I just bought my first Volvo, a '94 850 Turbo wagon. I bought it at a signifigantly discounted price with the knowledge that it had some kind of electrical problem. The mechanic who worked on the car last said that he had gotten it to run by manually closing the (faulty) injector relay. Well I've replaced this relay and now am getting no spark. I have replaced the camshaft position sensor and coil as well as the power stage. When I try to check for codes on diagnostic unit bank A, terminal 2, I get nothing. Only a weak and constant glow from the LED without pressing the button. When I push the button the LED illuminates fully, but no codes are sent after. I get the same thing from the socket inside the car. I can however collect codes from some of the other terminals on the self-diagnostic unit under the hood. I have switched ECU's from another 850 with the exact same result. This would lead me to believe that its a case of a bad connection along the yellow/brown wire that connects the two diagnostic ports to terminal B5 of the ECU, except when I pull the ECU, the led no longer glows dimly. I believe that whatever is wrong is preventing me from getting any spark or other functioning. This problem is driving me insane and I figured I should ask if anyone else has ever seen anything like this before I start removing and checking miles of wiring and maybe find nothing anyway. Any insight would be tremendously appreciated. Thanks

 

I've found the thing to be a pain in the *** too...
I've pulled codes, but it doesn't act completely correct...

However, try to clean the terminals first and see if that might work...

 

Greetings.

Sorry about the problem.

If you've checked each spark plug wire and none is firing, the problem may be upstream of the ignition coil. If everything appears ok after visual inspection (cap & rotor), refer to the attachment; I've circled possible components that may have problems. Go over each component that was replaced, and double check for positive connections, especially grounds. If everything seems ok, it could be the ignition switch, overload relay, or the CEU (Central Electrical Unit [the fuse box in the engine bay], not the ECU) may have wiring problem. The problem could also be anywhere I did not mention, though.

When you remove the ECU, disconnect the negative battery cable and wait at least for 15 minutes, or the ECU may suffer permanent damage. However, when you do this, write down the code for the radio and make the ECU re-learn idle after reconnecting the battery.

Also, check for good engine-to-body ground.

I hope this is of some use.


JPN

 

Thanks for the info. Particularly the diagram of the sensor grounds. There is so much wiring packed into the engine bay that it is a nightmare even with wiring diagrams. I'm suspicious of the CEU because the previous owner lost the cover. I tried to remove the fuse panel and look underneath, but it didn't want to come out because the wires underneath weren't long enough. I could kind of see a little ways underneath and it looked OK, but there is a low point closer to the windshield, like where the relays go, that I still couldn't inspect. Do you happen to know what the different sockets on the self diagnostic unit correspond to?. I'm guessing that the A side is probably for the EFI computer and the B side for something else but what about the individual numbered sockets? All of the sockets on B work and give codes, but the sockets on don't except for one or two of them. My understanding is that A2 is where engine codes are (ie. sensor faults etc.) collected. Thanks very much for your help.

 

Hello again,

Some sockets are not used, means they are empty; no wire is attached so you will not get any response.

Some examples:
A-1: Transmission (Aisin-Warner AW30-43 & AW50-42)
A-2: EFI (Fuel Injection Control-LH2.4/3.2, Motronic 1.8/4.3, Fenix 5.2, Regina: Yours is probably Motronic 4.3, if it's '94 Turbo B5234T engine)
A-3: ABS
A-4: Don't know
A-5: Don't know
A-6: Ignition Module (you need to check this)

B1: Don't know
B2: Cruise Control
B3: Don't know
B4: Don't know
B5: Don't know
B6: Don't know

There are also sockets for Climate Control, Instrument Panel, Power Seat diagnosis, etc... I don't have my Haynes manual with me right now, but others may be able to tell you what those "Don't know" sockets are for.


JPN

 

The last half of the manual.

As to the CEU wire connections, I assume the wires are ok, but if it's been missing the top cover, some water & dirt might have entered and preventing good connections between the relays/fuses and the female sockets. I would use electrical contact cleaner into the female sockets, with the ignition switch off (ideally with the battery disconnected) and definitely get the cover, possibly from a junk yard but check with a dealer to see how much they want.

To see if a socket on the OBD-I terminal is empty, you canlift the terminal off & see the back of it (it's simply inserted into the holder on the ECU box).

Good luck,


JPN

 

From Bay13 from Volvo Speed.

A1 Transmission
B1 Climate Control
A2 Fuel System
B2 Cruise Control
A3 ABS
B5 SRS
A5 TCU (Transmission Control)
B6 Power Seat
A6 Ignition System
A7 Combined Instrument

 

Thanks again for the responses. The struggle continues. I'm going to try to isolate the ignition module as a first step and then see if I find anything new. If you get a chance JPN, could you repost the diagram of the camshaft and engine speed sensor grounds? I don't know where they went, but maybe this site truncates older posts to minimize space by removing .jpgs etc. Thanks again.

 

Hello,

Sorry for deleting the pics. I deleted them (not the problem on the forum), as they are courtesy of Volvo. I thought you've saved them in your PC so I deleted them, but here it is.


JPN

Attachment deleted.

 

Attachment deleted.

 

Here's the last post.

Someone else has had a similar problem; in his case he keeps getting the same codes (misfire in at least one cylinder), after having done an ideal tune-up. For him, all I could think of without actually testing the car myself, was to check the ignition wire & spark plugs. On rare occasions, new parts are defective.

Let me know how it goes.


JPN

 

Well I'm still stumped. However, when pulling components and experimenting, I noticed that with the transmission control ecu removed as well as the abs control unplugged, I got the number 2 test socket to work for a minute. I also noticed that the big idle control solenoid started to hum while the #2 socket was (briefly) working. I havent' been able to replicate this though, so I don't know what made the difference. My next step is to either purchase a breakout box for the Motronic ecu, or rig up test leads to the pins myself. Thanks for the feedback. I going to just keep on trying but I figured I'd post an update to the situation. Thanks.

 

Hi,

>My next step is to either purchase a breakout box for the Motronic ecu, or rig up test leads to the pins myself.

I think the latter would be better, as the terminal (breakout box?) will probably be a few hundred $$$ at the dealer. I'll attach a home-made tester diagram. I feel there is a loose wire/connection to the OBD-I terminal.


JPN

[IMG]local://upfiles/6892/F87BB9DB57E44B4D8CC86EDBE7E3D65C.jpg[/IMG]

 

Thanks for the diagram. I rigged up something very similar out of a resistor , 3 pos. switch, LED and some wire and an old pill bottle. However, testing at the in cab socket, I get the exact same dim glow immediately upon hooking up the tester. I am a technician at an electronics manufacturing facility and was discussing this with an engineer the other day and he made an interesting point. The dim LED made me think low voltage, either a weird short (water) or a bad crusty ground. However he pointed out that perhaps the dim LED is really a very fast pulse off and on. To my eye this could look like a dim light. I never thought of that . I'm going to root around in my garage for an oscilloscope and see if I can see a pattern. I'll post any results. Thanks.

 

Hi,

Yes, the red LED does look dim when it flashes. However, it should only flash when codes are cleared. I'm suspecting the terminal (breakout box) itself for poor wiring, or there may be poor connection (s) in one of the ECU'spins. You could disconnect the battery, wait 15 minutes (for the power relay to stop supplying voltage to the ECUs) and remove the 2 (3) ECU boxes and clean the connections with electrical contact cleaner & air duster. Well, since you're an electronic technician (like Mr. J Telectro), you know better than I do.

Will wait for your update.


JPN