P0700 fault code: transmission computer reports a fault
Plain-language definition
Transmission Control System (MIL Request)
What does it mean?
On cars with automatic and dual-clutch transmissions, the transmission is controlled by a separate control unit, the transmission computer (TCM). On its own, P0700 doesn't say what the fault is: it shows that the transmission computer has stored a fault in its own memory and has therefore asked the engine computer to turn on the check engine light.
The codes that describe the actual fault are stored separately in the transmission computer's memory; they may relate to gears, pressure, sensors or solenoid valves. P0700 acts like a messenger for these codes; its cause and seriousness depend on the actual code.
You may notice harsh or delayed gear shifts, the transmission staying in a single gear (limp mode), the transmission warning light coming on or a feeling of slipping. The symptoms depend on the actual fault stored in the transmission computer; sometimes there may be no symptom other than the light.
How serious is it?
This is a Priority code: the transmission computer has stored a fault and, on many cars, may switch to limp mode to protect the transmission. What the actual fault is can be seen from the transmission computer's own codes; it's important to look at them early.
Severity is a guide; if the warning light is flashing or you notice symptoms while driving, have the car checked at a workshop.
Common general causes
- Transmission fluid that's low, old or the wrong type
- Faulty solenoid valves in the transmission (shift or pressure valves)
- A problem with the speed or temperature sensors inside the transmission
- A problem with the transmission computer's connector, wiring or power supply (including low battery voltage)
- Less often, a fault in the transmission computer (mechatronic unit) or in the transmission's mechanical parts
The list shows general causes; a workshop finds the actual cause on your car with a check.
Definitions by make
Some manufacturers record the same code under their own wording:
- Isuzu
- Transmission control system signal error
How does it appear in the 2dakika report?
Transmission Control System (MIL Request)
If the code is read as a confirmed (stored) fault, the report shows it with the "Priority" severity; in pending or past records, codes that don't request the warning light and aren't critical appear as "Info". If the engine computer stored them, the conditions when the fault was recorded (engine temperature, rpm, speed) are shown too.
Read this code with the OBD-X1, and clear it from the app after the repair.
Clearing the code doesn't fix the fault; if the problem persists, the code comes back.