The value of knowing your transmission gear ratios - Transmission Digest

The value of knowing your transmission gear ratios

If you have ever watched the movie Forrest Gump, you know the quote, “Life is like a box of chocolates. You never know what you’re going to get.” That quote holds a lot of value in the transmission industry these days. 

Transmissions may look the same from the outside, however, it is what is on the inside that can make a difference between a successful repair or a costly one. What am I talking about, you ask? Gear ratios.

The modern car is very integrated from one module to the next and from one gear ratio to another. When you are replacing parts, or the entire transmission assembly, you need to know what ratios you are removing so you can install the correct one. Otherwise, you may create a problem that you did not have with the original transmission.

One example was a customer with a 2015 Jeep. This vehicle came in with a P0215C code and a rough coast downshift. This vehicle was fitted with a 948TE 9-speed transaxle with a 3.2L engine and a 4WD drivetrain. It arrived from a local dealer where they installed a used transmission. The used replacement transmission solved the unknown problems with the original transmission; however, it now had a recurring coast downshift clunk and a P0215C with the replacement transmission. It did not have these problems with the original transmission according to the dealership technician. 


The first item on the diagnostic hit list is the P0215C. The downshift clunk is most likely being induced from the DTC P0215C which is not allowing full adaption with the code present.  

DTC P0215C definition: Vehicle speed to wheel speed correlation out of range.

The definition means that the powertrain control module (PCM) has detected a discrepancy between the vehicle speed sensor and one (or more) of the wheel speed sensors.

The vehicle speed sensor and the wheel speed sensor are both intended to detect vehicle speed. The PCM is constantly monitoring vehicle speed when the vehicle is moving forward. The individual wheel speed sensors are constantly monitored by the anti-lock brake control module (ABCM), or electronic brake control module (EBCM). These two controllers share data via the CAN Bus network and compare the signals anytime the vehicle is in forward motion. 

If either controller detects a discrepancy between the vehicle speed and the wheel speed that exceeds the maximum threshold, the code P0215C will be set and stored. Also, the malfunction indicator lamp will be illuminated.

Causes for the P0215C code may include:

  • Excessive metallic debris on transmission speed sensor 
  • Defective wheel speed sensor
  • Cut or damaged wiring or connectors
  • Broken, damaged or worn reluctor gear teeth
  • Mechanical faults with transmission gearing
  • Faulty PCM, ABCM or EBCM
  • Interference or damaged wiring in the CAN Bus system

First things first. Now that we know the definition of the P0215C code, and what will set it, I asked the shop tech to provide some scan tool information. In this example, the scanner data graph for the vehicle speed sensor is running slower than the wheel speed sensors. I researched my archive of Snap-On data movies for this transmission and found that the readings indicated were incorrect. This was the first clue into the P0215C code. The vehicle speed sensor assembly reads off the teeth on the final drive pinion gear.

To further complicate matters, these vehicles are available with several powertrain configurations and ratios:

  • 2.4L FWD
  • 2.4L AWD with single speed transfer case (PTU) referred to as “Active Drive”
  • 3.2L FWD
  • 3.2L 4X4 with 2 speed transfer case (PTU) and 2 speed rear differential
  • 3.2L 4X4 with 2 speed transfer case (PTU) and 2 speed locker rear differential 
  • 3.2L AWD with single speed transfer case (PTU) referred to as “Active Drive”

Both the 2.4L and the 3.2L transmissions are available with a trailer tow option. Vehicles equipped with the trailer tow option will have a lower transmission final drive ratio. The 2.4L engines have a final drive ratio of 3.73. The 2.4L engines, with the trailer tow package have a final drive ratio of 4.08. The 3.2L engines have a standard ratio of 3.25, and the models with the trailer tow option have a 3.51.1 ratio. The rear differential is also available as a locking type as well. Please keep in mind this information is for the 2015 model year only. The ratios and options may vary based on the production year and model.

Once the diagnostic investigation was under way, I looked up the part number for the transmission assembly by the VIN number. The search results indicated that there was only one selectable part number listed for this VIN code, it had a 3.51 ratio. The listing also had the part number for the 3.21 ratio unit as well. The 3.21 unit could not be selected from the list, which indicated to me that it was not the correct transmission for the VIN number entered into the search. To satisfy my curiosity, I did another search without the VIN. I discovered that I could choose either ratio; however, I was prompted to order by the VIN.

Service transmission part number assembly: RL225760AP 3.21 Ratio

Service transmission part number assembly: RL225761AP 3.51 Ratio.  

Fortunately, the repair shop was given the original transmission. The ID numbers on the tags (Jeep only) were different between the original transmission and the used replacement as seen in Figures 1 and 2.

In my search efforts to determine what the meaning of ID tag numbers were, I learned what you can see in Figure 3, at the top of the page).  

The transmission plant production number on the tag is the number that is associated with the service replacement transmission part number listed by FCA. A search of the service replacement part number, not the plant production number, indicated that the vehicle had the wrong ratio installed. The used transmission that was installed had a 3.21 ratio when this vehicle required a 3.51 ratio. This tells us the vehicle was built with the trailer tow option. 

The correct ratio transmission was installed, the rough downshift and the P0215C was eliminated.

You May Also Like

How the Ford engine stop/start system affects transmissions

2018 and later Ford Escape vehicles equipped with a 1.5 L Eco-Boost, 2.0-liter turbocharged engine or the 2L VCTi engines, and the 6F35 transmission, have an engine stop/start system. The stop/start feature can be disabled by the driver and will remain disabled after each key cycle until reactivated by the driver. Some Ford Fusion and


2018 and later Ford Escape vehicles equipped with a 1.5 L Eco-Boost, 2.0-liter turbocharged engine or the 2L VCTi engines, and the 6F35 transmission, have an engine stop/start system. The stop/start feature can be disabled by the driver and will remain disabled after each key cycle until reactivated by the driver. Some Ford Fusion and Edge models will also have the engine stop/start feature. The reason for this was to improve fuel economy and lower tailpipe emissions.

Chrysler ZF8 generations 1 and 2 identification guide

In 2019, some Chrysler/Ram/Jeep applications that utilize the ZF8HP transmission moved to a second-generation unit with a new designation and numerous changes for better performance and durability. Gen. 1 units are classified as 8HP45, 8HP70 and 8HP90; while Gen. 2 are classified as 8HP50, 8HP75 and 8HP95. Internally, the Gen. 2 transmission had numerous hard

When a transmission problem isn’t a transmission problem

Let’s take a look at three examples of times when a car’s issue seems to be a transmission problem, but a closer look reveals another culprit. Related Articles – A part for every need: Hard parts supplier listing 2023 – Breaking parts: Pressure regulator valve and bore blues – Transmission fluid hydraulics Case study 1:

Breaking parts: Pressure regulator valve and bore blues

One of our ATSG members, Bob at Trans Tek, recently shared with us an experience he encountered with a 2011 GMC 3500 Mini School Bus with a Duramax diesel engine in front of a 6L90 transmission. It came in to the shop slipping, along with having no second or sixth gear. After the transmission was

Transmission fluid hydraulics

To understand why using the correct transmission fluid is necessary, you first have to know how the transmission fluid flows inside an automatic transmission. Related Articles – 2023 State of the Powertrain Industry – Powertrain industry directory and buyer’s guide 2023 – Shift Pointers: No ball, no reverse Fluid paths The journey starts in the


Other Posts

The multi-functional Clutch 1 in Nissan’s CVT, part 1

Nissan’s Hybrid RE0F02/3H CVT transmission by Jatco (JF019E) can be found in vehicles such as the Nissan Rogue and Pathfinder as well as the Infiniti QX60. It has its traction motor located where the torque converter would normally be (as you can see in Figures 1, at the top of the page, and 2, below).

Critical wear areas and vacuum test locations: GM 10L and Ford 10R series

Sonnax has provided the following guide on critical wear areas and vacuum test locations for the GM 10L series and the Ford 10R series. Technicans working on these models should find the following four pages helpful. Related Articles – Announcing the winners of the Top 20 Products and Tools contest – Shift pointers: A 4T65-E

Scope testing the Ford 10R80

Recently, we at Certified Transmission had a chance to do some work with the Ford 10R80. We have easy access to test vehicles since our owner also owns a used car dealership. For our R&D testing we used a 2019 F-150 equipped with a 5.0L engine and the 10R80 transmission. I got to play around

Shift pointers: A 4T65-E that wants to move in Park and Neutral

When conducting ATSG seminars, as we are usually covering a specific piece of tech, we’ll often tell attendees that if they put this together wrong, they should let us know what happens. Just recently, Ricky Hodgkinson from AACTION Transmission did just that. He was kind enough to share an incident he recently had with a