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Hesitation and hard starting issues solved - 2005 V70 2.5T - external PEM module Topic is solved

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Hesitation and hard starting issues solved - 2005 V70 2.5T - external PEM module  Topic is solved

Post by don_moore_1904 »

My car has about 100K miles and has been very reliable. A month ago, I suddenly had some hesitation at highway speeds when going straight and level. This first seemed like a auto transmission issue to me. After a few weeks, where there were some additional issues at lower speeds (always when the car had been running 1/2 hr+). Then occasional cold start long cranking. Luckily, codes P0190 and P0193 were tossed, and on another occasion P0190 and P0188. I found that FPS (fuel rail pressure sensor) and the PEM (fuel control module) experience common failures. The P0193 code is resistance out of range, so I (incorrectly) assumed my sensor was bad as others have found.

Furthermore, I found that the PEM module was outside on certain models and years, and Volvo moved inside when it was found they were failing at a high rate. On my car, the PEM is located on the side of the fuel tank, just inboard of the right rear passenger door - next to the fuel filter. To move it inside, there is a wiring harness PN #30798596 for 2005-2006 V70s and XC70s and 2004-2006 S60s, and a different PN #30798698 for 2004 V70R and S60R only. Basically, you cut the existing harness under the hatch of the fuel pump (under the right rear seat), and yank out the stub of the harness that went down to the PEM.

The new harness in a V70 routes to the rear of the car, and the PEM is mounted in the spare tire well. There is a Volvo service bulletin on that covers several models at https://askatech.com/AskATechLive/forum ... hx?a=13208

My PEM module had a distinct rattle like sand was inside, which turned out to be a large amount of oxidation on the interior surface of the heatsink. The 5-pin connector is located at the bottom of the module as mounted, so the particles of oxidation would sit across the pins. The oxidation was also adjacent to entire rear side of the circuit board. My belief after purchasing a new PEM and moving to the inside of the car is that my FPS is actually OK.

The job was fairly quick. You have to search around for YT videos that show how to get to the fuel pump. The right rear seat has to be removed, and there is an SRS connector so make sure to disconnect the battery first. Pull the bolster between the seat back and the door frame to access the seat back mounting bolt. Remove two bolts (17mm and 14mm) and one nut (15mm) under the seat back to remove the child seat mount and safety belts. Remove the ORANGE SRS connector and then under that the 14mm bolt that holds the right end of the seat back. There are two stretch bands that clip to 1/2" diameter rings underneath - unsnap them. The seat back then pulls towards the right side of the car and out. The rear compartment side panels do not need to be removed - just remove the bottom hatch covers. Then peel back and forward the material underneath where the seat back was, and the fuel pump hatch is visible. Remove the four 10mm nuts and carefully remove the cover, making sure not to damage the rubber gasket underneath.

The process is, compare your new harness connectors to those in the car (one on fuel pump, on on right body rail, and the one for the PEM). You will remove the first two connectors of the existing harness, take a deep breath and cut the harness right above the fuel pump where is continues down the side of the fuel tank to the existing location of the PEM.

There are plenty of good used PEM modules available on Ebay, because Volvo moved these modules inside after only a few years. The one I bought for $40 looks brand new, compared with the sorry state of my current one. Plug and play - no reprogramming needed. For me, this appears to have solved my problems. The transmissions are known to be a weak link on these cars, and I am grateful it was a far cheaper repair.

The light gray looking area at the bottom of the module in the first picture looks flat but is a heap of powdered material that resulted from oxidation in the old PEM module. It measures about 2M ohm to 5M ohm if you put DVM probes into it.
PEM_corrosion2.jpg (552.19 KiB) Viewed 343 times
PEM_corrosion.jpg (503.08 KiB) Viewed 343 times
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Re: Hesitation and hard starting issues solved - 2005 V70 2.5T - external PEM module

Post by abscate »

Exactly on cue for time and miles when my 2005 V70 PEM did the same thing. Thanks for an informative post

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