A 6.7 Cummins RAM rolls in with the light on and a complaint that it hangs before it grabs second. You pull codes and get P0732 — Gear Ratio Error in 2nd. Then you run the factory 2nd Gear Clutch Test, it passes clean, and you are left wondering whether the code is lying. It is not. P0732 has a trap in it that P0731 does not, and if you miss it you will either condemn a good transmission or hand back a truck that comes right back.
More coverage in our Dodge transmission hub and RAM transmission hub.
What the TCM Is Actually Measuring
The 68RFE runs two speed sensors. The input speed sensor reads 60 teeth off the input clutch hub; the output speed sensor reads 30 teeth off the park gear. Divide input rpm by output rpm and you have the ratio the unit is delivering at that instant. The controller knows what it commanded, so it knows the answer.
Per the ATSG clutch application chart, the 68RFE produces 3.23:1 in first, 1.83:1 in second, 1.41:1 in third, 1.00:1 in fourth, 0.81:1 in fifth, 0.62:1 in sixth and 4.44:1 in reverse. With 2nd commanded the controller expects input speed to run about 1.83 times output speed. The factory set condition is short: the code sets if the ratio of the input rpm to the output rpm does not match the current gear ratio, monitored continuously with the engine running and the transmission in gear, and it can take up to five minutes of problem identification before illuminating the MIL.
One more line from the same chart saves wasted teardowns. Ratio DTCs set only if the transmission slips after first achieving the correct ratio, so a unit with no drive may set no ratio code at all. P0732 is a slip code, not a no-second-gear code. If you have it, the unit made a real 1.83:1 and then lost it.
What Actually Holds Second Gear
Second gear on a 68RFE is a two-clutch job. Per the ATSG application chart, second applies the underdrive (UD) clutch and the second (2C) clutch together. The factory chart confirms it from the other direction: in Step 3 you are told to look in Event Data for DTC P1790 with target gear = 2nd, or with both 2C and UD clutches applying.
P0732 does not tell you which of the two let go. The UD clutch is a single-sided pack in the input clutch housing; the 2C is a separate holding clutch in the 2C/4C retainer. They fail differently, and only one shows up on the scan tool test.
The Trap: The 2nd Gear Clutch Test Cannot Find the 2C Clutch
This is the single most important line in the entire P0732 chart, and it is easy to blow past:
"If the 2C clutch is faulty, the overrunning clutch will hold and the slip test will pass. The 2nd gear clutch test will not detect a faulty 2C clutch. However, it will detect a faulty UD clutch."
The scan tool test named after second gear cannot detect the clutch second gear is named after. With the vehicle held still, the overrunning clutch carries the reaction load, so a burned 2C pack sits there and holds. Input speed stays at zero and the test passes. Nothing is wrong with the test — it is a UD clutch test wearing a second-gear label.
So a passed 2nd Gear Clutch Test means exactly one thing: the underdrive clutch is good. It does not clear the 2C, and the chart does not treat it as if it does. The shared RFE chart states it outright: if the 2C clutch is faulty, the overrunning clutch will hold and the slip test will pass (per the FCA 45RFE/545RFE P0732 diagnostic chart, which the 68RFE chart follows). A pass sends you to the intermittent checks and then to a road test, and the road test is what catches the 2C.
Working the Chart in Order
- Pull every code first. If any transmission solenoid, line pressure, speed sensor or loss of prime DTCs are stored, those come first. If P0944 (loss of prime) is present, it goes to the front of the line before anything else.
- Read and record all Event Data first. If the fault is not present now, that snapshot is your entire diagnosis.
- Check input rpm in Event Data. If it read zero when the code set, the sensor lied, not the clutch. Go diagnose the input speed sensor and wiring as if P0716 were current.
- Check line pressure in Event Data. The chart gives a hard number: is it more than 10 psi below desired line pressure? If yes, drop the pan for debris and inspect the primary oil filter and seal for cracks, plugging or mis-installation. If the filter is clean, pull the pump and check the main regulator valve for sticking, scoring and damage.
- Run the 2nd Gear Clutch Test. Bring throttle angle (TPS Degree) to 30 degrees for no more than a few seconds — do not sit in it, you will cook the unit. Input speed must stay at zero. If it climbs, the UD clutch is slipping and you are going in.
- If it passed, road test. Erase codes and drive it. The question the chart asks is specific: does the transmission fail to make a 1-2 upshift, staying in 1st and then shifting straight to direct gear, or is there obvious slippage in 2nd? That is your 2C signature.
For intermittents, remove the ignition switch feed fuse from the TIPM before wiggle testing — the chart carries a warning on this, because leaving it in allows the truck to be started in gear. Install Transmission Simulator, Miller tool 8333, then wiggle the speed sensor wiring and connectors. Ratio DTCs can also set under temperature extremes, so ask whether it only happens very hot or very cold.
Grey Sludge and the Backwards Reaction Plate
When the road test confirms slippage in 2nd, the chart sends you to the pan, and it tells you exactly what to look for. If grey sludge is present, check for an improperly assembled 2C clutch with the thick reaction plate not against the case.
That is not wear, that is somebody's previous build. Put the thick reaction plate in backwards and the pack has nothing solid to react against, so it hammers itself and grinds the fluid grey. Find that sludge and you know the unit has been apart, and why it came back.
From there, pull the valve body and air check the 2C hydraulic clutch circuit in the 2C/4C clutch retainer. The chart notes the 2C passage contains a small bleed orifice, so a small amount of air leakage is normal — you are looking for excessive leakage, not zero. Check the 2C piston seals and that bleed orifice. If the 2C failed and you cannot point at an obvious cause — cut piston seal, cut tower seal, stuck regulator valve — the chart says replace the transmission solenoid/TRS assembly in addition to the internal repair. An unexplained burned clutch means the apply was wrong, and new frictions behind the same solenoid pack buys you the job back.
If the Circuit Holds Air
Then the leak is upstream. Check the 2C accumulator piston for cracks or a cut seal, check for a cut or missing No. 7 or No. 5 check ball in the main valve body (both are on the factory P0732 cause list), and check the solenoid switch valve and its plugs for sticking or excessive wear in the bore. That last one is the usual suspect on a high-mileage unit — GEARS Magazine reports that worn valve body bores and outer switch valve plugs cause code P0871 roughly 90 percent of the time, and the same wear crossleaks apply oil into adjacent circuits.
68RFE Friction Clutch Module Kit
If the road test showed slippage in 2nd and the pan came out dirty, the frictions are done. The complete friction module for 2007-up 68RFE builds — 2C and UD stacks together.
See the 68RFE friction clutch kit →Need pistons, seals, thrust bearings, solenoid blocks or a full overhaul kit instead? Browse the whole 68RFE parts collection.
Checking the Gearsets Before You Blame the Clutch
If the 2C circuit is tight and the accumulator and check balls are good, the chart checks the geartrain for broken splines through the case windows, with the unit still in the truck.
- Reverse gearset splines. Hold the output shaft with the manual lever in Park, apply the 4C clutch with 30 to 40 psi shop air at the center bulkhead port, and try to rotate the input annulus gear and drive shell. The overrunning clutch means it should only turn one way. If it rotates, check the reverse annulus spline to the input carrier and the reverse sun gear spline to the reaction carrier hub.
- Drive shell weld. Release the output shaft and 4C, apply only the L/R clutch at 30 to 40 psi, and try again. If it turns now, check the drive shell weld to the input annulus gear.
The Pressure Side: What Normal Looks Like
Since the chart hinges on line pressure being within 10 psi of desired, you need to know what healthy looks like. Per GEARS Magazine, a good 68RFE idles at 60 to 70 psi commanded and actual, with line pressure duty cycle at 22 to 24 percent. Anything under 10 percent duty cycle is not suitable for this transmission, and a unit sitting at 5 percent duty cycle with actual pressure below desired means the pump cannot deliver what the controller is asking for. On tuned trucks that is often the tune commanding more than the pump can make.
The pressure switches behave predictably too. GEARS documents the RFE switches as five individual switches, naturally open with no hydraulic pressure, closing at 22 psi and opening at 11 psi. Closed reads 25 to 50 mV at the controller; open reads full system voltage. So when Event Data shows the UD or 2C pressure switch open while line pressure matches desired, that circuit genuinely failed to hold 22 psi. Air check both circuits, and if they are fine, replace the solenoid/TRS assembly.
2024 Trucks: Check the Bulletin Before You Quote a Rebuild
If the truck is a 2024, stop and check the build date. Stellantis TSB 21-012-25 REV. B (February 21, 2025) covers 2024 RAM 2500 and RAM 3500 pickups built on or after June 14, 2024 and on or before September 4, 2024 with the 6.7L Cummins (sales code ETL) and the 68RFE (sales code DG7). The cause is rear selective thrust bearing cracking, and P0732-00 is on the DTC list along with P0729, P0731, P0733, P0734, P0735, P0716, P0218, P0841, P0868, P0871, P0876 and P0944.
The bulletin repair is transmission replacement (part K52109056AC, refilled with ATF+4 to MS-9602-F), then a wiTECH Quick Learn. It was also released as Rapid Service Update 25-018, so applicable VINs are already loaded. Run the VIN first — a warranty transmission beats a customer-pay teardown.
One Note on 2019-and-Later Units
On a 2019-or-newer 68RFE the hardware underneath this diagnosis changed. Per Sonnax, the 2019 update added a lower valve body section with a new reverse accumulator assembly and a new TCC control solenoid, and the solenoid pack connector changed from gray to blue. Because the TCC now has its own solenoid, the low/reverse solenoid only controls L/R apply instead of doing double duty. The pressure regulator lineup was not changed. Mixing a 2019-and-later valve body or solenoid pack onto an earlier case, or the reverse, manufactures ratio and pressure switch codes that have nothing to do with a clutch.
Matching the Fix to the Finding
- Clutch test failed (input speed rose): UD clutch. Air check the UD circuit, check piston seals, reaction shaft support seal rings, the dribbler assembly and pump face flatness.
- Test passed but no 1-2 upshift or slip in 2nd on the road: the 2C side. Pan, grey sludge check, air check the 2C circuit.
- 2C circuit holds air: 2C accumulator piston and seal, No. 7 and No. 5 check balls, solenoid switch valve and plugs.
- Line pressure more than 10 psi below desired: fluid level, primary filter and seal, or a sticking main regulator valve. No clutch work yet.
- Input rpm zero in Event Data: input speed sensor and wiring. Code set in Park, Reverse or Neutral: the powertrain control module. Neither is a teardown.
- Drive shell rotates on the 4C or L/R air check: broken reverse gearset splines or a failed drive shell weld, not a clutch.
- 2024 truck built 06/14/24 to 09/04/24: run the VIN against TSB 21-012-25 and RSU 25-018 first.
After any internal repair, run the Quick Learn so the controller re-adapts pressure and shift timing, then complete the 68RFE transmission verification test before the truck leaves. Refill with Mopar ATF+4, the fluid ATSG lists for this unit, and set the final level at operating temperature. Our 68RFE fluid type and capacity guide has the service and dry-fill numbers.
Need parts for this job?
2C and underdrive frictions, bonded pistons, accumulator kits, seal kits, thrust bearing kits, solenoid blocks and ATF+4 — what a P0732 repair consumes, shipped fast from the USA.
Shop 68RFE parts →FAQ
What does P0732 mean on a 68RFE?
P0732 is Gear Ratio Error in 2nd. The transmission control module divides input shaft speed by output shaft speed and compares that number to the 1.83:1 second gear ratio the 68RFE is supposed to be producing. If the measured ratio does not match while 2nd is commanded, the code sets. The factory chart notes it can take up to five minutes of problem identification before the MIL comes on, so the truck often drives badly for a while before the light appears.
Why does the 2nd Gear Clutch Test pass when the 2C clutch is bad?
Because the overrunning clutch takes the load during the test. The factory chart states it plainly: if the 2C clutch is faulty, the overrunning clutch will hold and the slip test will pass. The 2nd Gear Clutch Test will not detect a faulty 2C clutch, it will only detect a faulty UD clutch. A passed test rules out the underdrive clutch and sends you to the road test, it does not clear the 2C.
What does grey sludge in a 68RFE pan mean with P0732?
The factory chart calls it out specifically: if grey sludge is present, check for an improperly assembled 2C clutch with the thick reaction plate not against the case. That is an assembly error from a previous build, not normal wear. The backwards plate lets the pack chatter and grind itself into the fluid, and no amount of new frictions will fix it if the stack goes back together the same way.
My 2024 Ram set P0732. Is that a known factory problem?
It can be. Stellantis TSB 21-012-25 REV. B covers 2024 Ram 2500 and 3500 trucks built between June 14, 2024 and September 4, 2024 with the 6.7L Cummins and the 68RFE. The cause is rear selective thrust bearing cracking, and P0732-00 is one of the listed DTCs along with P0731, P0733, P0734, P0735, P0729, P0868 and P0944. The bulletin repair is transmission replacement, and it was also released as Rapid Service Update 25-018, so check the VIN before you quote a rebuild.
Does P0732 always mean the transmission has to come out?
No. Three of the Event Data branches in the factory chart end without a teardown. P0732 recorded in Park, Reverse or Neutral points at the powertrain control module. P0732 recorded with input rpm at zero points at the input speed sensor and its wiring. P0732 recorded with line pressure more than 10 psi below desired points at fluid level, the primary filter and seal, or a sticking main regulator valve. Read the Event Data before you pull the truck apart.
Sources
- FCA/Chrysler 45RFE/545RFE service information, P0732 GEAR RATIO ERROR IN 2ND diagnostic chart (2007 Jeep Commander workshop manual, Section 21). The RFE family shares this control logic and chart with the 68RFE. Backs the theory of operation and set condition (input-to-output rpm ratio not matching the current gear ratio, monitored continuously in gear), the five-minute problem-identification delay before the MIL, the 60-tooth input clutch hub and 30-tooth park gear counts, the instruction to address solenoid, line pressure, speed sensor and loss-of-prime DTCs first with P0944 before anything else, the Event Data check for P1790 with target gear 2nd or 2C and UD applying, the zero input rpm branch, the more-than-10 psi below desired line pressure branch with the primary filter and main regulator valve checks, the note that the 2nd gear clutch test will not detect a faulty 2C clutch because the overrunning clutch holds, the 2C and UD bleed orifices, the No. 5 and No. 7 check balls, the reaction carrier to reverse sun gear weld check, and the full cause list. jeep.automotive-manuals.com
- FCA/Mopar 68RFE service information, P0732 GEAR RATIO ERROR IN 2ND diagnostic chart (2009 RAM 3500 HD 6.7L, Section 21). The 68RFE-specific version of the same chart. Backs the RAM-specific steps not in the 45RFE chart: the 30 degree TPS 2nd Gear Clutch Test, the TIPM ignition feed fuse warning and Miller tool 8333 for intermittents, the grey sludge and reversed 2C thick reaction plate check, and the 30 to 40 psi 4C and L/R air checks for the reverse gearset splines and drive shell weld. Available through Stellantis service information (techauthority.com); the public mirror previously linked here is offline.
- ATSG (Automatic Transmission Service Group), Dodge RAM 68RFE technical service information. Backs the clutch application chart showing the underdrive and second (2C) clutches applied together in second gear, the published gear ratios (3.23, 1.83, 1.41, 1.00, 0.81, 0.62 and 4.44 reverse), the description of the 2C and 4C as separate holding clutches with the underdrive and overdrive clutches carried in the input clutch housing, the single low sprag, and Mopar ATF+4 as the specified fluid. atsg.biz
- Stellantis / FCA US Technical Service Bulletin 21-012-25 REV. B, Rear Selective Thrust Washer Failure, February 21, 2025 (via NHTSA). Backs the affected vehicles (2024 RAM 2500 and 3500 built June 14, 2024 through September 4, 2024 with sales codes ETL and DG7), rear selective thrust bearing cracking as the cause, P0732-00 and the full DTC list, transmission replacement part K52109056AC with ATF+4 to MS-9602-F, the wiTECH Quick Learn step, and Rapid Service Update 25-018. static.nhtsa.gov
- GEARS Magazine (ATRA), Fixing the Root Cause of the Problem: Solving Issues with the 68RFE Transmission. Backs the healthy line pressure figures of 60 to 70 psi commanded and actual at idle with line pressure duty cycle at 22 to 24 percent, the statement that anything under 10 percent duty cycle is not suitable for this transmission, and the 5 percent duty cycle with actual below desired failure pattern on tuned trucks. gearsmagazine.com
- GEARS Magazine (ATRA), Dodge RFE Pressure Switch Diagnosis and Code P0871. Backs the five individual pressure switches being naturally open with no hydraulic pressure, closing at 22 psi and opening at 11 psi, the 25 to 50 mV closed signal versus full system voltage when open, and worn valve body bores and outer switch valve plugs causing roughly 90 percent of these codes. gearsmagazine.com
- Sonnax, Chrysler 68RFE 19-Later Changes and Identification, Jim Dial, December 29, 2022. Backs the 2019 hydraulic control changes: the added lower valve body section with a new reverse accumulator assembly and new TCC control solenoid, the solenoid pack connector changing from gray to blue, the low/reverse solenoid losing its TCC duty, and the pressure regulator lineup remaining unchanged. sonnax.com
Shop 68RFE clutch parts →
Related 68RFE guides
- 68RFE P0731: Gear 1 Incorrect Ratio - Causes, Diagnosis, and Fix
- 68RFE P0736: Reverse Incorrect Gear Ratio - Causes, Diagnosis, and Fix
- 68RFE P0871: Pressure Switch Rationality and What It Really Means
- 68RFE Valve Body Problems: Symptoms, How to Test, and Replacement
- 68RFE Rebuild Guide for RAM 2500/3500 Cummins: What Fails and How to Fix It