Trouble codes related to automatic transmissions are often the most dreaded ones. Not only are transmissions difficult to reach, but they are generally integrated systems that are the complete opposite of DIY-friendly. Even then, some transmission check engine light codes are worse than others. 

The P700 code we’ll cover today is arguably one of the last codes you’ll want to see when you scan your car. In this short guide, we’ll do our best to cover the causes, symptoms, and potential ways that you can fix this code at home. 

What Is the P0700 Code, and What Does It Mean? 

The P0700 is the trouble code for a “Transmission Control System Malfunction.” This code appears when the ECU registers a drop in voltage in the transmission control module (TCM). What usually happens next is your vehicle entering the limp mode. Any TCM related fault code can be a tricky one because there is a real chance that your TCM is malfunctioning. 

What is a Transmission Control Module? 

The transmission control module is the main module that governs the operation of your automatic transmission. It’s essentially a computer whose only purpose is to make sure that your transmission is always in the right gear and working as efficiently as possible. With that in mind, it’s easy to just how much of a headache a malfunctioning PCM could cause. 

Where Is the Transmission Control System Located?

You’ll find this system on top of or near the transmission. The valve body is located on the side of the transmission and the TCM on top. The location differs between vehicles, so make sure to consult your car’s service manual in order to find yours. 

What Causes the P0700 Code? 

As with most transmission issues, the causes of a P0700 are isolated to the transmission itself. Diagnosing the issue is hence not that difficult. What is often far more difficult is fixing the issue. Here are the common causes of a P0700 trouble code:

• Transmission control module failure
• Valve body issues
• Wiring harness damage
• Failed transmission control solenoid 

Transmission Control Module Failure

Most times, you will find that TCM issues are caused by a manufacturing error or other production defects. An average TCM usually lasts for the lifetime of the vehicle and isn’t really a component that is known to have a high failure rate. However, like any component, it can fail. TCM failure is usually caused by an electrical anomaly. With that said, physical damage to the unit, whether it be kinetic or water damage caused by a flood, will also do the job. Either way, a faulty TCM is one of the main causes of the P0700 code. 

Valve Body Issues

The valve body is a hydraulic system of valves responsible for shifting gears in an automatic transmission. When the fluid dries up or leaks occur, the inner components seize or break and come loose. If this happens, you can no longer shift properly. It will also cause the P0700 trouble code.

Wiring Harness Damage

Damage to the wiring harness is a cause of vehicle problems. Although modern vehicles shield their wires better, they are still vulnerable to breaking where they meet the component. This can either cause low voltage supply or incorrect readings.

Failed Transmission Control Solenoid 

The modern automatic transmission uses a combination of electronic components and hydraulic valves. The solenoid plays an important role in controlling the valve body. When it fails, you will get a P0700 code.

What are the Common Symptoms of P0700 Fault Code?

As it is the case with numerous other transmission issues, the P0700 symptoms aren’t unique to this code. Regardless, knowing what to look for will help you diagnose the root cause of a P0700. The most common causes are:

• Check engine light
• Transmission rattling noises
• Limp mode
• Incorrect gear selection or shifting

Check Engine Light

The check engine light is a quick signal that something is wrong with your vehicle. In modern vehicles, it can come with more information displayed on the dash screen. Regardless of your vehicle, the first step to fixing an issue is knowing it exists.

Transmission Rattling Noises

Rattling noises are never good, especially when they’re coming from the transmission. If you hear rattling or grinding noises, and all you’re reading is a P0700 error, there’s a decent chance that something has come loose in your transmission. Needless to say, this symptom is a clear sign that you need that get that car on a lift sooner rather than later. 

Limp Mode

Limp mode is a failsafe meant to protect the engine and vehicle’s occupants if a vital component fails. As transmission issues can be a safety hazard, the limp mode will activate when you have any serious transmission code like the P0700. The engine computer will limit the speed of the vehicle or gears that you can access.

Incorrect Gear Selection or Shifting

Your vehicle will go into limp mode before you experience this symptom. However, Experiencing sticky or incorrect shifts is one of the primary indicators of a P0700 trouble code. It even might not shift at all, which is a safety hazard.

How to Diagnose and Fix the Cause of P0700 Code 

Transmission issues can be scary. They are preventable with regular maintenance but often burn a hole in your pocket when they happen. Most transmission problems are possible to diagnose, even as a DIY mechanic. So, don’t panic!

OBD-II Reader

First, you need to connect your scan tool and run a full scan of the car. That way you’ll get the complete picture of what’s going on with your car. A standalone P0700 error and a P0700 error followed by two more transmission errors won’t point you in the same direction. Knowing exactly what you’re dealing with is a must for transmission issues as tinkering around the transmission can damage it further and will most likely waste time.

You’ll usually find the OBD-II port under the passenger side dash. Hook up your reader, run the scan and write down the codes.

Visual Inspection

Since a decent amount of TCM issues are caused by physical damage to the unit, it’s a good idea to take inventory of the undercarriage of your car. Look for any obvious signs of damage. Try to remember if you ran something over recently, that could have bounced off the road and caused any issues.

To access the transmission for inspection, you need to jack up your car on either stands or a lift. Look for breaks in the wiring harness, solenoid corrosion or external damage to the transmission. Transmission fluid in your driveway or a burned apple smell are additional signs of the P0700.

Dismantling the valve body should come last, as it is a time-consuming process. If you notice rattling while driving, it may not have a choice. 

Wiring Harness Test

This is a crucial step in determining the root cause of the P0700 code. Specifically, because the failures rarely come from the valve body, but the solenoid or wiring. 

Often there is no external damage to the wiring, but internal damage to the connector in the harness. First, your car needs to be in the “key on engine off” state. A multimeter is necessary to test the voltage coming from the battery and whether the right signal voltage is coming from the wire.

Now, back probe your wires at the connector. The positive (red) wire delivers power, ground (brown) prevents over current and signal (blue) returns a voltage reading to the engine computer. Probing the signal wire will give you around 5V and the live wire 12V.

Transmission Solenoid Test

The solenoid opens and closes valves based on the signal it receives from the engine computer. You can test the functionality of the solenoid using your OBD-II reader or a multimeter. It should remain in the closed position in neutral and open when changing to drive.

How to Fix a P0700 code

This depends on the root cause of the issue. If internal components of the valve body or TCM have failed, those parts need to be replaced as a whole.

Changing your transmission fluid is a great way of preventing transmission issues. You need to change your automatic transmission fluid around every 50,000 miles. Changing your ATF can also resolve a P0700 in some instances.

Tearing down your transmission is also a viable option if you have the tools and the know-how. Replacing the internal components is complex but is inexpensive compared to the costs and labor that a mechanic will charge.

Does P0700 Clear Itself?

In many modern vehicles, you need to clear the codes with an OBD-II reader before the powertrain control module disengages the limp mode. Depending on your vehicle, the P0700 code might clear itself within a drive cycle. Chances are, you don’t want to risk it in any way.

Is It OK to Drive with P0700?

First off, driving with a transmission issue is not an option. It is a safety hazard, as you can end in reverse when you select park, for example. It is unlikely that you will be able to drive with a P0700 code in any way, but you should avoid driving with this trouble code.

Fix the P0700 Code with Quality Parts!

Now that we have enlightened you about the world of the P0700 trouble code, it is time to address the root cause. Temporary fixes are great to get you back on the road, but more permanent ones are needed for this issue as soon as possible.

Here at eEuroparts.com, you will find all the permanent fixes that you need. Our comprehensive parts catalog and easy-to-use interface will help you find the exact components that you need. Just select your vehicle from the dropdown list and all the parts available for your vehicle will be ready for you.