P0700: Transmission Control System (MIL Request)

Modern vehicles come equipped with automatic transmission systems that allow drivers to shift gears automatically.  Newer automatic transmissions have a transmission control module (TCM) that monitors the activity in the transmission and sends the data to the powertrain control module (PCM).

Code P0700 is a generic trouble code related to a fault in the transmission control system. This code will appear in the engine control module whenever the transmission control module is reporting a fault.

What Does the P0700 Code Mean?

Diagnostic trouble code (DTC) P0700 stands for “Transmission Control System (MIL Request).”

The TCM monitors the sensors and actuators in the transmission system and sends the data to the PCM. This module monitors the throttle speed sensor, motor speed sensor, and output shaft speed sensor. Once the module detects something wrong with the transmission controls, it’ll trigger the P0700 code.

The transmission control module and the engine control module are closely associated by default even though they’re separate modules. They usually communicate over a high speed CAN bus to expedite reaction time between the two modules. Transmission modules differ greatly between OEMs and platforms but they all have basically the same job.

Note that P0700 is a generic informational code. It doesn’t point to any specific fault in your engine. It only indicates that something is wrong with the transmission.

The code P0700 could be logged with other trouble codes, such as P0700, P0701, and P0702. They can cause drivability issues, so it’s best not to drive your vehicle once your OBD scan tool retrieves these codes.

A Note About the TCM

Let’s unravel some of the abbreviations. When the transmission controls are in a separate unit (TCM), the engine control module is referred to as an ECM rather than a PCM.

Older electronic transmissions were controlled by the same computer that controlled the fuel injection and ignition. That module was abbreviated “PCM,” which stands for “powertrain control module.”

Older electronic transmissions were controlled by the same computer that controlled the fuel injection and ignition. That module was abbreviated “PCM,” which stands for “powertrain control module.”

– Richard McCuistian, ASE Certified Master Automobile Technician

There were exceptions to TCM/ECM evolution. Jeeps as far back as 1987 had a separate transmission control module and Chryslers tended to separate the engine controls from the transmission controls on their platforms. However, many other platforms began putting the transmission controls and the engine controls in the same unit.

Of late, there are such intense electronics dedicated to engine controls that engineers just about always house the transmission controls in a separate unit.

That TCM is what this code is referring to.

Note: The definition of code P0700 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

What are the Common Causes of the P0700 Code?

• Low transmission fluid level
• Dirty transmission fluid
• Dirty or contaminated TCM
• Malfunctioning engine coolant sensor
• Slipping converter clutch
• Bad valve body
• Failing shift solenoids

What are the Common Symptoms of the P0700 Code?

• Illuminated check engine light
• Activated fail-safe mode
• Hesitation
• Problems changing gears
• Stalling and rough driving
• Decreased fuel economy

How to Diagnose the P0700 Code

Various makes and models can log P0700 because it’s a generic informational code. Its symptoms and causes could be similar across different vehicles, but that doesn’t mean there’s one diagnostic and repair procedure that would work for all.

Diagnosing this trouble code usually requires specific tools and an in-depth knowledge of the transmission control system. So if you don’t have the right equipment or aren’t familiar with the system, it’s best to go to a mechanic for a diagnosis.

How to Fix the P0700 Code

Fixing the P0700 code can be challenging. That’s why we recommend asking a trusted professional to fix this problem for you if you’re not a seasoned automotive DIYer.

But if you’re someone who’s knowledgeable about trouble codes and the transmission, you can address the issue. However, make sure that you read up and research the problem first before doing anything with your vehicle. Guides like those from Chilton or an ALLDATA subscription can be very helpful when fixing a P0700 code.