2000 S70 GLT only starts after the battery has been disconnected

[monty]

Do you suppose because it was disconnected for 7 weeks that it went into a mode different than a short-term power loss?

[monty]

Is there any possibility that because of the 7 weeks the car sat with the battery disconnected, it has gone into a mode different than a short term power outage?

[rspi]

Try driving it for more than 30 minutes to see if that fixes it...please.

[wizechatmgr]

Have we verified the coils are receiving both 5V (pulsed) and 12V constant when cranking? The 5V signal is supplied by ECU, 12V usually switched battery - possibly through a relay. I don't have the schematic handy for that vehicle. Often if the ECU is unhappy (immobilizer, sensors drastically out of range, other software fault) it will not supply the 5V pulsed signal and the coils will not fire. On the other hand, if you're missing the 12V side but not the 5V, then the ECU is fine and you could have a relay or switch with an intermittent issue on the 12v side - possibly a weak coil in a relay or bad contacts.

Usually the 12V will be the outermost pins and the 5v the inner pair.

[monty]

I checked for 12 volts at the coils today and found 12 volts with key on. I wasn't able to check for 5 volts while cranking as I was alone. After a reset the car runs fine with everything working.

[wizechatmgr]

I'd be willing to bet you aren't going to get the 5V signal from the ECU before the battery reset. The only question becomes - for which reason isn't it sending it?

A heavy truck shop that works on Volvos should have a scan tool that can interface with your Volvo if there isn't a car dealer nearby. Their interface is a bit different depending on the type and year of equipment but they should have the correct adapters on hand for their newer trucks.

I'd call these folks, ask them if they can scan the car, offer some $$$ and tell them you know it isn't a truck but you're in a jam. If they aren't buried in work, they will more likely than not oblige. You're going to need to make rather sure it is having the issue or has the code recorded before they scan it. I wouldn't shut if off after arriving until it is in whichever service bay they'd prefer.
https://beavertrucks.com/

[PeteB]

Would pulling fuses to see what part needs a reset rather than the battery disconnect
help to narrow it down?
I agree that some module is locking out probably having something to do with the immobilizer.

[wizechatmgr]

Would pulling fuses to see what part needs a reset rather than the battery disconnect
help to narrow it down?
I agree that some module is locking out probably having something to do with the immobilizer.

Could be worth a try... If only to rule other things out as it still provides more data. They could also try a different key just in case it is a specific key having a transponder issue. (I'd imagine this has already been done and ruled out.) I'd also suggest trying to start it with all doors, trunk and hood open in case we have a weird rogue short - it shouldn't make a darn bit of difference, but if it does, we know where to start. I also wonder if the factory radio has been replaced. Old VWs would have an issue where folks would end up tying the communications bus to ground because the diagrams weren't correct with aftermarket harnesses.

Using VIDA/DICE to find the previously stored or currently active factory codes that don't always illuminate the check engine light (most regular consumer OBDII scanners can't do this) would be a great idea but that isn't an option here.

Without verifying functionality of the new part and failure of the old part - it's a shot in the dark with complex control systems. Since it is prohibitively expensive to just swap say an ECU, you need to be able to verify the input, the detected/sensed input & intended output - if the input is correct (sensed within range) and the output is not, then the module is faulty. In order to verify the input sensed, you need to be able to pull stats to make sure that the signals are being correctly received by the ECU and all other modules and are within range. Or you can get the ECU cloned just to find out it wasn't the cause of a particular issue.

I much prefer the old days where everything was mechanical or electro-mechanical. Everything could be tested relatively easily and in most cases visually with cheap & basic tools. Heck, even the days of throttle body injection weren't too bad. Ah, the good old days...

[monty]

Update: took the car in to a shop that specializes in European vehicles. Fellow seemed to know his stuff, the kind that likes what he does and really wants to help someone who isn't a stranger to greasy hands! After driving the car in and shutting it off it was, of course, now in a crank-no spark condition. He connected a scanner and was unable to communicate with the ECM. At that point he said that would appear to indicate a grounding problem. He could access the ABS and see the left front sensor had registered a fault.

As an 18 year old rust belt car (that and Volvo's use of dissimilar metals) an open connection is a distinct possibility - now the hard part! I've got the wiring diagrams downloaded to my laptop and as soon as I get a grip on what they're showing me (they're unlike anything I've seen before) I'll start the search.

Wish me luck. . .

P.S. No charge for the scan!!!

[scot850]

Monty, I had an issue with the TCU on my current 'project' prior to buying it. I took it to the dealer as my Vida system would not communicate with the trans and the check lights were on for the trans and engine. They removed the TCU and ECU and carefully cleaned the contacts of both with a special 'Wurth' brand electrical contact cleaner and cotton buds as there was oxidation/corrosion on the contacts. They then re-fitted and removed the units a few times to help mechanically clean the contacts and then they were able to read the TCU and re-set the errors.

There are also multiple grounds in the engine bay, and even the positive cables can need cleaning or replacing.

Also check the B+ cable especially where it contacts in the main kidney shaped fuse box above the brake booster. If the nut and end contact are not shiny you may have to replace that wire.

Neil.