2004 XC70 no start - faulty fuel pump and/or electrical connections? Topic is solved

[enotslim]

Let's do this- let's locate the fuel pump relay ...

Thanks. This is the type of testing I am looking for. I will try this at the next opportunity. However, the main issue is the intermittent pattern of this failure. The car has been starting for the past four days. I can drive it but I don't want to stop the engine anywhere but in my driveway.

Any way to test when the car actually does start? The pump is getting 12V. Maybe a faulty ground would still be evident? The harness was degraded, presumably by rodents. I re-wrapped the harness but did not attempt to "fix" it because the car was starting at that point and the damage did not appear to be very deep. I was a little uneasy about this but I didn't want to cause more problems than I solved by fully exposing all the wires in the harness and damaging them further in the process.

I removed, tested and swapped the fuel pump relay previously when the car would not start. The relay seemed fine. I chose this relay as the third position right-to-left relay in the photo based on the info here ( (Photo is rotated 180 degrees - I can't get the photo to display without rotation.) I didn't see 30 and 87 in the layout on the relay (the same relay used at several positions in this car.) Will 30 and 87 be on the circuit board itself?

Does VIDA include this type of information about specific wiring of relay pins, etc.? Does that require the elusive electric circuit component of VIDA?

Can these types of things be investigated directly using VIDA/DICE without the need to jump relays, etc., as suggested here?

[jonesg]

You can pop the relay open and reflow the solder, heat cycling and vibration cracks the solder joints.

[enotslim]

You can pop the relay open and reflow the solder, heat cycling and vibration cracks the solder joints.

That's good to know. But the relay tested OK. Energizing 12V across leads 1/2 caused resistance across 3/5 to go from high to zero (and resistance across 3/4 to go from zero to high). Doesn't seem like the relay is at fault or like repair is necessary.

[Vova585]

I doubt that relay is at fault given intermittent issue of the problem. Plus we still don't know what is the reason that the car is not starting(lack of electricity vs failure of the pump being our primary suspects). I don't know of any way to diagnose the car when it is running perfect. Even dealer will likely charge 1h worth of labor trying to recreate the problem,but at the end of it we say "come back when the problem will be present".
In regards to the relay. Based on the picture terminal 1 and terminal 2 are the control of the relay. Meaning when you command the car to start(key position 2 or 3) it will be energized and cause table to switch to terminal 5. So following previous post, terminal 3 can be translated as (31) and terminal 5 as (87). You can use continuity function of multimeter and confirm my proposal by trying to test between terminal 5 and unplugged fuel pump terminal .
In regards to faulty ground terminal-you need good ground as much as good positive. You can possibly try to check the resistance between negative post of the battery and negative terminal of the fuel pump connector. Then try to move the wiring a little to see if the connection is lost which would indicate damaged wire.

[Vova585]

If you are searching for a great resource an vida alternative:
https://www.alldata.com/diy-us/en/diy-r ... n5EALw_wcB

[abscate]

I think you will have to bite the bullet and open that harness. Rodents will chew the insulation and even the metal of wiring. Moms Golf had steering angle sensing chewed right through

[Vova585]

I think you will have to bite the bullet and open that harness. Rodents will chew the insulation and even the metal of wiring. Moms Golf had steering angle sensing chewed right through

I totally agree with above statement. However I would opt not to repair the old one. I would try one of 3 options: 1) go to the dealer and ask them how much that harness cost. If the price is around 100 for a piece of mind, I would buy. 2) go to a local salvage jard that is known to have volvos and cut a long piece of that harness and them use the https://www.amazon.com/Connectors-Haiss ... 5303&psc=1
To connect them together. 3) if no time to go to salvage yard,contact erievovo and they will send you correct part for a reasonable price.
Why would I not try to fix old? Fixing old stuff might take more time than to replace with good used or better new, unless you are opening all the harness and inspect all wires you never can be sure that there is no damage to the wire isolation etc...Long story short I think it is a great fire hazard to drive with those wires.
Good luck with your repair.

[enotslim]

Wires within the harness to the fuel pump appear to be intact at both of the sites where the protective coverage is damaged by presumed rodent activity. See photos. I looked much more closely but am not showing every image here. I cleaned the surfaces of the insulation of the inner wires. I did not find any signs of damage or even wear with the exception of some very slight surface roughening of the insulation of one wire that seems to be evidence that it spent the past 19 years kissing its neighbor. I don’t think this harness shows physical signs suggesting that it is likely to be malfunctioning.

I was surprised to find that this “harness" is nothing more than coupled wires manipulated to conform to a particular pathway within the vehicle, wrapped at minimal coverage with what appears to be standard electrical tape and soldered to appropriate fittings. I can do that (although I don’t want to). The wires at the "supply" end of this particular harness disappear to find unknown fates elsewhere so it isn’t quite that simple but … Removing the cover from the entire harness and inspecting the entire length of the inner wires would actually be pretty easy, but does not seem justified given no evidence of damage to the covering except at the two spots already examined. Agree/disagree?

Voltage across the larger caliber leads (black and blue in the photo here) spikes for less than one second to 11.8 V when the key is moved from position 2 to position 3. Voltage then decreases to zero, or to only a few millivolts. Voltage across one other pair of leads tested does not change much or at all. Didn’t test anything else today due to time constraints but I can do more if useful. Like verifying ground from the harness to the battery by continuity.

Should voltage remain at 12V longer? Perhaps if the entire circuit is intact? Rapid shutoff could be a safety feature to minimize the risk of igniting fuel in the tank if the pump is shorting out, etc.? Or does this mean that something upstream actually is failing to deliver 12V long enough to activate the fuel pump under all circumstances, and that sometimes this tips into a failure-to-start behavior?

Of course, the car starts now so the pump obviously receives 12V long enough to start the car. Now. I can repeat this testing if/when the car does not start. (Any problem driving with the rear seat out of the car to facilitate testing when start fails? After reinstalling the seat I am able clear the airbag code.) But lack of physical damage to the harness points to direct pump failure, I think. Is it possible that accumulated debris within the pump housing/mechanism is intermittently blocking the impeller, and can be removed after disassembly? I have everything necessary to replace the pump (except an actual new pump) so I can take a look at this possibility and go from there. Ccan’t get a new pump (from fcp or similar, not
Amazon or similar) until next week anyway and I think disassembly is required for repair or replacement.

[Vova585]

Hard to tell at this time what is going on. Let's hope aisin(toyota) made transmission and water pump started to finally exhibit its magic and the car "fixed" itself.
It is totally normal that you are only seeing 12v for 1sec upon changing the key from position 2 to 3. It can be viewed as "priming" stage to bring the fuel pressure back to necessary starting value. At this point I would carefully wrap all wires in electric tape and maybe add protective corrugated plastic sleeve with addition of curse towards all rodents. You sure can open the tank and inspect what is going on with protective screen/mesh at the bottom of the tank. If it is too dirty you can go to harbor freight and buy yourself an ultrasonic cleaner($60-80) couple drops of dawn soap and 20minutes of magic and your screen is clean again. (Then you can clean the ultrasonic cleaner and present it to your significant other as a present to clean their jewelry, will work nicely as well). I would also remove the actual pump from the housing and inspect fuel intake port(sometimes they have a mesh which needs to be cleaned,but rare unless you were extremely unlucky at the gasstation. But it is totally up to you if you want to play with it. You also can obtain a spare plug/harness from the donor car and use it to create emergency "defibrillator"(pardon my comparison) meaning just attach 2 nice long wires to that spare plug so in case something-you have opportunity to connect it to pump and then to battery and you are good to drive home(your car is without PEM so it will not effect your fuel pressure negatively). With gas tank being sealed you don't have to worry about any small sparks at battery site upon initial connection(would be similar to connecting main cables)
Fingers crossed your issues are fixed.

[abscate]

Your wiring looks good, I agree that’s rodent insulation only damage and can be taped.

The fuel pump relay function is complex and not just a classic relay. It runs for a second or two on start signal then needs a 40Hz? Ac signal to stay running. It’s possible it’s failing in mode 2 although that shouldn’t inhibit start. The only way to catch that is to monitor fuel pressure during the no start condition