed in Reverse, you have an electrical fault or a stuck switch. If all five read open in Reverse but OD misbehaves in the forward gears, the problem is on the hydraulic side.

Step 4: Find the Hydraulic Cause

Solenoid switch valve bore wear

This is the big one. GEARS reports that worn valve body bores and outer switch valve plugs cause P0871 about 90 percent of the time, from erosion and porosity in the aluminum casting. It is common enough that many shops ream and oversize the solenoid switch valve on every build. Sonnax adds that a worn switch valve bore cross-leaks OD apply oil. When it does, the OD pressure switch sees pressure it should not see, or misses pressure it should. A new solenoid block will not fix a worn bore. Vacuum test the switch valve bore. If it fails, ream it and fit an oversized valve and plug.

Check balls in the wrong places

If the truck was just rebuilt or had a valve body installed and now will not go into overdrive, count the check balls. GEARS lists the mistakes: a No. 6 check ball installed in a five-ball valve body, a No. 6 ball left out of a seven-ball valve body (which gives Neutral in 4th), or a missing No. 4 ball (which brings the TCC on in Drive). A truck that falls into neutral on the 3-4 will never reach 5th.

Line pressure

Log line pressure duty cycle at idle in Drive. GEARS says anything under 10 percent is not suitable for this transmission and a healthy unit shows 18 percent or higher. High commanded pressure at low engine rpm drives the duty cycle down, throws the pressure regulator out of balance and cuts cooler flow. Less cooler flow means hotter fluid, and above 240 F you are back to losing 5th and 6th.

Step 5: When the OD Clutch Is Burnt

If the codes are ratio codes and the scan data shows 4th, 5th and 6th slipping, the OD pack is gone. Sonnax calls OD clutch failure one of the top complaints on this unit. The OE OD steels are only 0.034 in. thick, and the OE OD housing is unsupported at the top and flexes under apply, which heats the frictions early. New frictions will fail the same way if you do not fix the reason the pack burned: the switch valve bore, the pressure and the housing. On a truck that tows or makes extra power, the usual permanent fix is a housing that holds a taller pack with thicker steels. Our 68RFE slipping guide covers the clutch chart diagnosis in detail.

Whatever you repair, finish with a fast learn. Per ATSG, the TCM adapts clutch apply through the clutch volume index as the frictions wear. Sonnax calls a fast learn mandatory after any RFE repair.

Quick Diagnostic Order

1. Look at the cluster. Is an ERS gear limit showing? Is Tow/Haul on?
2. Check fluid level hot and log trans temperature. Is it under 40 F or over 240 F?
3. Stuck in 4th from a stop? That is limp mode. Pull the codes.
4. P0871 or another pressure switch code: do the key-on, engine-running Reverse test, then vacuum test the switch valve bore.
5. Ratio codes in 4th, 5th and 6th: the OD clutch is slipping. Fix the cause, then the pack.
6. After any repair, run a fast learn.

Related guides

• 68RFE P0871 OD Pressure Switch Fix
• 68RFE Slipping: Causes and Fix
• 68RFE Shift Solenoid Symptoms
• 68RFE Valve Body Wear and Fix
• 68RFE Fluid Type and Capacity

FAQ

Why won't my 68RFE shift into 5th or 6th gear?

Start with the simple causes: an ERS gear limit showing in the cluster, Tow/Haul mode delaying upshifts, or fluid below 40 F or above 240 F, where ATSG says the 5th and 6th upshifts are delayed. If none of those apply, pull codes. An overdrive pressure switch code such as P0871, a ratio code, or limp mode points to the OD hydraulic circuit or clutch.

Why is my 68RFE stuck in 4th gear?

Stuck in 4th with the lever in Drive is the 68RFE's limp-in mode. Per ATSG, when the TCM sees a fault that could damage the transmission it cuts power to the transmission control relay, and the hydraulics default to 4th. Read the stored codes, because the code tells you what to chase.

Does Tow/Haul mode stop the 68RFE from shifting into overdrive?

It does not lock out 5th and 6th, but Ram's owner's manual says upshifts are delayed in Tow/Haul, so the truck holds lower gears longer, especially loaded or on grades. Turn Tow/Haul off and road test again before diagnosing anything.

What causes code P0871 on a 68RFE?

P0871 is the overdrive pressure switch rationality code. GEARS magazine reports that worn valve body bores and solenoid switch valve plugs cause it about 90 percent of the time, which is why many shops ream and oversize the switch valve on every build. Wiring and the solenoid pack come after that.

Can a cold transmission keep a 68RFE out of 6th gear?

Yes. Ram's owner's manual says the 68RFE's top overdrive gear is inhibited until the fluid warms up, and ATSG puts the 5th and 6th delay below 40 F (4.5 C). On a cold morning the truck may not see 6th until it has been driven for a while. That is normal.