P0700: Transmission Control System (MIL Request)
The transmission computer has found a problem and asked the engine computer to turn on the check engine light.
What P0700 means
Many vehicles have a separate transmission control module that runs the automatic transmission. When it finds a fault, it cannot turn on the check engine light by itself, so it sends a request to the engine computer. P0700 is that request. It tells you a transmission problem exists, but not what it is. The real detail sits in another code stored in the transmission computer, which some basic code readers cannot see. KBB warns that P0700 can mean the car cannot change gears properly, which makes it dangerous to drive. Often the transmission enters limp mode, holding one gear to protect itself. Common underlying causes include low or burnt fluid, failed solenoids, speed or range sensor problems and wiring faults at the transmission connector. Shops use a scan tool that can talk to the transmission computer, read the specific code, check fluid level and condition, and test the circuit for the part named. Diagnosing the specific code first prevents expensive guesses.
Common symptoms
- Check engine light on
- Harsh, delayed or erratic shifting
- Transmission stuck in one gear (limp mode)
- Slipping
- Worse fuel economy
Most common causes
- A separate transmission fault code stored in the transmission computer
- Low or burnt transmission fluid
- Failed shift solenoid or pressure control solenoid
- Faulty transmission speed or range sensor
- Wiring or connector problem at the transmission
- Transmission control module fault
What to check yourself first
Check the transmission fluid level and condition if your car has a dipstick; fluid should be red or pink, not dark brown with a burnt smell. Have a shop or parts store read the transmission codes, since P0700 itself only says a transmission code exists. Note when the shifting problem happens, such as cold, hot or at a certain speed.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Transmission diagnosis with a full scan | $125-$183 | A transmission scan reads the codes stored in the transmission computer, which a basic reader may miss. |
| Transmission fluid change | $294-$356 | Low or burnt fluid causes many transmission codes. Check the correct fluid type for your transmission. |
| Transmission filter and fluid service | $621-$785 | On transmissions with a serviceable filter, often done along with solenoid work. |
| Replace transmission control module | $929-$1,006 | Only if the transmission computer itself is at fault. |
| Replace transmission (if internally damaged) | $6,238-$6,764 | If internal damage is found, a rebuilt or replacement unit may be needed. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0705 Transmission Range Sensor "A" Circuit (PRNDL Input)
- P0715 Input/Turbine Speed Sensor "A" Circuit
- P0730 Incorrect Gear Ratio
- P0750 Shift Solenoid "A"
- P0741 Torque Converter Clutch Circuit Performance/Stuck Off