Modern automatic transmission systems are often extremely complex. Your average gearbox is a maze of electronic, mechanical, and hydraulic components that are all working in unison. Diagnosing an issue within such complex systems would be extremely difficult without dedicated check engine light codes to point you in the right direction. The P0730 code is one of them. 

This code is fairly common and can occur on most modern vehicles fitted with automatic transmissions. Join us as we explore what causes this code, how to troubleshoot it, and how to fix it. 

What is the P0730 Code, and What Does It Mean? 

The P0730 is the diagnostic trouble code that reads as follows — Incorrect Gear Ratio Detected. It occurs when the ECU detects an RPM difference between the engine input and the driveshaft output. 

Since your ECU relies on a whole range of metrics to tell the transmission when to shift gears, any disparity between the engine input data and the driveshaft output data is cause for alarm. This particular code is on the generic side, meaning that there are multiple automatic transmission issues that can trigger it. 

What Causes the P0730 Code? 

Despite being a generic code, you’ll find that most of the causes of the P0730 are related to internal components of your transmission, whether it’s your transmission fluid, your torque converter, or anything in between. That being said, some can be difficult to both diagnose and repair, while others are far easier to rectify. 

Here are some of the common causes:

• Low transmission fluid 
• Torque converter/clutch pack failure
• Faulty shift solenoids
• Speed sensor issues
• Clogged transmission fluid system
• Electrical issues

Low/Worn Transmission Fluid 

This is the most common failure point when looking at this trouble code. Transmission fluids are often called lifetime fluids, which many car owners think means that they never need to be replaced. This is, however, only a specific time period that the manufacturer has designated as the life of the vehicle.

As a result, there are many cars out there that run worn and contaminated fluid inside their transmissions. Worn fluid is nowhere near as efficient at providing the hydraulic pressure, lubricating the internals, and cooling the critical components of the automatic transmission. Consequently, worn fluid is also the most common root cause of many transmission issues. 

Low automatic transmission fluid levels can also cause all kinds of problems. Considering that just about everything inside an average automatic transmission is actuated by this fluid, things start failing quickly when there isn’t enough fluid to go around. Loss of hydraulic pressure can hinder gear change solenoid activation, power transmission, as well as all kinds of other critical functions. 

If your car is fitted with a transmission fluid dipstick, make sure to check the levels and the condition of the fluid on a regular basis. You can avoid so many issues just by staying on top of your maintenance. 

Torque Converter/Clutch Failure

Automatic transmissions use a torque converter/clutch combo controlled by the PCM to transfer power from the engine to the transmission. As a side note, dual-clutch (DCT) and continuous variable (CVT) transmissions use different codes. Damage to the clutch or torque converter can cause a P0730 code. 

A compromised torque converter or a failed clutch pack won’t be anywhere nearly as efficient, which can either cause issues with other transmission components down the line or simply create a power transfer bottleneck in the system. 

Faulty Transmission Solenoid

The transmission solenoid controls the flow of transmission fluid through the valve body. Your automatic transmission uses at least 2 or 3 of these solenoids, but often more. That being said, solenoids have their own failure code (P0750), but can cause a P0730 as well. As far as what can cause solenoid malfunction, there are many factors involved. Contaminated or worn fluid is a common cause of transmission solenoid failure, but so are electrical issues. 

You won’t see transmission solenoids fail too often, but they are worth checking out if you’re logging a P0730 code and one of your main symptoms is a gear change issue. 

Speed Sensor Issues

The speed sensor communicates how fast the output driveshaft is moving, allowing the transmission to shift to the correct gear. Failure means that the transmission will either shift into the wrong gear, causing damage, or not shift at all.

It often causes a mismatch in output and input RPM, which leads to the PCM registering a P0730 code.

Clogged Transmission Fluid System

The system of valves and fluid lines is prone to clogging because of carbon. Of course, the fluid is designed to carry contaminants away and prevent buildup, but even a small amount of build-up over a long period can cause issues.

A transmission oil pump is also a potential point of failure when you have a P0730 code. Clogging means that your vehicle changes into the wrong gear or refuses to shift into specific gears, as the fluid pressure is altered.

What Are the Common Symptoms of P0730 Fault Code?

Just like with every other fault code out there, the P0730 triggers a set of symptoms. Although some of these are commonly related to other transmission and sensor codes, others will bring you closer to identifying the causes and fixing the issue. Some of the primary symptoms include:

• Check Engine Light
• Improper gear shifting
• Reduced Fuel Economy

Check Engine Light

The check engine light is the first indicator that there is an issue with your vehicle. A P0730 code will cause your CEL to illuminate. A CEL on the dash is an immediate sign that you should stop as soon as possible.

Improper Gear Shifting

In a functioning system, your transmission will shift into the correct gear based on the engine RPM and the speed of the vehicle. Difficult acceleration at low speed, transmission hang when reaching higher rpm, or not shifting, is one sign of this trouble code.

You can also look at the gear indicator display and compare it with the vehicle speed. Most drivers are familiar with their car’s shifting pattern, so you’ll feel that something is off. 

Reduced Fuel Economy

Depending on the cause of the issue, you may experience poor gas mileage if you have transmission issues. A disruption in the flow of transmission fluid causes slippage and slow shifting. Losing torque means that your vehicle will use more fuel to achieve the same amount of power.

How to Diagnose and Fix the Cause of P0730 Code 

Now that we know the background of the P0730 code, what causes it, and which components could be at fault, it’s time to discuss ways to diagnose and fix the issue. 

OBD II Reader

The OBD II reader allows you to interface with the engine computer and identify issues. Run a complete scan of the system and check the logs. Although many issues can cause the same trouble code, having an insight into your ECU’s logs is essential when it comes to figuring out what went wrong and why. 

You can use live data on the OBD-II reader to diagnose a transmission solenoid issue. The shift solenoid should be closed when the vehicle is in neutral and open when the vehicle is in park or drive. Make sure that there is something preventing the vehicle from moving if you are performing the test while the wheels are on the ground.

Check the Transmission Fluid

This is one of the principal causes of the P0730 trouble code. Good transmission fluid is a clear dark red. Contaminated fluid is a dirty brown-red color and often contains soot or metal flakes. Worn fluid also gives off a smell of burnt toast. If you notice any metal flakes on the dipstick, take note of that as they could indicate a more severe mechanical issue somewhere inside the system.

Always consult your owner’s manual, as some manufacturers use different colored fluids for their automatic transmissions. As a note, replace transmission fluid and filter every 50,000 to 60,000 miles, even if you have a “lifetime” fluid.

Diagnosing the Shift Solenoid

The shift solenoids are a set of electronically operated valves that control gear shifting and other functions inside the transmission. Shift solenoids force hydraulic fluid through different parts of a maze-like structure of the valve body depending on what your ECU wants to do. There is a specific trouble code for shift solenoid failure, but it can also cause a P0730 because it controls shifting gears. 

Do a quick check on the valve body for any mechanical damage as it can indicate internal issues. Damage to the internal components of the transmission usually causes problems with the solenoids. That being said, some transmission solenoids can be accessed without having to remove the transmission fluid pan, so check your car’s service manual for more precise information.

If you can remove the solenoids, you can probe them with a multimeter to check for resistance, but also bench-test them using a 12V battery. Most solenoids function in two states — opened and closed. If a solenoid is stuck open or stuck closed, you’ll know that it’s bad. 

Internal Damage Inspection 

Unfortunately, this is where most DIY troubleshooting/fixing stops. Checking for internal damage to the automatic transmission implies dropping the transmission and tearing it down on a bench somewhere. This requires resources, facilities, and a vast amount of knowledge, which is why most people leave that to a shop. 

Does P0730 Clear Itself?

The P0730 is the type of code you’ll want to clear using an OBD II reader. Doing so is necessary to confirm a fix without having to drive around until the code clears itself. Do a manual wipe of the code and monitor the logs closely until you’re absolutely certain that your issue has been fixed. 

Is It OK to Drive with a P0730?

Nope, it is not OK to drive with an active P0730. Doing so puts you at risk of doing more damage to the transmission, which can turn a potentially simple issue into an expensive mistake. Do yourself a favor and pull over as soon as you see a CEL pop up on your dash. 

How to Make Sure P0730 Doesn’t Come Back? 

The best way to do so is to fix the issue using quality parts and maintain your transmission using products made by renowned brands. Here at eEuroparts.com, we offer a wide range of genuine, OEM, and quality aftermarket parts for most European makes and models. 

To find what you’re looking for, simply head over to our store, select your vehicle using our built-in navigation tool, and search for the parts you need. Our system will return only those products that are a guaranteed fit for your car!