1994 940. Would it make sense to preventatively purchase and replace the original ECU? Various places, like Programa, sell remanufactured ECU's. Anybody try one? Anybody have their ECU fail? I have heard that such a failure is rare, but I still get nervous at the idea of original 28-year-old electronics....

Thanks.

As far as difficulty removing the ECU - in my 740. I pulled the ECU out to have more room to replace my heater fan.

Removal was really simple - You might wrap a towel around it ti protect the contacts from static electricity - probably NOT an iossue.

Dear james_a_sousa,

Hope you're well and stay so. I also hope New Year has started well and only improves!

Before accessing the Engine Control Unit (ECU), disconnect the negative battery cable clamp from the negative battery terminal. This cuts power to the ECU before the connector is removed from the ECU.

As to pre-emptive replacement, I'd have on hand one or two "known good" units. So, when the car runs smoothly, swap in the potential replacements, and drive for a day or two. If the car runs smoothly, note on the in-swapped unit: Good as of [date]. Store in a cool, dry place.

Hope this helps.

Yours faithfully,

Spook

I pulled the one from my 88 van and i was a bosche unit very similar.

I opened it and there are 3 16V caps you can check yours, look for black vertically mounted cylindrical aluminum cans.

buy new caps, they are about 50 cents apiece or so, cheap.


don't remove the board from its case or disturb the conductive paste from the heat sink.

look for a like , looks like an arrow often sort of a broken line on the cap. note that is your negative lead, take a pic so you dont screw up orientation as polarity does matter with electrolytic caps.

clip the can about 1/8" from the board try to leave little wires poking up, the leads from within the can. you just need little stubs.

at a proper electonics bench you might use a solder sucker to extract the solder remove those leads and solder from the other side of the board but I wouldnt bother wiht that it wont be any different from an electrical perspective.



take your new caps. wrap the lead around a pin to make it like a spring 5 turns or so..

slip the "spring over the lead stub that you left that went to the cap , crimp, a dab of solder too. mae sure you tin your tip and dont hold the heat there. if the tip is dirty you will have issues load the tip with solder and wipe it off with a wet sponge and repeat till the soldering tip is clean shiny and attracts the solder not black and dirty. the soldering only takes a second, you dont have to go holding the heat on there.

Id throw caution to the wind and use lead solder and not that new crap that has no lead. you aren't doing much here..


when i did the one from my van I did slip up and clipped the corner off a transistor and I chose then to order a new ECU from Rock auto.. so I didn't test it, I decided I'd better try to replace that transistor that I damaged before trying to use it.


i think those electrolytic caps can fail due to age, the other parts there are probably pretty well ok but electrolytic caps do fail often with age.

I keep some spares, I can start my 240 with the ECU from my 740 but since the 240 has the TDC sensor and the 740 has the distributor has a different ICU, the plug is different so you can't screw that up.

there is a handy chart floating around that explains ICU and ECU part numbers and there are differences Turbos are different.

years ago I sent a car to a mechanic with a no start issue and he swapped the ECU. I blew one once by accidentally getting jumper cables swapped around. I could hear it pop when I did that.

I think they are pretty robust but I wouldn't hesitate to swap the caps again I'd just be more careful not to clip a transistor.

I replace caps in old ( hollow state) radios as a side hobby , I see lots of those fail and with newer like 70's solid state electronics its very common just to do a full swap of caps in a shotgun approach.

there is a tool you can get to check them on the board without unsoldering , Its called an ESR meter.

most of the ones I deal with are in antique radios and rated about 400 V, some are 160V.. in the ECU it will be labeled the ones in my van were 16v , this is the maximum voltage the cap is rated for. keep the capacitance in microfarads the same as it is. if the voltage rating of the replacement is higher , like double, thats ok.

You want a pencil iron , a solder station will work , a soldering "gun" usually has a big tip and you want a finer point on the iron ..

keep away from he chips and be careful of static discharge , you can work on a wood table , not metal and ground yourself so you don't build up static like you may if you pet the cat or scrub your feet in the carpet. Static discharge can kill the programming flashed on to the chips and render it dead. best to keep in is one of those static bags that they, or some other board comes in.

you can wear a grounded anti static wrist strap, or simply make one a hunk of bare wire around your wrist and ground it will do fine for that one off job.

Consider getting a used one at a salvage yard.

I had one go on my '90 744 TI - the yard had hundreds of good used 700 ecus for NA cars but NONE for a turbo!

They write the cars mileage when they remove them and probably know how long they last.

If your 940 has a Regina fuel system with a Bendix ECU then you might have to wait a long time to experience a failure. Those ECUs are known for being robust, reliable units.

Thanks, everybody for the detailed responses. My car is a Bosch non turbo. When I have a chance I will have to pull out that panel to ascertain the parts number. Thanks, again!

Dear U.S. Diver,

Hope you're well and stay so. About 18 years ago (circa 2004) I bought spare engine and ignition computers (gently used), tested them (by replacing the factory-original unit and driving the car), and stored them in a climate-controlled area.

In 2004, these cars were a decade or less old. So, it could not have been clear how long the factory-original engine and ignition control modules would last. Fast forward: all of the factory-original units work well.

Still, should a fault trace back to the engine control (or ignition) module, I can take a "used, known-good" unit, install it (20 minutes), and keep on rolling.

My risk: that a "used, known-good" unit could "go bad", despite careful storage. I'll take that risk.

As used units are now >25 years old, it is best to buy a re-manufactured unit. Install it and drive the car for a few days. If all is well, put back the factory-original unit and keep the re-man unit for a "rainy day"!

Hope this helps.

Yours faithfully,

Spook

Thanks, all for your responses.

I guess this begs the question: from where would be the best place to source one? Used or Reman? The remanufactured ones run several hundred dollars. Would I have to remove my existing one in order to identify the correct replacement? Or would the model and year suffice?

Finally, is the replacement easy? Any pitfalls? Thanks!

It's of course a good idea to verify the part number of your existing ECU. If you haven't been there before, it's fairly easy to access. As Spook mentioned, it lives behind the right side panel in the passenger footwell. Start by removing the under dash panel, then lift the plastic sill trim (with a good yank straight up) and peel back the flex black edging starting at the bottom. A camera is ideal to take a pic of the label.

You don't mention if your '94 940 is an NA engine with Regina or a turbo with LH 2.4. If it's LH 2.4 then Bill Garland's ECU table is an excellent reference for part numbers http://www.nuceng.ca/bill/volvo/database/ecu.htm. The main thing with LH 2.4 ECUs is to match the EGR capability of your engine, which also determines whether a cold start injector is present, and as well matching turbo vs. non-turbo and whether there is Pulsair. The B230F NA (more properly a B230FD in later years) switched from Regina to LH 2.4 with Pulsair in 1995 (perhaps also the odd 1994 based on anectodal reporting I vaguely recall, possibly in different markets). EGR presence was normally market dependent, so if for instance you find a used LH 2.4 ECU in California or Canada, it's more likely EGR. Turbo 940s were always LH 2.4 without Pulsair, as was the early 940 B234F 16-valve.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Dear U.S. Diver,

Hope you're well and stay so. I cannot respond to your first question as to the best source for a re-manufactured ECU. As the factory-original units seem quite durable, I'd prefer to have two or three "used, known-good" units (factory-original), rather than a single re-manufactured unit.

Dave Stevens has wisely pointed out that a re-manufactured unit could have had only obvious failures remedied; other parts might be inobviously damaged. A 25-year-old factory-original unit could still have considerable life left in it.

Heat and humidity (moisture) are enemies of electronics. In sourcing used engine or ignition control modules, I'd look where lower - rather than higher - average ambient temperatures prevail. So, a unit from a car that lived in Nebraska or North Dakota would be preferred to a module from a car that lived in from Arizona or Florida.

On a 940, to ascertain the part number of the in-service engine control unit, you'll need to remove the plastic passenger-side foot-well panel (door-side). The ECU is held in a frame. You'll need to remove the ECU from the frame, but NOT disconnect it from the wiring harness. If I recall correctly, two or three T-20 screws need to be removed, to take the frame free.

For most normally-aspirated (non-turbo) 940s sold in North America, with the FD (non-turbo) engine, the Bosch Part number marked on the ECU is: 0 280 000 946. Some of the later '95 940s bear number 0 280 000 943.

I hope these comments are helpful.

Yours faithfully,

Spook

You're right, it is quite rare to hear about failed 940 ECUs here. The early LH 2.4 ECUs in the 240s/740s were known to occasionally fail, especially the 1989-1990 pink label ECUs. I expect a number of those ECUs that 940 people mention they've replaced are people throwing parts at a mystery problem without doing a full diagnosis and the ECUs were actually okay.

I wouldn't spend big bucks on a rebuilt one, certainly not as a preventative measure, but if you find a dirt cheap used one then perhaps grab it as a spare. It's always nice to have access to a spare used ECU as well as things like a used AMM, fuel pump relay and a CPS rpm sensor to swap in for testing to quickly help isolate a problem.

You have to realize that a rebuilt ECU is one that may have had significant problems and any repairs or testing they did may not have fully addressed looming issues like a whole bunch of aging capacitors slowly losing their capacity or a heavy load, electrical surge or static discharge that weakened a few components or damaged board traces. A warranty is only as good as long as the company is still in business and you don't mind waiting for a replacement to arrive (if they've even got one) and having to ship back after getting an RMA.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Understand your concern. Can’t speak to 940 ECU’s failing but certain 240 ECU’s are known to fail prematurely. Having a spare is a good plan.
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Will I buy another Volvo??? We'll see....