P0730 is arithmetic, not a diagnosis. The PCM knows how fast the turbine shaft is turning and how fast the output shaft is turning. It divides one by the other, compares the answer against the ratio it expects for the gear it just commanded, and if the answer sits outside the window long enough, it stores a code. That is the entire test. The code does not know whether a band slipped, a planetary is the wrong ratio, or a valve bore leaked away the pressure that was supposed to hold something still.
On a 5R55W there are four realistic answers, and they are not equally likely. Working them in the wrong order is how shops end up buying the same repair twice.
The Ratios the PCM Is Checking Against
You cannot evaluate a ratio code without the ratio table, and a lot of what circulates online for this unit is wrong. Wayne Colonna, president of ATSG, published the numbers straight out of Ford's 5R55 W/S & N Transmissions Theory and Operation manual:
- 5R55W: 1st 3.22, 2nd 2.41, 3rd 1.54, 4th 1.00, 5th 0.75
- 5R55S: 1st 3.22, 2nd 2.29, 3rd 1.54, 4th 1.00, 5th 0.71
- 5R55N: 1st 3.22, 2nd 2.41 early or 2.29 later, 3rd 1.54, 4th 1.00, 5th 0.75 early or 0.71 later
Look at where the W and the S differ: only second and fifth. That is not a coincidence, and understanding why is the key to the whole code. The overdrive planetary in these units runs 1:1 from the input shaft to the center shaft until the overdrive band applies and holds the sun gear. When it applies, the input shaft turns slower than the center shaft and the set overdrives. The overdrive band is applied in second and in fifth. So second and fifth are the two gears whose ratios are set by the overdrive planet, and they are the two gears that move when anything in that circuit is wrong.
Doing the Math on the Scan Tool
Graph TSS (turbine shaft speed) and OSS (output shaft speed) together with commanded gear and TFT, then road test through all five gears at light steady throttle. Ratio is simply TSS divided by OSS.
Pick a convenient output speed and the expected turbine speeds fall out. At 1,600 rpm on the output shaft, a healthy 5R55W should show roughly 5,150 rpm turbine in first, 3,860 in second, 2,460 in third, 1,600 in fourth, and 1,200 in fifth. Note that last one: in fifth the turbine turns slower than the output shaft. Techs who have not watched an overdrive unit on a graph sometimes see that and assume the sensor is lying.
What you are hunting for is which gear misses. A ratio that reads high in one gear means something that should be holding is slipping. A ratio that is stable but wrong by a consistent small percentage in second and fifth only, with nothing slipping, is a completely different problem, and it is the one nobody expects.
Cause 1: The Wrong Overdrive Planetary Is In It
This is the cause that gets missed, because it shows up on a freshly rebuilt unit with new parts in it. There are two overdrive planetary assemblies for this family, and per Colonna they are:
- Set 1: overdrive ring gear 94 teeth, overdrive sun gear 38 teeth, pinion carrier 28. Ratio is 94 / (94 + 38) = 0.71
- Set 2: overdrive ring gear 72 teeth, overdrive sun gear 24 teeth, pinion carrier 25. Ratio is 72 / (72 + 24) = 0.75
Sonnax describes the same split in hardware terms: the W uses the 24-tooth overdrive sun gear, the S uses the 38-tooth. Install the wrong assembly and second and fifth are off by roughly five percent, permanently. Colonna reports that the Lincoln LS strategy is especially sensitive to ratio variation, and that 2004 and later applications in general run a tighter ratio tolerance window than earlier ones. That explains the field pattern: an early Explorer with a mismatched planet may only ever get a bumpy 1-2 shift that worsens as it heats up, while a later unit with the identical mistake sets gear ratio codes such as P0732 and P0735 and shifts harshly.
The clean way to confirm it costs almost nothing. Call the dealer with the VIN and order the washer/adapter that splines onto the overdrive sun gear and locks it to the coast clutch drum, basic part number 7660. If the correct washer for that VIN fits the sun gear in the unit, the planet is right. If it does not, you have your answer and you did not have to guess.
Cause 2: Servo Pin Bore Wear
This is the most common mechanical cause by a wide margin. ATSG's Pete Luban, writing in Transmission Digest, calls servo pin bore wear the number one problem behind both the gear ratio error codes and the pressure control solenoid performance codes on the 5R55N, W and S, and says these units are notorious for severely wearing those bores, sometimes at relatively low mileage.
Sonnax documents the mechanism precisely. Servo apply oil is fed through the center of the case bridge and into the servo pin, acting on the cover side of the piston. As the pin bore in the case wears, that apply oil leaks into the barrel area of the case, which hurts shift timing and servo and band apply pressure. As wear progresses, release oil cross leaks into the apply circuits and exhausts at the shift valves. In reverse, both servos are charged from the release side, so a worn pin bore also produces delayed reverse. Sonnax's listed symptoms for the repair sleeve read like a P0730 work order: 1-2, 2-3 and 4-5 flares, gear loss, band lining failure, loss of overdrive and intermediate servo control, and codes 732, 733 and 735.
There is a second-order effect worth knowing. Sonnax notes these units are prone to foaming the fluid in the sump from excess exhaust and valve body wear, which results in fluid out the vent and improper fill indications. Chase a ratio code on a unit that is quietly blowing fluid out the breather and you will fight a level reading you cannot trust the whole time.
After the air test, the band adjustment has to go back to spec, and the back-off differs by unit. ATRA Technical Bulletin 1151 lists 2 turns on both the overdrive and intermediate bands for the 5R55N and 5R55W (and 1999-2002 5R55S), but 1-1/2 turns on both bands for 2003-up 5R55S units. The 2013 ATRA seminar notes on this unit explain why the bands matter so much for ratio codes: 2nd is the forward clutch plus the overdrive band, and the 2-3 shift releases the overdrive band while applying the intermediate band, so any lost apply pressure at either servo shows up as a 2nd, 3rd or 5th ratio fault. Our 5R55S slipping guide maps every gear to the band or clutch that holds it.
The test Luban gives is the one to use: back the band adjustment stud way off so there is no tension on the band, make sure there is oil in the release side of the servo bore, then air apply the servo and watch what blows out of the servo pin bore area of the case. It is not subtle when it is bad. Because the case is what wore, the repair is a wear-resistant aluminum sleeve installed with a reamer that pilots off the pin bore centerline rather than the servo piston bore, which is what lets you salvage a case instead of buying one.
Cause 3: VFS Modulator Bore Wear in the Valve Body
Sonnax's Bob Warnke makes a point that saves a lot of wasted parts: on a 5R55W/S valve body, the TCC modulator bore and the main regulator bore wear first because they are the most active, and as cycle rate climbs, the VFS 1, 2 and 3 modulator bores wear, reducing clutch and servo pressure. Adaptive strategy hides it for a while. After excess wear, gear ratio codes or slippage appear. His warning is direct: the solenoid or the servo pin bore often gets blamed when the real problem is that the VFS modulator valves cannot supply enough pressure.
This ties straight to the electrical codes that ride along with P0730. Luban's chart maps each pressure control solenoid to the gears it feeds. If pressure control solenoid B develops a fault you should see P0775 along with P0732 and P0735, because B is responsible for second and fifth. P0745 points at solenoid A, P0975 at solenoid C. Two rules come out of that experience, and they are worth memorizing:
- You can have a gear ratio code with no electrical solenoid code.
- You are unlikely to have an electrical solenoid code with no gear ratio code.
So address the ratio codes first. ATSG's help line experience is that they have yet to find a case where P0775, P0745 or P0975 was actually electrically generated. These are performance codes wearing an electrical name, which is exactly why a new solenoid pack so often does not fix them.
Sonnax oversized VFS modulator control valve kit 56947J-19K → or browse all 5R55W parts
Cause 4: A Servo Piston That Passes an Air Check
Mike Brown, writing in ATRA's GEARS, documents a failure that will beat a normal bench test. The servo piston goes hard, tears a seal, or delaminates, and release oil leaks across to the apply side. The band then engages when it is supposed to stay off. The complaints are wrong gear starts, bindups in reverse and manual low, and a band or clutch that fails again in short order, usually with gear ratio codes stored.
His caution is the part worth writing on the wall: these servos can pass an air check, because the apply side of the piston is not the problem, the release side is. His in-vehicle check is to raise the vehicle with the engine running in gear and try to turn both band adjustment screws. If they are tight when that band should be released, suspect the servo.
The Order That Actually Works
- Read all the codes and note the pattern. P0732 with P0735 points at the overdrive circuit, whether that is solenoid B pressure, the overdrive servo, or the wrong overdrive planet. Ratio codes spread across unrelated gears point at line pressure or fluid.
- Check fluid level and condition properly, hot. A unit that foams and vents will hand you a false level. Confirm the level is real before you trust anything downstream of it.
- Graph TSS and OSS through all five gears. A ratio that is off by a consistent small percentage only in second and fifth, with no slip, is a hardware ratio problem, not a pressure problem. Go to the planetary.
- Air test the servo pin bores with the band adjustment stud backed off. This is fast, free, and it is the most likely single answer.
- Vacuum or wet air test the valve body, paying attention to the VFS modulator bores and the main regulator bore. Sonnax's 5R55W/S vacuum test guide gives the test points and the part number for each location.
- Only then consider the solenoid assembly. If you do replace it, note Warnke's warning that the base plate and filter are the critical pieces and are not interchangeable between the N and the W/S. Mixing them costs reverse, TCC apply and solenoid oil pressure.
Fluid, Fill and the Relearn You Cannot Skip
Fill spec is MERCON V, Motorcraft part number XT-5-QM. There is real history behind being fussy about it. Warnke documents that the factory fill in the 5R55E, W, S and N prior to May 2005 was an early MERCON V that degraded and took solenoids with it. Ford's interim answer was additive package 4L2Z-19B546-AB under bulletin FSA 04B22, and the final resolution was a revised MERCON V. If traces of the questionable fluid are left behind during a service, the service life of the next solenoid is shortened. If you install a replacement solenoid assembly, prime it: the VFS solenoids ship wet but the lubricant drains off in handling, so fill the circuits with fresh MERCON V and pull fluid through with vacuum before it goes in.
Then relearn it. Ford units built after 2002 use adaptive strategy, so the PCM has spent months compensating for whatever was wrong. Colonna's published procedure is the one to follow:
- Erase keep alive memory with the scan tool and confirm the fluid level is correct.
- Monitor the TFT PID and warm the fluid to 54 C / 130 F.
- Perform five engagements each, five seconds apart, for Park to Reverse, Drive to Reverse, Reverse to Drive, and Neutral to Drive.
- In D or D5, moderately accelerate from a stop to 50 mph so the unit reaches fifth, and hold speed and throttle steady for at least 15 seconds.
- Still in fifth at steady speed and throttle, lightly apply and release the brake to operate the stop lamps, then hold steady another 5 seconds.
- Brake to a stop, remain stopped at least 20 seconds, and repeat the drive portion at least five times.
One useful diagnostic falls out of that procedure. If the shifts are clean at initial start up and get progressively harsher as the vehicle is driven, and you already know the servos and valve body have been addressed and the overdrive planetary was replaced, you are looking at the wrong overdrive ratio set.
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Shop 5R55 parts →Why This Unit Keeps Showing Up
The 5R55W went into Explorers and Mountaineers for 2002 and 2003 before the S took over in 2004 and 2005, and there are a lot of them still on the road. NHTSA's public complaint database for the 2003 Explorer alone holds 1,313 owner complaints, 356 of them filed under the Power Train category. That is not a verdict on the transmission, but it does tell you how much of this work is out there and why the diagnostic order matters. Servo pin bore wear is repairable with a sleeve rather than a case, valve bores are repairable with oversized valves, and a mismatched planetary is a parts problem rather than a rebuild problem. Almost none of the real causes of P0730 on this unit are fixed by the part most people replace first.
FAQ
What are the actual gear ratios in a 5R55W?
Ford's 5R55 W/S and N Theory and Operation manual lists the 5R55W as 3.22 in first, 2.41 in second, 1.54 in third, 1.00 in fourth and 0.75 in fifth. The 5R55S shares first, third and fourth but runs 2.29 in second and 0.71 in fifth. The difference lives entirely in the overdrive planetary, which is why second and fifth are the two gears that change between the W and the S.
Is P0730 different from P0731 through P0736?
Yes. P0731 through P0736 each name one specific gear, from first through fifth plus reverse. P0730 is the general incorrect ratio code the PCM stores when the measured ratio is out of range but the fault does not pin cleanly to one gear, or when the unit never reached the commanded gear at all. Treat P0730 as the same class of failure as the numbered ratio codes, and read whatever else is stored alongside it, because the companion codes are what tell you which circuit to chase.
Can a rebuilt 5R55W set gear ratio codes with new parts in it?
It can, and the usual reason is the wrong overdrive planetary. There are two sets: a 94-tooth ring with a 38-tooth sun that produces 0.71, and a 72-tooth ring with a 24-tooth sun that produces 0.75. Install the wrong one and second and fifth are off by roughly five percent. ATSG reports that 2004 and later strategies have a tighter ratio window, so the same mismatch that goes unnoticed on an early Explorer sets ratio codes and harsh shifts on a later one.
What is the most common mechanical cause of gear ratio codes on a 5R55W?
Servo pin bore wear in the case. ATSG names it as the number one cause of both the gear ratio codes and the pressure control solenoid performance codes on the 5R55N, W and S. Sonnax explains the mechanism: servo apply oil is fed through the center of the case bridge into the servo pin, and as the bore wears that apply oil leaks into the barrel area of the case, hurting shift timing and band apply pressure. As wear increases, release oil cross leaks into the apply circuits and exhausts at the shift valves.
Do I have to relearn a 5R55W after fixing a ratio code?
Yes. Ford units built after 2002 use adaptive strategy, so the PCM has been compensating for whatever was wrong and those adapts do not clear themselves quickly. Erase keep alive memory, warm the fluid to 130 degrees Fahrenheit on the TFT PID, then run the garage shift relearn of five engagements each for Park to Reverse, Drive to Reverse, Reverse to Drive and Neutral to Drive, five seconds apart. Follow it with the drive learn at a steady 50 mph in fifth.
Sources
- Vehicle Service Pros — "Ironing out Ford 5R55N/S/W clunks and bumps," Wayne Colonna, president of ATSG, March 3, 2014. Backs the gear ratio table quoted from Ford's 5R55 W/S & N Transmissions Theory and Operation manual (W: 3.22 / 2.41 / 1.54 / 1.00 / 0.75; S: 3.22 / 2.29 / 1.54 / 1.00 / 0.71; N early and late variants); the overdrive planetary running 1:1 from input shaft to center shaft until the overdrive band applies; both overdrive planetary tooth counts and the 94/(94+38) = 0.71 and 72/(72+24) = 0.75 math; the tighter ratio tolerance on 2004 and later applications and the Lincoln LS sensitivity; the washer/adapter basic part number 7660 ordered by VIN as the identification method; and the full keep alive memory erase, garage shift relearn and drive learn procedure including the 54 C / 130 F fluid temperature and the 50 mph steady-state steps. vehicleservicepros.com
- Transmission Digest — "False Pretenses," Pete Luban, ATSG Technical Supervisor, February 1, 2005. Backs the code pairing logic and the servo bore test: pressure control solenoid B affects second and fifth so P0775 should appear with P0732 and P0735, with P0745 for solenoid A and P0975 for solenoid C; ATSG's help line experience that these have yet to be found electrically generated; the rules that a gear ratio code can occur without an electrical solenoid code but rarely the reverse, so ratio codes are addressed first; servo pin bore wear named as the number one cause of both the solenoid performance codes and the gear ratio codes on the 5R55N, W and S; and the test method of backing off the band adjustment stud, ensuring oil in the release side, then air applying the servo and observing what leaks at the pin bore. transmissiondigest.com
- Sonnax — Overdrive & Intermediate Servo Pin Bore Sleeve Kit 56361J-01K, product and cause data. Backs the servo pin bore mechanism: servo apply oil is fed through the center of the case bridge into the servo pin and reacts on the cover side of the piston, so a worn bore leaks apply oil into the barrel area of the case and degrades shift timing and servo/band apply pressure; increasing wear cross leaks release oil into the apply circuits where it exhausts at the shift valves; both servos are charged from the release side in reverse, producing delayed reverse; the unit's tendency to foam sump fluid from excess exhaust and valve body wear, causing fluid out the vent and improper fill indications; the listed symptoms of 1-2, 2-3 and 4-5 flares, gear loss, band lining failure, loss of overdrive and intermediate servo control, and codes 732, 733 and 735; and the wear-resistant aluminum sleeve repair with tooling that pilots and reams from the pin bore centerline rather than the servo piston bore. sonnax.com
- Sonnax — "Figuring Out the 5R55 Alphabet," Bob Warnke, September 19, 2007. Backs the valve body wear progression and the fluid history: the TCC modulator bore and main regulator bore wear first due to activity, and as cycle rate climbs the VFS 1, 2 and 3 modulator bores wear and reduce clutch and servo pressure, with adaptive strategy masking it until excess wear produces gear ratio codes or slippage, at which point the solenoid or servo pin bore is often blamed instead of the VFS modulator valves; the 24-tooth W and 38-tooth S overdrive sun gears; the solenoid base plate and filter being non-interchangeable between the N and the W/S, with mixing costing reverse, TCC apply and solenoid oil pressure; the pre-May-2005 early MERCON V factory fill problem, interim additive 4L2Z-19B546-AB under bulletin FSA 04B22 and the revised MERCON V (XT-5-QM) resolution; VFS solenoid priming with vacuum; and the post-2002 adaptive relearn requirement. sonnax.com
- Sonnax — Ford 5R55W/S Vacuum Test Guide. Backs the valve body test map and the VFS repair: the VFS1 modulator control valve is listed against flare shifts, low line pressure and pressure control out-of-range codes and is replaced with Sonnax 56947J-19K, which fits either of two locations and requires tool kit F-56947J-TL19 and VB-FIX; also identifies the solenoid feed limit valve kit 56947J-61K against codes 731 to 741, burnt bands and clutches and overheating, and provides the vacuum test locations and lower valve body valve identification used to check the main regulator and modulator bores. sonnax.com
- GEARS Magazine (ATRA) — "5R55N with Wrong Gear Starts and Bindups? Look for a Faulty Servo," Mike Brown, May 26, 2017. Backs the servo piston failure mode: a piston that has gone hard, torn a seal or delaminated lets release oil leak across to the apply side so the band engages when it should be released, producing wrong gear starts, bindups in reverse and manual low, and short-duration band or clutch failure with gear ratio codes; and the critical caveat that these servos may pass an air check because the damage is on the release side, with the in-vehicle check of raising the vehicle with the engine running in gear and attempting to turn both band adjustment screws. gearsmagazine.com
- NHTSA — Office of Defects Investigation complaints database, 2003 Ford Explorer, retrieved September 8, 2026. Backs the complaint volume figures cited: 1,313 total owner complaints on record for the 2003 Explorer, of which 356 are filed under the Power Train component category. api.nhtsa.gov
- ATRA — Technical Bulletin 1151, "Band Adjustment Chart," January 2008. Backs the band back-off specs: 2 turns on both bands for the 5R55N and 5R55W and 1999-2002 5R55S, and 1-1/2 turns on both bands for 2003-up 5R55S. atracom (PDF)
- ATRA — 2013 Technical Seminar manual, "Ford 5R55W/S Erratic Transmission Operation," pp. 112-120. Backs 2nd gear as forward clutch plus overdrive band and the 2-3 shift releasing the overdrive band while applying the intermediate band. atracom (PDF)