how to diagnose a P0700 code in my Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Tools Required: OBD-II scanner, multimeter, basic hand tools (socket set, screwdrivers), transmission fluid.
• Ensure the vehicle is parked on a level surface and the engine is cool. Disconnect the battery to prevent any electrical shorts while working.

2. Address Transmission Fluid Issues

• Sub-steps:
  1. Remove the transmission dipstick and check the fluid level; add fluid if low.
  2. If the fluid is dirty (dark or has a burnt smell), drain the transmission fluid.
  3. Replace the transmission fluid with the manufacturer-recommended type (typically ATF WS for Toyota).
  4. Recheck the fluid level after filling and run the engine to circulate the fluid.

3. Inspect and Repair Wiring

• Sub-steps:
  1. Visually inspect the wiring harness and connectors to the TCM for frays, cuts, or corrosion.
  2. Use a multimeter to check the continuity of the wiring. Repair or replace any damaged wiring as necessary.
  3. Ensure all connectors are seated properly and free of corrosion.

4. Test and Replace TCM (if necessary)

• Sub-steps:
  1. Reconnect the battery and use the OBD-II scanner to clear the P0700 code.
  2. If the code reappears, remove the TCM according to the service manual (typically involves unbolting and disconnecting wiring).
  3. Replace the TCM with a new unit, ensuring compatibility with the vehicle's VIN.
  4. Reconnect all components and clear the codes again.