P0888 – Transmission Relay Always Off

P0888 Possible Symptoms

Engine Light ON (or Service Engine Soon Warning Light)

P0888 Possible Causes

Transmission Control Relay harness is open or shorted,Transmission Control Relay circuit poor electrical connection,Faulty Transmission Control Relay

P0888 Description

The transmission control relay is used to supply power to the solenoid pack when the transmission is in normal operating mode. When the relay is off, no power is supplied to the solenoid pack and the transmission is in Limp-in mode. The relay output is fed back to the Powertrain Control Module (PCM). It is referred to as the Transmission Control Relay Output circuit or switched battery. After a controller reset (ignition key turned to the run position or after cranking engine), the controller energizes the relay. Prior to this the PCM verifies that the contacts are open by checking for no voltage at the switched battery terminals. After the relay is energized, the PCM monitors the terminals to verify that the voltage is greater than 3 volts.