Power Sustain Relay (PSR)

WARNING: This page is about a different car, the 2007 Mercury Mariner and 2007 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.

The PSR is wired in parallel with the electronic engine control (EEC) power relay. The PCM and the TCM use the PSR to keep the modules powered. The PCM and TCM must be powered to complete the normal power down sequence, after the key is turned to the OFF or ACCS position. For additional information on normal power down sequence, refer to HYBRID ELECTRIC CONTROL SOFTWARE . When the key is cycled from the OFF to ON or the ON/START position, the PCM smart driver grounds the PSR circuit. The PSR coil is energized and it closes the contacts of the PSR supplying the modules with the B+ power. The PSR coil stays energized after the key is turned to the OFF or the ACCS position until normal power down sequence is successfully completed. The PCM monitors the PSR output for an open and short circuit condition. The PSR circuit short to ground condition keeps the modules powered at all times and it may cause an excessive key off load on the low voltage system.

NOTE: The injectors and ignition coils are powered through a dedicated coil/injector relay so that the engine stops running when the key is turned to the OFF position.