P0700: OBD-II code P0700 is a general MIL request from the TCM — the transmission control module has detected a fault and is asking the PCM to turn on the check engine light.

Symptoms

• Check engine light is on; the transmission may shift harshly, slip, or enter limp mode (typically stuck in 3rd or 4th gear).
• Delayed engagement into drive or reverse, harsh shifts, or the vehicle refusing to shift out of a specific gear.
• A stored companion code on the TCM will point to the actual root cause — P0700 alone tells you very little.

Common causes

• Any active transmission code on the TCM in the P07xx range — covering solenoids, sensors, gear ratios, or clutch faults.
• Low or contaminated transmission fluid affecting solenoid operation and clutch application.
• A CAN bus fault between the TCM and the PCM — usually paired with U-codes on both modules.

What to do?

Scan the TCM specifically — P0700 is a wrapper, and the real diagnostic information lives in the TCM's own stored codes. Check transmission fluid level and condition on vehicles with a dipstick. Address the specific TCM code first; P0700 clears automatically once the root cause is fixed.