How do I fix code P0685?
What repairs can fix the P0685 code?
- Repair of shorts or bad terminals or connections.
- Replacement of the powertrain control module relay.
- Underhood junction block replacement (fuse box)
- Replacement of battery cables and/or connectors.
- Fuse replacement.
What is a ECM PCM power relay?
The PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) comes with a power relay that provides battery voltage safely to the right PCM circuits. It’s a contact type relay activated with a signal wire from the ignition switch.
What is a power relay control circuit?
A power relay is a device that uses an electromagnet to open or close a circuit when the input (coil) is correctly excited. They provide a high level of isolation between the control signal (coil) and the output (contacts) – typically with a rated impulse voltage of 4 or 6kV.
Where is the ECM power relay?
engine main fuse relay control box
The relay is located in the engine main fuse relay control box. The defective ECM-power relay is removed from the control box by pulling it straight up and out of socket. The new ECM-power relay is installed into the socket and the engine scanned for codes.
What is the difference between a PCM and a ECM?
Most people, including automobile technicians, confuse the two for each other. The main difference between the two is that the ECM controls specific parts of the engine, regulating and sending commands. While the PCM is used in newer models to control almost all engine functions.
What happens when ECM goes bad?
A bad ECM may lead to a vehicle that won’t or is difficult to start. If the ECM fails completely, it will leave the vehicle without engine management control, and will not start or run as a result. The engine may still crank, but it will not be able to start without the vital inputs from the computer.