If I told you my car had a four-speed automatic transmission, but I wanted five speeds instead, you’d shrug. You’d say that swapping in a different transmission is a really big job. It’s simply not trivial to put more gears in your car. Unless you happen to own a Jeep, that is.
For a huge number of Jeep models built in the early 2000s, it’s entirely possible to enable secret bonus gears that were kept hidden from the factory. If you’ve got the right know-how, it’s entirely possible to put more gears in your Jeep without ever removing the transmission from the vehicle.
Wherever there is undocumented functionality in a vehicle, crafty owners will always figure out how to unlock it. Let’s explore how you can get extra gears in your Jeep on the cheap.
Hidden Functionality
Our story begins with a gearbox that Jeep called the 45RFE. The automatic transmission first debuted on the 1999 Jeep Grand Cherokee “WJ,” in models fitted with the 4.7-liter V8. Soon enough, the transmission found its way onto the 2002-2003 Jeep Liberty, the 2000 to 2002 Dodge Dakota and Durango, and the 2002 Dodge Ram.
At a glance, you could be forgiven for thinking 45RFE was a conventional four-speed torque-converter automatic. However, Jeep had actually done something a little off-beat with this transmission. At the time, most four-speed transmissions had just two planetary gearsets inside. These transmissions offered four forward gear ratios, depending on which of the sun and ring gears were held by the clutches in the transmission.
In the case of the 45RFE, though, despite officially being a four-speed, Jeep had included an extra third planetary gearset in the transmission. This would theoretically enable the transmission to have six forward speeds. Indeed, had Jeep gone this route, it would have been the first six-speed automatic transmission in mass production. However, as Chrysler brands are wont to do, they went a weirder route.
Jeep set the transmission programming for four forward speeds— 1, 2, 3, and 4—plus a bonus “second gear” ratio that was only used when downshifting. This extra gear is often referred to as “2 Prime.” If you were cruising in a higher gear, and then suddenly hit the throttle hard, the transmission was programmed to kick down into 2 Prime instead of 2. Where gear 2 had a ratio of 1.67:1, 2 Prime was 1.50:1. The higher ratio would slightly dull acceleration but allow you to go faster before having to shift back up into third.
That’s a total of five forward speeds, but Jeep stuck to calling it a four-speed in the marketing. However, Jeep’s fancy four-speed was already making waves in the industry. A technical paper released by the Society of Automotive Engineers in 1999 hinted at the magic lurking inside. “A sixth forward ratio, an additional overdrive ratio of 0.67, is available in the hardware,” noted the paper.
Would Jeep ever enable this fabled ratio in the transmission control software? That soon came to pass, when the automaker made updates for the 2001 model year of the Jeep Grand Cherokee. Models fitted with the 4.7-liter and 5.7-liter engines got the new 545RFE transmission, with six forward ratios (though marketed as a five-speed auto). It was still mechanically the same as the 45RFE that came before, and it still had the weird “2 Prime” gear that was only used for kickdowns. But crucially, Jeep enabled the use of a new sixth ratio in the gearbox to add an extra overdrive into the transmission. The ratios are outlined in the table below. Fundamentally, both transmissions have the same three sets of planetary gears, and the same total number of gear ratios available, the 45RFE is just programmed not to shift into the last overdrive ratio.
Jeep kept using the 45RFE configuration in a number of models after this point. 3.7-liter models of the Jeep Liberty used the 45RFE in 2002 and 2003, as did various models of the Dodge Dakota, Durango, and Ram across 2000 to 2002.
If you bought a Jeep fitted with the 45RFE, you might have been feeling a bit shortchanged. Those who purchased a later model Grand Cherokee were getting a whole extra overdrive gear, even though, mechanically speaking, they had the same transmission as you did. The 545RFE offered better fuel economy out of the box, and would nicely sit at lower RPM when cruising at highway speeds. Similarly, Ram, Dakota, and Durango owners might have felt shortchanged when Dodge changed over to the 545RFE for the 2003 model year.
Jeep’s decision left a tantalizing option on the table. Since the transmissions were apparently mechanically identical, all one would have to do is operate the 45RFE transmission with the 545RFE control logic to unlock the extra overdrive gear. Then, better fuel economy and drivability would be yours for cheap. You’d be getting a whole extra gear without even touching the transmission itself!
As it turns out, this is actually quite possible. It just requires laying your hands on a suitable 545RFE transmission control module (TCM), and installing it in place of your original 45RFE unit. Or, alternatively, flashing the 45RFE TCM with the updated 545RFE programming. Either was possible, though finding the right software to flash to the TCM isn’t easy if you don’t work for Jeep. At times, some forum users have offered to flash Jeep and Dodge 45RFE TCM up to the 545RFE spec. However, the easier route to this day is to grab an existing 545RFE TCM and swap it in place of the 45RFE unit. Importantly, this could only be done with 545RFE TCMs from 2004 and before, as later on, Jeep integrated the TCM functionality into other control units.
Of course, you could try to buy a 545RFE TCM from Jeep, but these modules are expensive from the dealership—costing hundreds of dollars. However, this is one of those joyful swaps you can pull off for cheap at the junkyard. The most common route is sourcing a TCM from a 4.7-liter Grand Cherokee from 2001 to 2004, which is the easiest swap into earlier Grand Cherokees, as well as Dakotas, Durangos, and Rams.
It’s possible to unlock the extra gearing in the Jeep Liberty, too, though some models require specific TCM swaps to function properly. Unfortunately, for some 2000 Dodge models, the TCM swap isn’t easily possible, as some examples were built with a TCM that used an earlier type of communication bus that isn’t compatible with the later Jeep Grand Cherokee units.
Swapping the TCM is a fairly easy job. It requires removing the airbox—a trivial job—and then one can access the module in the front fender well. The connector on the TCM can be removed simply by undoing an 8 mm bolt and tugging it free. From there, three further bolts hold the TCM to the vehicle, and then it’s ready to come out. From there, installing the new TCM is the opposite of removal. The new TCM might require some driving time for its adaptive learning to adjust to the transmission, but fundamentally, the swap is that simple.
Funnily enough, Jeep actually provided this upgrade itself for some owners. Per Technical Service Bulletin #18-025-01, issued in October 2001, some owners of 1999-2001 Jeep Grand Cherokees were occasionally suffering harsh shifting, with clunks or shudders in the drivetrain. This similarly applied to owners of 2000 and 2001 Dodge Dakotas and Durangos. In these cases, Jeep would flash new software to the TCM of affected vehicles to the 545RFE spec, unlocking the extra overdrive gear. In the case of 1999 and 2000 Grand Cherokees, an update to the separate Powertrain Control Module was also necessary. Basically, some owners went in to the dealership for transmission concerns, and came out with a whole extra gear in their automatic transmission!
On forum posts regarding the swap, owners typically report the 545RFE configuration dropping cruising RPMs by 300 to 400 RPM at cruising speeds. Gains of 1-2 mpg are commonly reported, too. This is no surprise, given the expected benefits of having a whole extra higher overdrive gear in the transmission. It’s also a pretty sweet gain in vehicles that typically only deliver 20 mpg or so.
If you calculate it out, swapping your TCM to a 545RFE unit can actually be economically advantageous. Let’s say you manage to score the right TCM for $50 at your local Pick-A-Part. If your Jeep steps up from 18 mpg to 20 mpg, you’ll pay for that upgrade in just a couple thousand miles at current gas prices.
The hack was most popular in the mid-to-late 2000s, in the years after Jeep made the upgrade from 45RFE to 545RFE. However, it’s still pursued regularly today by those looking to improve their early WJ Grand Cherokees and Dodges of the same era. The mod is just finicky enough that you’ll still find vehicles from that early period that don’t have their special extra gear unlocked.
Going Further
Despite actually having six forward ratios, Jeep still branded the 545RFE as a 5-speed transmission. That’s fair enough, given it only used five speeds during regular acceleration. However, if you want to turn it into a true six speed, that’s entirely possible in some of the later models fitted with this transmission. You just need to do some custom tuning.
One forum user over at Jeep Garage documented their method. They used a 2008 combined PCM/TCM unit, installed in a 2006 Jeep Grand Cherokee. With the aid of tools from HP Tuners, they were apparently able to program the transmission to shift up from second into 2 Prime and then later into third during regular acceleration. The method is also documented on the HPTuners forums, too.
This is not a common modification. Unlike adding an extra overdrive gear to the 45RFE, it doesn’t offer the same level of benefit. You’re really just getting an extra gear that’s really quite close to second before you eventually shift up to third. And that gear was already available on kickdowns, you’re just making it available during regular acceleration events, too.
Amusingly enough, though, Dodge and Jeep did end up effectively enabling similar operation themselves. In 2012, the V8 Dodge Durango, Jeep Grand Cherokee, and Ram 1500 all came out with the 65RFE transmission. It was essentially an updated version of the 545RFE with a better torque converter, and it used the same ratios—but it was now branded as a six-speed transmission. This was because you could switch it into “Electronic Range Select” model and use all six gears in sequence. When just left in regular “Drive,” however, it would still avoid shifting between the 1.67:1 and 1.50:1 gears in succession, just like a 545RFE.
Computer Control
This hack is a great example of what you can do with a bit of junkyard ingenuity. For the price of a cheap used transmission module, you can completely upgrade the behavior of your old Jeep or Dodge transmission. Getting a whole extra gear for $50 is absolutely wild, even moreso when it just involves undoing a few bolts and a single connector.
This is ultimately possible because of computer control revolutionizing the automotive world. These days, all functionality exists at the whims of the software in our vehicles. Modify the software, and you modify how your car drives. This hack is just an early example of how the driving experience can be totally changed via code.
Image credits: Jeep, Dodge, martinbuilt via YouTube screenshot, ebay
Joining late to the party, but the article says that this was used on 3.7s in Dodges and Jeeps in 02-03. That is not the case. It was only used on the 4.7 in those years, as the trucks and the WJ didn’t switch over from the 3.9 or 4.0 they were using until a few years later. The 3.7 in the smaller jeeps and later Dakota was always saddled with the cheaper 4 speed trannies.
I investigated doing this when I bought a 2001 Dakota new and the 545RFE appeared the next year. Unfortunately the truck blew up and was traded in before I the TCMs had a chance to become cheap and widely available. I found the 45RFE perfectly acceptable, as the kick down 2nd was great for passing on 2 lane highways. Fuel economy was an afterthought at the time as gas was cheap in Ohio (less than $1/gal if I remember correctly).
David Tracy has been holding out on all you Jeep owners.
Those ratios overall seem awfully short. A Ford Panther with a 4.6 and 4 speed auto cruises at around 2000 rpm at 70-75 depending on trans and axle.
My ’96 T-bird, 4.6 V8, 4R70W trans and a 3.27 trac lok axle would run solid 2000 rpm at 70 mph ’till it ran out of gas.
Ford always put pretty low axle ratios in their cars… my Mustang with 3.27’s cruised pretty nicely at low RPM’s until I put 4.10’s in it. Jeep used to do that as well- 3.07 gears in 5 speed equipped 4.0 Wranglers and Cherokees to keep the fuel economy up. But as the SUV wars heated up and the Grand gained weight they went to a higher ratio to keep it moving.
I had a ’99 WJ with a 4.0 Auto and don’t recall it cruising at much above 2000 rpm at 70 or so. Fuel economy was still terrible.
HOLY CRAP YOU JUST EXPLAINED SOMETHING THAT I INSTINCTIVELY KNEW BUT HAD NO “PROOF” OF. I remember driving my dads 2007 ram and the one thing i did not like truck was in slower traffic/ stop and go the damn transmission would never ‘feel’ like it was in the right gear. and it felt like it would gear hunt. i remember counting the shifts and i thought i counted 5 shifts on more than one occasion but i ‘knew’ this was a 5 speed auto so i just assumed that i miss counted!!
I think the issue would be that when you lightly accelerated it would shift to 3rd or 4th TOO quickly and kind of bog. so you would give the truck more gas and then it would shift all the way down the “2 prime” wich was WAAAYY more agressive than you was expecting with 380 horsepower the front end would almost lift off the ground and so you would back off the throttle because you did not INTEND to take off like a rocket ship. And then it would shift up to 5th and bog and sometimes the process would start all over again…
it’s like the truck’s transmission was stuck in ‘eco mode” but when you gave it barely any throttle it would all the sudden be in sport mode .. it was like dr jackyl and mr hyde!! I don’t think Chrysler really tuned the gear ratios or programming around the hemi they just dumped a transmission they had on hand and called it a day!
You can see why many people prefer manual transmissions. YOU decide when to shift and what gear to be in at all times.
Yes I love this types of obscure oem mods! And with old forums starting to die it’s great to document some of them more formally.
This is the kind of slightly obtuse Jeep shit that I love this site for.
we love slightly obtuse stuff that a ton of people get into doing. if you think of any, do hit up the tipsline 😀
This is a more elaborate version of the Allison automatic gear unlock. The Car Wizard reprogrammed the 5 speed in his bus project to a 6 speed, because the hardware was present. Of course any Autopian not named Mercedes Streeter is more likely to have a Jeep than a bus.
Yep, did that on my 02 1500 ram. It only shifts into the 0.67:1 gear at 60 mph and above. First few times it shifted into that gear it was a little harsh but smoothed out fairly quickly.
nice one!
Maybe Jeep was just way ahead of the times, and the plan was to unlock that sixth gear ratio with a subscription?
Joking aside, I can think of no other rational reason for that hardware to be in place but not utilized.
The product planning folks at Jeep really blew it there. I get that 2 and 2 prime were really close, but that could and should have been adjusted to give it six usable speeds.
I’d love to have been a fly on the wall for those engineering meetings.
My theory: “We don’t have time to finish the transmission calibration!”
“Just drop one of the gears, it’ll be quicker!”
As for rational reasoning — maybe it was the same thought processes of using the same wiring harness in both a base and premium model vehicles, and simply adding a switch to activate the feature.
I would imagine it’s more cost effective to have one transmission programmed three different ways for different application compared to three different transmissions.
It’s more likely that it doesn’t actually improve fuel mileage, it may put the engine closer to an inefficient rpm at certain speeds that might increase emissions, excessive load on the engine and additional noise or vibration. There are many reasons why engineers design engines to shift into specific gears at particular rpm. If it was as easy as making super-overdrive gears and having the engine lope around at 1,500 rpm all the time to get the same mileage as a Prius, they would be right on it.
I used to own an ’06 Mazda 3. The infotainment system in upper models had increased functionality, instant mpg, average mpg and miles to empty. The head unit was the same, the extra functionality could be unlocked using instructions found online. The special handshake unlocked features for free permanently.
Really cool!
I had a 2009 Ram with the 545RFE and 2nd prime always confused me especially when manual shifting. The cluster would show 2nd, but its 2nd prime. It would snow 3rd but it’s really 2nd. It would show 4th but was really 3rd etc. hahaha. I hated it so I never used it. Other than that it was a great trans didn’t have any problems with it. Changed the fluid/filter regularly and shifted smooth.
Oh no, that would bug me a lot.
Interesting article, but the titles that start with “Some Geniuses….” are really starting to be annoying. While I am griping, I also hate the “You can buy a 20 year old exotic for the same price as a new Kia” articles. No one is cross shopping an exotic and economy penalty box (nor should they). It’s just stupid. Don’t get me wrong, I love the site overall. It just that these gimmicky titles get annoying for those of us who read the site daily. What has made this site great is that it has good, quality content and is not just content that is created to get the most possible clicks. I don’t want that to change.
Yeah, I appreciate trying to keep a theme going, but it’s triggering my ‘clickbait alarm’, and leaving my cynical before I read a single word of the article.
Interesting feedback! Why cynical? Have we been publishing Some Genius articles that don’t live up to the form, in your book?
Ultimately – we have to strike a careful balance. We don’t want to tire the diehard readers, but we do want to create a branding so people know what they’re getting. Something we’re always thinking about!
There is nothing wrong with the article. I thought it was interesting. The title lets it down. Its a gimmick. There is nothing genius about what they are doing. It’s a cool mod, exploiting a interesting manufacturing choice by Jeep. Well worth the read, but the title makes me want to scroll past it with an eyeroll.
I guess it’s the autistic side of my brain that pushes the definition of ‘genius’ a bit further. There’s a fine line between genius and just plain clever.
That said, I’m not sure I could come up with a better running headline that also doesn’t sound like click bait. The internet can ruin so many things.
Enjoying the series, anyway. It just takes me longer to click on it.
Though I do agree the you can buy a 20 year old exotic for the price of a Kia type articles are annoying. I did genuinely cross shop 20 year old supercharged Jags with the 8th gen Honda Civic Si recently. I ultimately chose the Honda because manual transmission but the Jags were tempting with their big power, comfort and Aluminum bodies.
They are brand attributes.
Yeah the “Some Geniuses” and You can buy an old car for the price of a new things are getting tired and I’ve never bothered to click on any of the latter, and I don’t click on many of the former.
As long as they don’t get started with “This weird trick…” or “[Some item for the headline] and 8 other things we can’t stop thinking about!”
As long as it doesn’t mess with the IMO on those. Chrysler and it’s later embodiments and their IMOs are always a headache. The ones with the more Merc style you can kind of deal with. Still the most pain out of anything remotely normal.
What does IMO stand for?
“In My Opinion”
Immobilizer
Quick poll on the Autopian staffers – how many of them get the reference in the top graphic of this article?
Torch had to get it, but who else?
Side poll – how many people here had a Game Genie?
I still have the one for my Super Nintendo.
oh yeah, legit. but i spend tons of time in that world.
Wait, I could’ve had an extra gear in my 2003 Liberty!!!! And I’m just learning this now 11 years after I sold it! LOL. Of course this was the transmission that ate itself apart.
I had my ’99 WJ reflashed and got the extra gear. Highway engine speed went down by 200 rpm, but it didn’t make any noticeable difference on gas mileage. The guy at the dealership argued with me that it was impossible, and I had to tell him to just do the firmware update like I asked.
Is the “some geniuses” thing still doing its job? Because I am starting to feel “Some Geniuses” fatigue…
This is pretty wild of them to do on the Jeeps though.
I’m hoping that Some Geniuses on the Autopian staff can see that this is not the first comment complaining about this title structure
I feel like there’s been at least one a week since they “cracked the code” but that could be just me noticing it more.
Some Geniuses just don’t read those articles anymore. And I usually don’t either.
That’s really interesting! Is it because you’re sick of engine swap/transmission swap content, or because the headline just annoys you too much that the content doesn’t matter to you anymore?
For me it is the headline that annoys me too much. In this case I clicked on it since I did know that they sold a 5 speed as a 4 speed that gave a different 2nd gear ratio going down vs going up.
The content is usually proves to be more interesting that I give it credit for when I see the headline.
That said, I’m likely to never have the need or ability to do whatever the article is about, so in some sense the headline just says “you’re not a genius”. That’s true enough, but I kind of don’t really need the remember, ya know?
Blame Google. I know Matt commented on one of these articles a while back that they found they do much better with the “Some geniuses” article titles than without, even for the same type of content. For me it’s a small price to pay to keep the site financially viable.
Allison transmission also did this for a very long time, on multiple transmissions. The MD3060 just needs programming updates, but the 1000 and 2000 series can go from a 5 speed to a 6 speed by swapping in the 6-speed valve body, and reprogramming it. The 1000 series were found in the first Duramax trucks, as well as 8.1 liter pickups, and were later upgraded to the 6-speed version from the factory. Not as easy (or cheap) as upgrading the Chrysler stuff, but, still a head-scratcher why they didn’t just launch as 6-speeds.
45RFE: All of the cost of a six-speed, with none of the marketing benefits. Makes perfect sense.
Right?! It just seems soooo dumb to have a gear and lock it out for no real reason. No wonder the Chrysler corporation is on the verge of going bust every 2-3 years
It was so they could later advertise a 5-speed and then a 6-speed. Planning ahead!
It would be fascinating to know the logic behind shipping a transmission with 6 gears and disabling 1.5 of them. Was it purely a marketing play so they could sell people on the “upgraded” transmission down the line? Was the transmission calibration not ready when it first shipped? Was there a miscommunication between the PCM people and the transmission hardware people or some other hilarious corporate hijinx?
Chrysler/FCA/Stellantis seems to enjoy playing games with transmission marketing.
There was a similar kerfuffle surrounding the RAM ProMaster vans a few years ago, when they were advertised as having 9-speed transmissions – and yes, the gearbox contained 9 forward gear ratios – except the TCM was programmed to never, ever upshift into 9th gear.
Same trick was with the kl cherokee iirc, that had the fiatsler 9 speed, and never hardly ever used 9th gear, like why the hell even have it.
In the challenchargers, the 8sp trans barely ever uses the last 2 gears, drove a friends rt and just cause, manually forced it into 8th on the highway, and lo behold, inwas doing around 70 at just over 1500 rpm or so, imagine the fuel economy if theydve let it normally work that way.
Lower rpm doesn’t correlate to better economy, just increased engine wear, sluggish performance, and annoying “gear hunting”.
True, it doesnt always.
The 5.7 hemi on flat ground would have enough torque and power to maintain that box at 70 in such a low rpm.
Most trans these days drop 1 or 2 gears with converter unlock when going from cruise to more throttle application, then settle right back in.
My 4l60e when going from cruise to more throttle will quickly unlock converter to scootch along, then relocks again.
So for these new trans 20 years later to have 7,8,9 gears and not use them all is odd as it is wasteful.
I would like to see an extended run with 8th gear and watching vitals to see how itd actually do.
It sounds like it wasn’t offered on the 3.7, which probably lacked the power to pull the overdrive gear except under uncommonly gentle highway circumstances, so they disabled it to save the customer the annoyance of constant gear hunting (a problem I find unacceptable in modern autos that have too many speeds). Making one transmission was cheaper than manufacturing and logistics for two different ones.
That’s another plausible explanation.
Possibly because it had some drawbacks. It makes the vehicle slower and needs to downshift more often, it could be putting the engine at a less efficient or noisier rpm at cruising speeds. The additional load on the engine likely reduces the life of the engine, etc.
Today they would try to force a monthly subscription on you to get the gear you already paid for….
I love this kind of stuff, where manufactures have included features as standard to standardize builds and reduce cost, but omitted to the functionality on lower trims. For example. My brother bought an early 07 FJ Cruiser with a rear locker, but without the ATRAC you had to pay extra for in 2007. Solution? Buy the OE ATRAC button from Toyota and plug it into the harness that is behind the dash waiting for it. Boom. New feature unlocked.
Same story with the center differential lock button on 80 series Land Cruisers. USDM cruisers didn’t come with a way to manually lock the center diff, it only happened when you shifted into low range. But the harness is there and the function is only a button away from being fully functional. Ditto seat heaters – the harness is there for seat heaters that were never offered in the US, but you can buy the switches from Japan, put in your own seat heating elements and boom…seat heaters.
I want this to happen to KTMs that come fitted from factory with things like quick shifters, but they are locked behind a software block.
Came here to post about the FJ80. I read about the mod on the forums. When I had mine the diff lock switch was close to 100 bucks, but I learned that a hazard switch plugged right in and were like 10 bucks on ebay so mine had two hazard switches. IIRC all the Toyotas used the same hazard switch
I had a 2001 WJ with the 545RFE and that transmission, I just hated it for one reason: 5th gear. That ratio was just impossible to drive in on even the flattest of highways so it would be constantly shifting 543454345… with just the slightest application of the throttle. Holy crap was it annoying. Granted, the truck was quite heavily modified for off-road duties, but still. The 2nd Prime was a curious, if unnecessary Chryslerizm.
This sounds eerily similar to all the times I had to borrow my brother’s ’15 Tacoma. I don’t know why the thing even had a 6th gear, because I don’t think I ever came across a road flat enough to stay in it for more than 3-seconds.
I love when people are able to unlock functionality that the OEM didn’t originally offer.
Some mad men were able to turn the 4l80e from a 4 speed to a 6 speed by fitting a different valve body and an additional solenoid. I guess this was super useful for those looking for a 6 speed that could handle a ton of torque.
Whaaaaaa, please go on here
Makes me wonder if a 4l60 would have this ability.
I’m not sure if anyone sells just the valve body and solenoid to make this happen but there is at least one vendor (TCI) selling 6 speed 4l80e transmissions. They claim they are capable of 850hp. It does look like they need to use a TCI controller to operate the transmission, which makes sense. Ultimately these probably have a pretty narrow use case for where they actually make sense.
I had to look this up and lo and behold, theres a couple of vendors who do it.
Tci indeed seemed to have a whole complete kit, id gander would be great for tow rigs without the whole need for a literal 6sp swap or a gear vendors.