Just want to post this as feedback, in case it will help somebody experiencing the S40 going into "low power" or "limp home" mode. The control unit will drop the engine into "low power" mode for a number of reasons, all relating to a bad sensor input indicating that the engine is not getting what it needs, or not operating correctly. Example: If the car gets a low fuel pressure signal from the fuel pressure sensor, it will drop it to low power mode. You will not necessarily get a trouble code, which leaves you guessing. This was the case with my s40. I first suspected (with 140,000 miles) that the in-tank fuel filter could be restricting fuel flow, or the fuel pump could be bad, or the fuel pressure sensor could be bad. Easiest first: change the fuel pressure sensor (easy, its up front on the fuel rail). Drive the car...runs fine for about 30 minutes, then ask for a lot of fuel, and drops into low power mode. This (with the sensor brand new and eliminated), is a good indication that the sensor is detecting a restricted amount of fuel. Time to change the fuel pump/filter assembly (which happens to be located in the tank). So, kind of a big job dropping the tank, clean out the tank (sediment...) install new pump/filter, install new tank cover seal, and problem solved. Just a note: this car (2004.5 S40 T5) required changing a pump wiring harness to work with the "updated" fuel pump/filter assembly. The pump, apparently had some reliability problems and an updated Bosch unit was specified (old model not available). Hope this helps somebody!

 

Thumbs up. Thanks for the feedback.