Fuel pump relay failures are a common and frustrating occurrence with the Volvo 850. A failure effectively immobilizes the car and many owners, myself included, carry a spare relay in the car so as to not get stuck on the road miles away from any Volvo dealer. The relays are unique to Volvo and cannot be purchased from a standard auto parts store.
The signs of a bad relay vary but a failing relay will often emit a "buzzing" sound as it chatters.
Once the fuel pump relay has been diagnosed as the problem with the car it must first be removed from the upper electrical center. On North American cars it located under the fuse panel cover, under the hood, on the drivers side of the car. Access to the relay is achieved by removing the four T-25 torx head screws and lifting the cover panel off of the electrical center.
Upper electrical center.
Upper electrical center with the panel removed.
The fuel pump relay is relay 103. I have trouble getting my fingers around the pump relay to extract without first removing the 101/102 relay combo.
Once the relay is removed it is possible to actually repair the relay. Credit to Guy200 who first pointed out his successful relay repair.
The first step in the repair process is to remove the relay cap. This can be accomplished by carefully prying outward on the base of the cap with a pair of small screwdrivers on the sides that are adjacent to the labeled side of the relay. The cap has no real give to it so it is necessary to pry both sides at the same time.
Prying off the relay cap.
Once the cap is removed a small printed circuit board and the relay itself is revealed. Check for any obvious signs of bad things such as burned components, pitted or burned contacts on the relay, or loose solder joints. Assuming you find no obvious signs of damage the repair from here is to identify the two electrolytic capacitors. On my relay (898769000) the two capacitors were 100 µF and 22 µF respectively. The 898797000 relay may have different value capacitors.
The suspect electrolytic capacitors.
Although not exact replacements I was able to locate suitable replacements at Radio Shack, exact replacements can be procured from either on line parts houses or a good electronics supply house. The Radio shack replacements carry the part numbers 272-1028 for the 100 µF and 272-1026 for the 22 µF. The Radio Shack replacements are both rated at 35 Volts which exceeds the voltage rating of the originals. The 22 µF replacement is exactly the same size as the original but the 100 µF Radio Shack replacement is slightly shorter and it has a slightly larger diameter than the original.
Size Comparison between the original and replacement capacitors.
Electrolytic capacitors, almost always, are polarized so be sure to note the polarity of the capacitors before removing them. My relay had the negative side of the capacitor oriented to the top of the PC Board and the positive side oriented to the base side of the relay.
Removing the capacitors requires unsoldering four solder joints on the bottom of the PC board as shown in red circles below.
Capacitor solder joints.
There are a couple of acceptable methods for unsoldering the joints. One method is to use a solder wick and the other is to use a solder sucker. I used a wick and still had difficulty getting the old capacitors out since the PC board is double sided and has the solder connection on both the top and the bottom. A solder sucker might actually be preferable. Get the joint good and hot but not so hot that the PC board gets damaged.
Unsoldering the capacitors.
Once you get the capacitors out check the lead holes to assure that they are open and not blocked with residual solder. If they are blocked they can be opened with the solder wick or the solder sucker.
From here it is a matter of installing the new capacitors. The originals capacitors were mounted so that the base of both components sat nearly flush with the PC board. Since the Radio Shack replacements are not the same size, and further so that I could assure that solder flowed to the upper PC board, I installed them so that there was about a 1/16 inch gap from the circuit board to the bottom of the capacitors. Double check your polarity as you are installing the new parts.
The replacement capacitors installed into the PC board.
Once the replacement capacitors are installed in the PC board it is simply a matter of resoldering the joints and trimming the excess lead length with wire cutters. Use a generous amount of solder and hold the heat on the joint for an extra couple of seconds to assure that the solder flows to the component side of the circuit board.
The last step is to reinstall the cap. The PC board rides between two grooves that are molded into the cap itself so be sure to align the PC board with those groves while sliding it back together.
The relay can now be reinstalled in the car and tested.
The relay I repaired here was one that croaked on me a month or so ago. I put it back in the car and it works perfectly. The total cost was $2.67 at Radio Shack.
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