P0700 — Transmission Control System Malfunction (MIL Request)

What it means

This is not a fault of its own but a request sent by the transmission control module over the data bus, asking the engine module to light the check engine lamp. The real fault is stored inside the TCM, so the gearbox memory must be read with a scan tool that supports the transmission controller. In most cases the automatic transmission has already switched to limp mode with one fixed gear and no torque converter lockup.

Likely causes (most common first)

1. A stored fault in the transmission control module: solenoid, speed sensor or gear ratio code
2. Low, burnt or wrong specification transmission fluid
3. Worn clutch packs, valve body or torque converter causing slip
4. Damaged wiring or connector at the transmission, especially the internal harness plug
5. Faulty shift or pressure control solenoid
6. Failure of the transmission control module itself

Can you drive with it?

You can drive gently to a workshop, but expect limp mode with one gear; continued driving on a slipping gearbox destroys it.