What causes an incorrect gear ratio?

The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes), controls automatic transmission by using multiple gear ratio and increase the vehicle speed to maximize the engine’s power output. Newer vehicle models are equipped with more than four gear ratios for fuel efficiency. The PCM decides when to shift up or down between gears, based on the vehicle speed vs. throttle position. It does so by using the input coming from various sensors to verify the correct operation of the transmission and all its components.

The TCM (transmission control module) calculates gear ratio based on data from the transmission input shaft speed and output shaft speed sensors. The TCM compares the calculated gear ratio to the known gear ratio for each commanded gear. If the TCM detects an incorrect 1st gear ratio while decelerating in LOW, indicating no engine braking within the transmission, then DTC P0730 sets.

What causes this problem with the Incorrect Gear Ratio?

• Insufficient or dirty transmission fluid
• Clogged fluid filter or worn pump
• Solenoid, torque converter clutch or internal blockage
• Internal blockage in transmission main control
• Mechanical failure inside transmission
• Faulty shift wirings or solenoids
• Faulty transmission control module
• Defective torque converter clutch

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Listed below are some possible causes of the formation of the onboard diagnostic II (OBDII) diagnostic issue number P0730;

• Transmission fluid is contaminated 
• Filter or pump has become clogged or worn out
• Internal obstruction or blockage in solenoid in the torque converter
• Internal blockage in the main transmission control 
• Mechanical damage inside transmission
• Faulty shift wirings or solenoids
• Faulty transmission control module
• Defective torque converter clutch

Symptoms

Listed below are some possible symptoms associated with the P0730 error code. However, the most frequent indications and symptoms linked with P0730 is a decrease of the RPM limiter.

• This code will cause the Check Engine Light (CEL) on the dashboard to light.
• The signs of a misfire may be present
• Transmission slipping/high/low, gears are not moving in a proper manner
• When travelling on the highway, the vehicle comes to a complete halt.
• Vehicle shifts very slowly or does not shift into the appropriate gear at all.
• Too long in a low gear or too long in a high ratio might cause the engine to shut down.
• There is a reduction in fuel economy.

Diagnosis

To see real-time information and troubleshoot error code P0730, OBD-II scanners are utilized. Upon clearing the codes, a test drive will be performed. If, after a test drive, an error code is still shown, the correction communication has failed.

As per the manufacturer’s guidelines, torque converter stall speed tests can be done. Before performing the test, go through your owner’s handbook. Engine stall speed may not be within original standards if a torque converter or internal gearbox issue is present. When P0730 is shown together with other ratio error codes, this may be the problem. Fluid pressure is frequently used to regulate the torque converter clutch, internal clutches, and bands. The solenoid should also display a fault code if there is an electrical problem.

Inspect the transmission fuse, if it is found to be faulty. Verify that none of them is defective before proceeding.

As a next step, inspect the transmission wire harness and connectors for damage. 

Next, test the Torque Converter Clutch (TCC) solenoid itself and confirm that the Transmission Control Module (TCM) has been instructed to turn it on by sending a signal to the solenoid. This type of diagnostic is a bit more complicated and may require the assistance of a professional. Check the following things while checking the torque convertor clutch.

• Inspect electrical connections and cables connecting sensors to the transmission control module.
• Inspect the transmission speed sensor for any broken cables.
• Check that the transmission fluid is at the correct level and the transmission sensor and solenoid wire are in good operating condition.

Diagnostic Mistakes to Avoid

Misdiagnoses include internal transmission problems and engine misfiring, which are both common errors. Transmission fluid that is filthy or low may be the cause of the symptoms you are experiencing. Replacing or topping up the transmission fluid may fix the transmission problems that are producing the fault code.

How Serious Is This Code?

There is significant variation in the severity of the P0730 code among applications. Minor problems can cause the code to activate since any slowdown in transmission speed causes it to activate in any gear. It may also occur when there is a serious transmission malfunction, such as a blown fuse, which would result in the car not being able to shift gears.

In the event that the P0730 code arises, a technician certified by the manufacturer should diagnose the problem. Most of the time, after the code is reset, the problem disappears, particularly if the Check Engine light comes on at the restart.

What repairs can fix the code?

Depending on the diagnosis, the fixes are as follows:

• The most prevalent reason for this error code is likely to be a low or filthy transmission. Replace the filthy fluid to remedy the problem.
• All electrical connections and cables that link the sensors to the transmission control module should be inspected and repaired as necessary.
• In and around the transmission control module, repair or replace broken or corroded cables with new ones.
• The transmission's wiring and fluid may still need to be fixed or replaced, even if they are in good shape.
• If the torque converter, shift solenoids, or pump are malfunctioning, the transmission must be removed.

Related codes

• P0729
• P0731
• P0732
• P0733
• P0734
• P0735
• P0736

Conclusion

DTC P0730 is a complex error and can cause a serious problem to the vehicle. An expert mechanic with his dedicated tools can fix the issue. Ideally, the code should be diagnosed and corrected by a professional who is fully certified as soon as feasible.

OBD-II Trouble Code P0730 refers to an Transmission Incorrect Gear Ratio

Here is what a P0730 means, in simple terms

An automatic transmission is designed to configure an optimal torque and power combination in order to provide the driver with desired speed and rate of acceleration. The system is being constantly monitored by the transmission control module (TCM). If the TCM notices a RPM difference between the transmission output sensor and input RPM sensor that is greater than a predetermined value, the TCM triggers a P0730 trouble code.

What caused my vehicle to set a P0730 trouble code?

A P0730 can be triggered while shifting between gears or when driving at a steady speed in any gear the transmission is designed to utilize. P0730 is usually triggered when there is a problem during shifting gears. Being it a generic trouble code, P0730 does not necessarily pinpoint any specific gear ratio failure. In other words, the trouble code does not indicate which one of your vehicle's gear(s) is failing. Instead, it simply advises that there is a problem between the transmission's expected output and input RPMs. Other related codes include related to the P0730 include: P0729, P0731, P0732, P0733, P0734, P0735 and P0736. These should be fixed first before fixing the incorrect gear ratio problem. More than likely the issue causing the P0730 will be resolved during the correction of the prior codes.

Here are some common faults which may cause a P0730 to be stored with the engine computer system:

• Low or dirty transmission fluid (check this first)
• Worn pump or clogged transmission fluid filter
• Torque converter clutch defect
• Internal mechanical failure
• Faulty shift solenoid and/or wiring
• Faulty transmission speed sensor and/or wiring
• Faulty transmission control module

What symptoms will my vehicle experience when trouble code P0730 is set?

• Your vehicle's check engine light (CEL), Malfunction Indicator Lamp (MIL) or Service Engine Soon light will be illuminated and freeze frame data stored with information regarding engine sensor data at the time when the incorrect gear ratio was detected by the TCM. Trouble code P0730 will also be recorded in the ECC ROM memory.
• Bad fuel economy.
• Unable to drive at high speed.
• Transmission not shifting to low/high gears.

How can I fix a P0730 problem and where should I start?

If so, move on to inspecting the transmission fuse(s). Ensure none are defective. Next move on to checking the wiring harness and wiring connections to the transmission for damaged. If the wiring to the transmission control module and torque converter clutch solenoid are not damaged, your next step would be to test the TCC solenoid itself, as well as verify the TCM is commanding the solenoid on (power at solenoid when activated by TCM). This diagnosis is a bit more complicated and may require an experienced technician. Possible fixes to clear a OBD-II Trouble Code P0730 include:

• Inspect electrical connections and wires connecting sensors to the transmission control module.
• Repair or replace any damaged wires in and around the transmission control module.
• Repair or replace any damaged wires in and around transmission speed sensor.
• If transmission fluid filled to proper level and transmission sensor and solenoid wiring in working condition, components within the transmission may need to be repaired or replaced.

• You may drive your vehicle with a P0730 however keep in mind your vehicle will not pass a smog inspection.
• Problems with the incorrect gear selection may cause drive-ability symptoms.
• The check engine light or malfunction indicator lamp will be illuminated as long as a P0730 is recorded in the ECC.

posted by SmogTips Support 03-14-2019