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DIY: 1998 Volvo V70 Fuel System Troubleshooting Tips

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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DIY: 1998 Volvo V70 Fuel System Troubleshooting Tips

Post by cn90 »

DIY: 1998 Volvo V70 Fuel System Troubleshooting Tips

* No-start is a very frustrating problem for car owners, so download these diagrams (and a jumper wire) and keep them in your glove box. Reading electrical diagram can be confusing, but no worry, I will make Fuel System trouble-shooting painless for all of you. Make sure you read the “Summary” at the end for a simple guide.

* If every 10yr/150K (“big if”), you preventively replace the Fuel Pump ($90 for Bosch) and the Fuel Relay ($45 for Volvo), no need to read further LOL...

* However if you have a “no-start” problem and no DTC (Diagnostic Trouble Code) on code scanner, then you want to rule out a Fuel System problem before dwelling into complex electronic troubleshooting (sensors etc.) saga.

* Here is a Simple Guide to trouble-shoot the Fuel System:

1. Make sure battery is fully charged.

2. Make sure your fuel is not contaminated and you have at least ¼ tank of gasoline.

3. Make sure you download appropriate car electrical diagram from forum. For my 1998 V70, I find that the most useful pages are: 4-11 and 92-93! Electrical diagrams are below:

4. However, I can tell you that for 1993-2000 model years (850, S/V70 series), the Fuel System circuits are very similar with 1 notable exception:
* 1993-1997 850 series ---> 15A Fuse #2 (same compartment as “Central Electrical Unit”)
* 1998-2000 S/V70 series ---> 20A Fuse #3 (same compartment as the “MAIN Fuse Box” near suspension tower)

5. Except for Starter Motor, all other electrical supplies go through:
B+ cable ---> “MAIN Fuse Box” ---> “Central Electrical Unit” ---> the rest of the car. So it is important to check the B+ cable, see below link.

6. Review Bosch Relays definition for “primary circuit” and “secondary circuit”.
For 85-86-30-87 relay type: 85-86 is the “primary circuit” and 30-87 is “secondary circuit”.
For 31-31b-15-87 relay type (fuel pump): 31-31b is the “primary circuit” and 15-87 is “secondary circuit”.

Relevant Readings:

* Fuel Relay Fix by Ozark Lee (using inexpensive capacitors from Radio Shack):
http://www.matthewsvolvosite.com/forums ... php?t=9681

* B+ Terminal repair by “DGM”:
http://www.matthewsvolvosite.com/forums ... hp?t=35208


1. Digital Multimeter: make sure you understand how to test Voltage (Voltmeter) vs Resistance (Ohmmeter).

2. Jumper Wire with Fuse ($2 at autoparts store).

3. Torx #25 key, if you are stuck somewhere and don’t have the T25 key, no worry, a small flat screwdriver will do it.

4. Long screwdriver to be used as “stethoscope”.

5. Small screwdriver for Schrader Valve. The proper way to test for Fuel Pressure is with a Fuel Gauge. However, you can do the ghetto test: press on the Schrader Valve Center pin (very much like a Tire Valve Stem), have a rag ready to capture fuel!

VolvoFuelSystem02.JPG (140.12 KiB) Viewed 13690 times
VolvoFuelSystem03.JPG (88.54 KiB) Viewed 13690 times


1. Review my simplified diagram. Note that key needs to be in Position II for testing.

In a nutshell, current flows from Battery ---> Big “11A” Fuses (50A and 60A types) ---> Main Relay FI System (2/32) ---> “11B/3” (Or Fuse #3) ---> to Fuel Relay (aka 2/23 or Fuse 103) where current flows from #15 to #87, supplying the Fuel Pump. Once you understand this current flow diagram, the rest is easy!


* Note when Main Relay FI System (2/32) is removed, I cut off supply to Fuse #3.

VolvoFuelSystem05.JPG (117.24 KiB) Viewed 13690 times

2. In the real world, this is where all the relays/fuses are:

VolvoFuelSystem04.JPG (149.34 KiB) Viewed 13690 times

3. To check if Fuel Pump is running or not:

* Key in Position II

* Place a screw driver on the Fuel Pipe as “stethoscope” and listen to a hum. Contrary to popular belief that the Fuel Pump is energized for only a few seconds when key is in Position II, I found out that as long as key is in Position II, the Fuel Pump runs. Check it for yourself.

Now, let’s have some fun…
4. Now look at Fuel Relay Socket (not the Relay, but rather the Socket itself):
* 31 = Ground
* 31b = controlled by the ECU
* 15 = from Main Relay and Fuse #3
* 87 = this goes to Fuel Pump.

5. Fuel Pump winding has a resistance of about 1.0-1.5 Ohms. Mine was 1.0 Ohms (measured via 31 and 87 on the socket).

VolvoFuelSystem06.JPG (142.4 KiB) Viewed 13690 times

6. When jumping terminals 15 and 87, the car will run just fine. The idea of the Fuel Pump Relay is when you have a car accident, the ECU shuts off fuel to prevent fire for the occupants. So if you do the ghetto fix (jumper wire between terminals 15 and 87), do it only as temp fix until you replace/repair the Fuel Pump Relay.
That is all folks, it is not that hard if you take your time to study the schematic of the Fuel System!

In Summary:

* To quickly rule out Fuel Pump issue, Key in Position II (don’t start the engine), place screw driver at Fuel Pipe and listen for humming noise. If there is noise, then your Fuel Pump is likely OK (actually the proper way is to hook up a pressure gauge to the Schrader valve and measure the psi).

* If no FP noise, then either the Fuse #3 is blown (For 850 series Fuse #2), or Fuel Relay is bad, or Fuel Pump is bad.

* Place a Jumper in 15 and 87, give it a good crank (sometimes fuel pressure drops to zero after an engine stall, so you need to give it a long ? 10-sec crank to build the pressure back up). If engine runs then Fuel Relay is bad. If engine does not start, then Fuel Pump probably went to heaven.

* This is how to install a jumper between 15 and 87:

2004 V70 2.5T 100K+
2005 XC90 2.5T 110K+
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Re: DIY: 1998 Volvo V70 Fuel System Troubleshooting Tips

Post by djohnk »

Smart move putting a fuse on the jumper wire between 15 and 87. When I was checking my fuel pump I just used a paper clip and so much current was going through the paper clip it heated up and gave me blisters on my fingers when I removed it. I now know the fuel pump is bad, but hope I didn't damage the wiring with that paper clip ... could have melted insulation somewhere.
1998 V70XC
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Re: DIY: 1998 Volvo V70 Fuel System Troubleshooting Tips

Post by jackmac94 »

Awesome write up. I'm resolving issues of my own with the help of Ozark Lee but this looks like a DIY that may help me down the line. Thanks!
1995 Volvo 850 GLT Wagon
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Re: DIY: 1998 Volvo V70 Fuel System Troubleshooting Tips

Post by farmshop »

Can I hot wire the fuel pump with a momentary 12 v supply to "load" the rail before starting?
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Re: DIY: 1998 Volvo V70 Fuel System Troubleshooting Tips

Post by luckykolo »

Anyone has tried to inspect the Central Electric Unit for corrosion? I am interested in inspecting contentions underneath the unit marked with purple color. Any tricks to it, or it's just about unscrewing it and lifting? Thanks
fuse box volvo.png
fuse box volvo.png (622.17 KiB) Viewed 347 times
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