I recently bought a 95 s90 and I absolutely love it, but I'm having issues with the cel I knew about it when I purchased the car and reading them has got me stumped, I put the connector in socket 2 on port A and I get codes 112 and 212 I'm sure 212 is the oxygen sensor but I've read 112 could be ecu failure or fault in the fi control unit, how do I go about fixing this? I'm stumped on if it's the ecu or the fi unit, it's a 2.9 liter if that helps, thanks in advance

 

For motronic 1.8

 

So should I go ahead and replace the knock sensor? Or is there a way to ohm it out? I'm trying to get it ready for emissions any idea how long after I clear the code the system will be ready to test?

 

You might fail because the check engine light is on, but the OBD1 has no monitors to go ready, the emissions test station does not have the capability to communicate with it.

As far as I know the only way to verify that the knock sensors are working is to use an oscilloscope. Due to their design I can't see how one can fail, but a wire might be broken.

 

So could the ecu in fact be faulty? They won't test it with the light on I could clear it and go but I'm trying to fix the problem not hide it Ya know? I followed the wires by the starter and didn't find any cut or burnt

 

After you reset the faults, how long does the check engine light stay out?

A "fault in memory circuits ROM/EPROM or RAM" should appear instantly - the ECU checks these as soon as battery voltage is applied. If it takes some time to appear, I would bet money that the memory circuits are not bad. This does not eliminate the bits in the ECU that interface with the KS or O2S though. They are pretty rugged electrically, though.

I think there is nothing wrong with clearing the faults and taking it for smog, because if it passes the tailpipe sniff on the dyno it's a legitimate pass. You could then register the car and fix it at your leisure. If the light comes on every time you drive, though, it's a good chance that it will come on during the smog test, that would make it a waste of money to try.

You can get a wiring diagram from here Volvo Wiring Diagrams
The wiring diagram is confusing but it will make more sense after you look at the whole document. I know it's a lot to take in, but these are the best references for the electrical parts of the car.

You should be able to probe the KS and O2S from the "A3" connector complex. I would use an oscilloscope for all three (there are two KS) but sometimes a voltmeter can give insight into the O2S.

The oxygen sensor fault should be easy to remedy, simply an O2S that has over 100,000 miles on it should be replaced. At rockauto the cheapest Bosch o2 sensor is actually the Bosch brand - the $20 ones are not the same. You should be able to tell if yours is very old by its physical appearance. There is a date code on the sensor but it's usually impossible to see while it's installed. However there's that other fault about the ECU or KS failure and an $80 O2S might end up being a waste of money if you never get that one resolved.

 

Hey, I just learned that your car was made right around the changeover between two types of EFI (Motronic 1.8 and 4.4)

Can you get under the car to look at the oxygen sensor, and tell me if it has 3 or 4 wires?

If you have Motronic 4.4 the code meanings are different from what I pasted above.

 

I work until ten but when I get home I will is the 3 wire 1.8 and 4 wire 4.4?

 

Knock sensors don't seem expensive but there's two? Were are they located? I know one is located by the starter

 

Yes, 3 wire O2S = M1.8, 4 wire = M4.x

You can see this drawing for the approximate locations of the KS:
https://i.imgur.com/WnkoraZ.png

They are on the intake side of the head, underneath the manifold. To R&R the front one they have you remove the MAF and intake hose. For the rear one they want you to remove the starter and oil dipstick tube. Not fun!

You might be able to get your eyes on them from under the car.

The KS have two terminals each. One terminal is ground, the other is signal. On the wiring diagram all the grounds are tied together and go into the ECU pin #30. (I'm looking at the schematic in TP3909202)

The A3 connector complex is readily accessable under the hood, in one of the fuseboxes. The box is sealed, so when you get the cover off you should see that you can easily probe these connectors by going in next to the individual wires.

If you have M4.4 (4 wire O2S) the 112 code does not show the KS as being one of the failures. I have conflicting information about which Motronic is installed in the '95. The wiring diagram shows a configuration like M4.4, but the service info I have shows M1.8.

You can see the difference in the two O2S by looking at photos of the Bosch sensors for the 1994 960 and 1995 960. If you have a four wire sensor you should find the connector near the automatic transmission dipstick.

If it turns out that you have the 4 wire sensor, here is what can cause 112: (Motronic 4.4)

 

That makes sense my temp gauge goes crazy, it'll bounce all over the place I figured it was the thermostat, I'm in the process of doing water pump and thermostat so I'm probably doing the temp sensor too I hope it's the 4 wire one!

 

Here's my vin YV1KS9615S1057213 the 8th digit is for emissions? But I can't find anything related to number 1

 

The temp gauge and ECU use different temperature sensors. Your gauge on the dash may be flaky because of broken solder joints in the cluster - I have the Yazaki cluster and it did the same thing, and the solder joints break because they used a polymer flex instead of a real PC board in the cluster. That's real easy to repair.

The emissions are specified on the data plate on the radiator support, but I haven't seen a table of what the values mean.

Back to the CEL, how long does it take to come back on after you clear the fault codes? Have you correlated anything with the lamp turning on, such as driving uphill or the engine warming up? I think this is an important clue.

 

I haven't cleared them I bought the car with them on, I'm replacing timing belt and water pump tomorrow then I'll clear them and see about how long it takes for it to clear

 

The gas gauge is jumpy as well but not as erratic as the temp, is there a thread on this repair?

 

Our fuel gauge was screwy when our battery went bad. I noticed that it was charging at 13 volts (idle), replaced the battery and it went up to 14 volts which is reasonable. At that time the fuel gauge started acting normally.

I may have written something about the cluster in the "my new S90" thread in the S90 forum here. There's not really a whole lot to say - my biggest complaint was the lamps that light up the fuel gauge and temperature gauges were working intermittently, and I could make them come on again by reaching under the dash and touching the back of the cluster. At this point I knew what was wrong, so when it was convenient to remove the cluster, I did and took it into my shop to repair the solder joints. All that's needed to fix broken solder joints is to heat a joint up until it melts, and add a tiny bit of solder. If you do this, do it quickly because the flex circuit is plastic and can melt too. I normally keep my soldering tool set to 375 degs C and it literally takes two seconds.

Good luck doing the timing belt and water pump: when I did this the tensioner needed replacement, and so did both of the rollers. Member rspi here made a fantastic set of videos about this and published them on YouTube. I bought a Gates timing kit and it came with factory original rollers and a "made in UK" belt, and I don't like that idea so much so I will replace it with a Continental belt when I replace the water pump. I don't dislike Gates, but I have no idea who made that UK belt and know that Continental is the best of the best. Then, I found out that the dealer price on the timing kit (belt and 2 rollers) was really good, and should have looked there first.

 

I don't have issues with my lights the gas gauge just seems to be off or float a little bit but the temp gauge bounced all over the place I found a receipt from Volvo that the last owner brought it in for erratic temp gauge and there was a quote to replace the thermostat, but my water pump leaks so I'm thinking it may be due to inconsistent coolant flow,or the temp sensor under the thermostat I purchased the gates kit for 185 off Amazon with everything included I figure if I'm going Into it that far I might as well do it all, I'm going to check and tell you the wires on the o2 so I can figure my check engine lights out

 

4 wires on that o2 sensor two white a black and a grey

 

I owe you an apology, I had a misunderstanding, I think your car has M1.8 and Volvo changed over to the new style O2S for one year before they used M4.4. Sorry for my error.

Please look at the PDF Wiring Diagram for the '95 960 from the link in my earlier post, page 96, can you remove the cover from the A3 connector so that you can probe with a voltmeter?

The cover can also be removed from the ECU connector, but this is more difficult to get to, it will be easier to probe from here.

 

The diagram only goes to page 44, can you tell me what Color wires and what resistance I'm looking for?