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  #1  
Old 05-07-2011, 08:59 PM
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1991 Volvo 740
 
Join Date: Jul 2010
Posts: 30
Default 740 Error Messages, Head lights, Battery question

Hi guys,

my 1991 740 wagon is acting up, and because all those things happened at the same time, I wonder if there's a connection:

a) 4 days ago I got the 'Check Engine light'. I read the codes:
1. 'Battery Voltage to low/high' 1-3-2
2. 'Fuel trim (lambda control) too lean at part load' 2-2-1

b) 2 days ago, suddenly my headlights don't come on - when I turn the switch to medium pos, the 'small lights' come on, and the dash lights, but on 'full', the lights are all off (head, tail, dash).

I measured the battery with everything off - 12.3 volts. Very low - but I never have problems starting the engine. Odd? If the battery was dead, I would expect starting trouble.
I pulled the head light switch - no visible trouble. I had read in another thread that some people had a broken switch. I ohm-metered the switch in the three settings, and found that some contacts open and close, but I don't know which ones should open and close, so not sure. There doesn't appear to be one central fuse for the switch, but separate ones (behind the ashtray). Looked them over, none seems bad.
I looked at the hose assembly at the air flow sensor, trying to locate leaks. Nothing... Fuel economy doesn't seem worse than usual. (25 MPG, mostly highway).
I reset the codes once, drove some 20 miles before the check engine light came on again. No battery warning this time, but again the 2-2-1 code for the lambda control.

I'm confused. Is the battery, the lambda, the light switch trouble all a coincidence?
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  #2  
Old 05-07-2011, 10:31 PM
pierce's Avatar
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1992 Volvo 745
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i wonder if you don't have a bad ground or something, that throws everything off, includinig the charging

when the car is running, take a DVM and measure the voltage between the battery - terminal and the engine, also the frame of the car (at a ground screw or whatever). the voltage difference should be really small.
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  #3  
Old 05-08-2011, 02:31 AM
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O.K, straight off, forget anything being wrong with the o2 sensor. People see the code and "lambda control" and instantly run around changing o2 sensors. All it is reporting is that the o2 sensor detected a too lean/rich condition. Just about ANY fault in the fuel and ignition management will light an o2 code.
I think Pierce is heading in the right direction, I would firstly check all wiring coming from the alternator. I don't think it's a bad ECU earth, it would show up as all sorts of weird stuff. Another possibility is failing alternator brushes, I've seen intermittent voltage spikes on other vehicles when they were wearing low and momentarily losing contact now and then.
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  #4  
Old 05-09-2011, 11:25 PM
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1991 Volvo 740
 
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Thanks Pierce and Typhoon. I haven't had a chance to follow your advice yet, will do so tomorrow. The 'Check Engine' light is often off for the first few miles and lights only afterwards.
As for the main lights not working - is there a possibility that it's the ignition switch? I say this because the switch had been kind of sticky at times, not fully engaging. This once led to me going on the highway for some miles at 55mph but at 4000 rpm as the car wouldn't shift higher. Also the radio didn't work (which wasn't really my biggest problem at the time :-)
Or is there some central relay for the lights that controls multiple bulbs (including the dash)? I got the '1989 Volvo 740 Electrical Wiring Diagram', but can't make much sense of it, I don't even find the headlight switch in there at all...
Thanks again for your help!
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  #5  
Old 05-09-2011, 11:53 PM
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1992 Volvo 745
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the volvo wiring diagrams take some getting used to. I'm assuming you have a greenbook?

on my 92, there's a couple relays behind the fuses that control the headlights... here's the schematic page from a 95 940, the headlight switch is 3/2. 3/5 is the lowbeam switch (truth table under it shows its connections). 3/1 is the ignition switch. 2/37 and
2/50 are the headlight relays. 7/75 is the bulb malfunction module.
http://www.hogranch.com/files/volvo/...headlights.pdf

there's an index at the end of the book
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  #6  
Old 05-10-2011, 12:57 AM
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1991 Volvo 740
 
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That's great Pierce. I don't have a 'Green Book', but your comment made me search around a bit and I found this:

Electrical: Circuits, Relays

So my next step will be to look at those relays. Incidentally, I didn't try if switching to high beams makes the lights come on. Apparently, sometimes those work...
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  #7  
Old 05-10-2011, 01:09 AM
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to get to my relays, I had to put the shifter in 1st (parking brake set), then remove the sh tray to access the fuses, take the cigar lighter out, unsnap the bezel immediately around the cigar lighter, and there's two phillips screws, remove them and the storage tray comes out. NOW I can access my relays...
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  #8  
Old 05-10-2011, 08:02 AM
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Have you tried to jiggle the ignition key after you start the car. You may have a bad contact in the electrical part of the switch. If the headlights are out after the car is running just move the key a little and see if they come on. Our switch went after 300,000 miles. Start the car OK and had no windows or heater fans or lights or radio.
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  #9  
Old 05-10-2011, 09:42 PM
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1991 Volvo 740
 
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I jiggled the key but no dice.
I now hold that big fat red round 'lamp failure relay', I read that this sometimes goes bad and that this would cause exactly what I see - low beams off, but while I pull the high beam lever, high beams come on for as long as I hold the lever. I'll have to figure out how to pull the cover off the thing and check the solder joints.

http://cgi.ebay.com/ebaymotors/ws/eB...m=260780502789
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  #10  
Old 05-10-2011, 10:50 PM
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the lockup function of the highbeams isn't in the big red round lamp failure thing, its more likely the headlight relay, which is, I believe, "K", the 2nd relay from the driver side on the lower row of the relay panel behind the ashtray on a 740/940.... the red can is strictly the bulb failure sensor, its not in the path of the lamp power, rather its on its own set of wires that run from the lamps back to the failure module and are used to sense current flow. you could, I believe, REMOVE the failure module entirely, and everything would work without it.
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Old 05-10-2011, 10:50 PM
 
 
 
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1989, 740, 91, battery, beam, dashboard, died, head, headlightsparking, lights, low, main, relay, stock, switch, unit, volvo


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