Just driven the 945 down to Yorkshire and experienced a very strange fault.
The headlamp dip/main beam switch and headlamp flasher are on a stalk on the left of the steering wheel.
Whenever I click the stalk backwards to change the setting or flash the headlamps, the engine dies immediately. If moving along it starts again after a brief hiccup, but if stationary it will cut out, especially if the stalk is held back.

A mystery to me, any enlightenment welcome please!

Owen F

james sousa has the right answer. done this a few times over the years in the shop.

Hi,

I went out to each of you fellows posts on this thread, as there is a lot of heavy “Friday” thinking going on here!

Whew! Good thing there’s weekend following. He may be still be on his way back home to Scotland though?

Its going to take awhile and methodical testing one thing at a time to isolate the grounds down to the ONE and ONLY.
All of it makes sense, that this, is a weird problem!

Phil

Hi Phil,

It's a wiring puzzle where it doesn't blow fuses.
If Ian is a genuine Scotsman, perhaps he saved money and used a penny at
Fuse 18?

Have a great weekend, Bill

Hi everyone, 7am here in Yorkshire, travelling back North to Scotland today.
Thanks to everyone for all the help on this one - a lot for me to go through, and autoelectrics are definitely my weak area!
Must remember not to flash the headlamps on this trip.

Just for interest - it's a 1991 945, owned by me since 1995 and needed hardly any major work since then.Brakes all renewed and service items, but still on original clutch and major components.

OwenF. (aka IanF)

Back up to Scotland yesterday, fault still evident on the way back when I inadvertently flashed a signal on the motorway.
Tried again this morning and it cut the engine for a couple of pulls on the stalk, and then guess what- it started to work normally. The headlamp flasher could be used normally and the stalk could be used to switch from main beam to dipped beam normally. No effect on the engine at all.
Typical intermittent fault. I will now go over all the earthing points you guys have mentioned and make sure there are good contacts, then wait and see if the fault comes back.
Thanks for all the advice.

OwenF

Hi,

The ground wiring from left stalk (headlight flasher/dim switch) shares with the ECU's ground. Dismantle the cosmetic cover at the driver's footwell (this for UK cars) to see them. Clean them and see if it happens again.

Amarin

Thanks everyone for a great response. An earthing issue seems to be the main suspect and a good place to start.
It will have to wait until I am back up in Scotland, just remembering not to flash headlamps at anyone (and avoid night time driving)!


OwenF

Amarin's thought about a ground fault at the chassis ground tab behind the ECU is certainly food for more thought.

I'll start out by noting that fuses aren't being blown here so a 12V short directly to ground likely isn't happening. You also say this is a sudden stall out, so the odds of it being charging circuit related aren't overly high, but you have been recently working at the battery so that needs to be kept back of mind. Odds are now higher in my mind that it's a ground fault. Some component is likely getting it's path to ground not through its normal direct to chassis ground path (or only partially if it's corrosion) , but rather backfeeding through another circuit to ground. When the circuit gets activated it is no longer a good ground path and can cause all kinds of odd problems. As an example, when there's a ground fault at a taillight, something odd like touching the brakes when the turn signal is on might suddenly stop the flasher, but that's not the circuit we're interested in here at the moment.

As the headlights are involved here, the ground points at the headlight assemblies (one for each side) are known problem areas for ground faults and could be related to such back feeding when the headlights are on. It would then be something like one lamp beam circuit getting all or part of its ground through the other beam circuit. How that's actually causing your problems here I don't know, but because it's easy to check and a stalk switch related circuit then I'd begin there. Check the chassis ground terminals near the headlight assemblies under the hood latches (loosening/re-tightening just for the heck of it) as well as making sure the headlight connectors are solidly seated, including peeling back the boots and pushing the wires forward (another known problem area as I mentioned before).

Now going back to Amarin's thought: Looking at the GB (UK) headlight wiring diagram again, there is a ground wire directly from the stalk switch, but it's to the ground rail (31/31) underneath the relay tray. That ground rail is shared by all the relays, including the headlight system relays. There's then a ground wire from that rail over to the actual chassis ground (31/10) at the silver metal tab behind the ECU. With so many relays involved then all kinds of weird things could be happening if the ground fault is in that circuit. Now this is for a 1995 940, while I believe yours is a 1991 even though you don't list it in the heading. Normally for this kind of circuit I'd expect it to be consistent throughout the 940 series. In checking a late model 700 diagram just out of curiosity, again all headlight and stalk switch associated grounds go to under the relay tray. If Amarin has access to an early 940 Volvo Green Manual diagram then I'd be interested if it shows different.

Also, the ECU doesn't have it's ground connection at the ground tab (31/10) behind the ECU (as you might logically expect), but rather at the main engine ground point at the fuel rail (31/32) along with things like the AMM. That's another known problem area, so before going further, loosen, clean-up and re-tighten the ground terminals there. That also takes us back to making sure the engine ground from the intake manifold strut is good back to the battery (where you've been working). Hmmm, all the more reason Bill might be right and had it figured right from the beginning?

I shouldn't carry on here until you've checked those easy things out, but having my nose in the wiring diagrams once again then I will, assuming the stallout hasn't gone away.

Looking at it again from the problematic stalk switch, all other paths to ground go through the relays I mentioned and to the relay tray ground rail. Pulling the relays as I suggested one at a time would quickly isolate those ground circuits and might point to the errant ground path without having to start removing all kinds of things to get at other test points. So, step three here, go back and make sure you did as I previously suggested.

Failing all that, you'll need to start opening up things to do further checking, like cleaning up their grounds and doing voltage and resistance measurements between various points. It's a tough call what I'd do next, whether to open up the steering column to test at the stalk switch, or whether to pull the relay tray so you can flip it over to check the grounds and check for a melted socket and loose wires, or whether to take the side panel off to remove the ECU and check the chassis ground tab behind it. I'd say pulling the relay tray is next on your list in terms of known problem areas with high current circuits like headlights possibly causing socket connection and ground problems.

Keep us posted on your progress. We've given you a ton to think about and pursue, so try to go through them in logical order, turning every stone along the way.. I was just thinking that a typical soggy Scottish winter makes it ripe for aggravating ground connections at this timne of year.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Dear Dave,

Thank you for pointing these out. I may have mistaken here. Just because the ECU is pictured next to the grounding pegs in the wiring's book photo, doesn't mean its grounded there!

And I used a 1994 wiring book. Unfortunately I don't have 1991 book with auxiliary injector.

Yes ALL ECU grounds are at the intake manifold.

And I found out one more thing. The main fuel pump is grounded at behind ECU (ground labelled as 31/10). So pulling the stalk may have disrupted the fuel pump's operation. At least thats my hypothesis now.

I stand corrected. Thank you guys!

Amarin.

Hi Dave,

I finally got the wiring Greenbook for the 93 940 !
Let me know what pages you want and I'll send.

You're right that Both ECUs use only the Intake manifold grounds (2).

The right headlight shares a ground with the RSR coil.
Dunno if the the ground can fail to make enough voltage drop to the RSR
coil and let it fall out.
Maybe that ground is resistive?
That's behind the test with pulling the fuses. Diagnosing the fault.

As you said in the beginning it's a weird problem.

Bill

Hi Ian, or is it Owen?

Here's a quick test to narrow down the problem with your lights:
Remove fuses 17 & 18 (they are the high beam fuses)
Then see if flashing the high beam switch still croaks the engine.
Try with only Fuse 17. Then try with only Fuse 18.
See if the engine will flash high beams OK with only one headlight.

Post back

Bill

I had a similar problem in our 744 Ti - it stalled when I put the high beams on.

ITS IN THE FAQ!!!

Grounding problem in the left front fender.

The lights hog all the ground available cheating the ignition system.

I checked all the grounds and also cleaned the attachment of the antilock tower, as something is grounded to it.

I took a good look at the battery cables and found corrosion inside the battery end of the positive cable, some strands had rotted away. I cleaned and soldered the connection. The small wire just pulled off!

I also checked the engine to body grounds - as I remember there is one at the top of the engine and one at the bottom.

Hi Owen,

We discussed this a month ago.
It sounds like a problem with your battery cables.
Have you cleaned the battery and cable ends?
Carefully check the crimps for the smaller cable at the positive terminal for being loose or having a bad crimp, look for corrosion.
Is your battery dying from old age?
Is the alternator charging OK.

Bill

Thanks Bill. I fitted a new Bosch battery after the last problem with difficult starting when just warm (seems OK when fully cold engine or fully hot engine). We have concluded this was caused by the Cold start injector flooding the engine, most probably caused by the temperature sender for the ECU going out of spec. (Yet to be changed).

This new issue seems to be quite separate?

Owen F

Now that's a new one I've never heard of.

Along Bill's train of thought, hope you checked the battery ground connections at the nearby frame member and as well at the block. Loosen, clean if needed, De-oxit if you have it, and re-tighten. Double check that the battery clamps are well seated on the posts and properly tight -loosen, twist down, re-tighten. Inspect the battery cable clamps and all crimp connectors at the other end of both battery cables for signs of corrosion or broken strands. Are any of those cables or clamps aftermarket? You could measure voltages and voltage drops in the charging system, but I'd keep tend to skip that for now as you're symptoms are rather sudden.

If that doesn't make a major difference then you need to start thinking harder, like a possible short somewhere or a ground fault causing an alternate path to ground.

I'd start fault tracing from the errant stalk switch by isolating various parts of the circuit. I'm looking at the GB version of the 900 high and low beam circuits -should be the same or similar for all 900s.

Begin by pulling the headlight relay, relay tray, front row, second socket from the left. That eliminates any stray 12V getting from the battery to the bulb out sensor relay and beyond to the headlamps and their ground. It also eliminates any chance of 12V passing from the stalk switch to ground through the high beam relay to ground. Re-test for stalling. If that fixes it then that relay, the stalk switch and associated wiring goes on the chief suspect list and you begin further isolating from there.

If no change then with that relay re-installed, pull the high beam relay, front row, rightmost socket. That elimnates any voltage from battery +12V getting to the headlamps through fuses 17 & 18 and as well the high beam indicator on the dash. Re-test. If that fixes it then that relay and associated wiring, especially at the headlamp grounds and under the relay tray goes on the chief suspect list.

While we're on that part of the circuit, check the headlamp socket connectors. If they ever make poor contact then the contacts get hot and the plastic can melt, allowing the wires to pull out or short (I've had one such problem with headlamps occasionally going out). DRL means current is always passing through. Those connectors are an even bigger issue if high intensity lamps are used.

If neither makes a diff then the stalk switch goes on the suspect list and as well a possible ground fault some place in the engine management system.

Report back and we can take it from there.

A couple of questions:
o When you touch the stalk and stall out, is it a sudden stall or does it begin with a stumble or misfire?
o If only the park lights are on (headlight switch in the middle position) does that change things? I believe your DRL light switch is the same as mine and operates that way.
o Does the high beam dash indicator light at the same time?
o Does the intensity of dash lighting change (turn up on high when checking that)?
o With headlights on, does the intensity of the beam suddenly drop (go up against a wall)?
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

In a reply to Dave's question - the engine cuts out instantly as if the key had switched it off.
Not sure about the answers to the other questions - I can only say I didn't notice anything else at all. I don't want to mess with it whilst away from my garage - let sleeping dogs lie, as the saying goes.

OwenF