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This is a follow up to a message I posted over a year ago.
My Check-Engine light came on and the OBD Code was 2-1-2.
I then had a new Oxygen Sensor put in, but the Check-Engine came back periodically.
Now, after more than a year, it still comes back on.
But, strangely, during the winter when the temp was below freezing, the light
did not come back on. When it's above freezing, the Check-Engine light
comes on after driving for a few miles... It's really annoying.
Any ideas would really be appreciated!
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Believe it or not, I found the issue!
It's so ridiculous, that I'm almost embarrassed to admit it.
It appears that FUSE#4 WAS BURNT OUT.
I have no idea why I never noticed this before.
But, after replacing with a good fuse, the Check Engine light is off.
Thanks to everyone for all the good feedback.
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Good to know you fixed the problem!
However... a fuse doesn't burn out without an overcurrent event.
You had the O2S replaced, so the cause might have been abraded wires on the old one, as suggested by Art. In that case you're good.
If they weren't the cause, the actual problem might still be lurking there in the wiring loom.
A couple of years ago, a particular fuse would blow randomly in my 245, even when stationary and ignition off. It took me quite a while to find, and I found it more or less by accident when I moved the wiring loom in the driver's footwell around. A spark showed me exactly where the problem was. A wire had been chafing on the sharp edge of the black sheet metal designed to protect those wires.
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Once again I'm going to link to Volvo's service manual on the LH-Jetronic 2.4 fuel system TP31361/1.
It holds all the fault tracing procedures for this fuel system and may be helpful in finding the problem.
If I were presented with this fault, what I would do is warm up the engine and measure the voltage on pin 24 of the ECU connector while connected to the ECU. You can do this if you take off the connector's sleeve (which is the recommended procedure anyway) and reinsert it into the ECU conn.
A voltage of approx. 0.5 V is to be expected with the ignition on and a voltage that keeps swinging between approx. 0.1 and 0.9 V with the engine idling at normal operating temperature.
Alternatively, you could measure it at the firewall connector, but I prefer to do it at the ECU to include all the wiring between it and the O2S.
Good ground connections are important. On a 200-series, the ECU grounds on the inlet manifold, it has no ground rails closer by like on the 700-series, as I understand it from Dave's post.
If values were false, I'd first check if the heater part of the O2 sensor was getting 12 V through the yellow-red wire before condemning it. The heater part can be checked for by resistance measurement. 3 Ohms at 68F, 13 Ohms at 660F (idle), see section E23 of the manual.
The biggest challenge here is the intermittent nature. That type of fault may take a lot of time to track down. Carry a meter and some tools with you. I sometimes hook up a meter permanently to see what the values do while driving. The min/max-hold function (if equipped) on the meter can be useful to keep your focus on the traffic instead of on the meter.
Also very useful is this website.
Is 2-1-2 the only stored code, or are there any more if you repeat the read out directly after getting the first code? What about codes on the other socket (#6)?
Good luck! Please report back what you find.
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"If values were false, I'd first check if the heater part of the O2 sensor was getting 12 V through the yellow-red wire before condemning it."
Over the years this has been the trouble for occasional 212 codes. The usual problem is fuse #4, either blown or just crusty on the ends, so my approach would be to simply check for battery on the fuse terminal on the right side of #4. This fuse protects the wiring to the oxygen sensor and to the tank's fuel pump. Neither the sensor's heater nor the tank pump is necessary for the car to be driveable.
Easy check and I'd put it in the first category. If the fuse is blown, the usual short is abraded wires at the oxygen sensor itself.
Second check would be the resistance measurement you suggest. To thoroughly check, warm the car for a few minutes. With ohmmeter at the ready, quickly disconnect the heater plug (the two white wires) and read the resistance toward the oxygen sensor.
A good one will start out at somewhere near 13 ohms and as it cools, slowly decrease to about 3-4 ohms. Watching it go through the heat cycle without interruption assures you the heating element isn't broken internally, which can be causing an intermittent connection.
--
Art Benstein near Baltimore
Why do banks leave vault doors open and then chain the pens to the counters.
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"Over the years this has been the trouble for occasional 212 codes. The usual problem is fuse #4, either blown or just crusty on the ends, so my approach would be to simply check for battery on the fuse terminal on the right side of #4. This fuse protects the wiring to the oxygen sensor and to the tank's fuel pump. Neither the sensor's heater nor the tank pump is necessary for the car to be driveable."
Agreed. I tend to try to include as much of a circuit as possible, but with a "usual suspect" (the fuse), it's perhaps quicker to focus on that first.
Looks like you have some sort of heat shield there in that photo. It's something mine doesn't have (nor did my previous 92 245).
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I still don't get it.
Why would an electrical connection issue work differently
depending on the outside temp?
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Electrical connections that age are often made higher in resistance or can even go open circuit caused by only an incredibly thin layer of oxide. That's why disconnecting and reseating a plug or connector is often enough to restore the contact, at least temporarily.
Gold plating is often used to mitigate this oxidation process.
Cold and heat make materials contract and expand, different materials at different rates. Your connector might grip the counterpart harder in the cold if the latter has contracted less.
Suffice to say that really tight connections won't suffer from this, but ones that have lost tension over the years are more susceptible.
At least this seems logical to me, but for all I know I'm talking out my...
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I will try to check some of the connections as well as Fuse#4.
The O2 Sensor heater wires are intriguing...It could explain why the Check Engine light stays off during cold weather.
Today I drove the car at least 15 miles in 40 deg. weather, and the light never came on.
This issue usually happens when the outdoor temp is closer to 50 deg.
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2-1-2 on OBD port 2 is signal missing/faulty from oxygen sensor . You've replaced the sensor once in an attempt to deal with it being a faulty signal, so perhaps think a little harder on the missing part.
I checked out the discussion in your O2 sensor problems thread from a year ago. Based on all that you've done so far and what you're now saying, the problem smells to me like an intermittent missing signal, possibly even seasonal in nature. I'm very much guessing you've got a poor electrical contact somewhere in the O2 sensor wiring circuits.
Art mentioned carefully inspecting fuse 4 which is for the O2 sensor heater circuit and fuel pump. That fuel pump circuit is one of the more notorious problem areas as it is high current draw, especially with aging fuel pumps.
I'll further suggest checking every connection in the O2 wiring starting at the firewall connector and working your way back to the ECU. Peel back the rubber connector boots to make sure the pins are solidly pushed in from both sides -also pins at the large main connector blocks.
Anytime I see mention of intermittent seasonal behaviour with 240s, I immediately think of possible chassis ground problems. With that in mind, I'd be very, very suspicious of the black wire having a solid chassis ground connection. You can start by checking with a meter, but I'd want to do a proper inspection. I don't recall where the O2 sensor black wire attaches in the LH 2.4 240s, but for a 740 it goes to the ground rails behind the ECU. Make sure all chassis ground connections in such areas are clean and solid - wiggle and remake connections as needed.
Is there any chance someone has ever had the ECU connector off for diagnostic testing or replacement? I'd want to pull the connector for inspection and reseat it, including removing the connector shell to make sure no wiring is damaged. The O2 sensor (pin 24) is one circuit that technicians sometimes want to measure there. If people aren't careful with probes, the little contact fingers can get bent and make for a poor connection. Dirt, like dust and hair getting caught in an opened connector can also be a problem. BTW, as much as the original '89 LH 2.4 ECUs are well known as troublesome, I've not of heard of the onboard O2 sensor circuit being a problem.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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"Anytime I see mention of intermittent seasonal behaviour with 240s, I immediately think of possible chassis ground problems. With that in mind, I'd be very, very suspicious of the black wire having a solid chassis ground connection. You can start by checking with a meter, but I'd want to do a proper inspection. I don't recall where the O2 sensor black wire attaches in the LH 2.4 240s, but for a 740 it goes to the ground rails behind the ECU. Make sure all chassis ground connections in such areas are clean and solid - wiggle and remake connections as needed. "
On the 240, a three-wire sensor is used. Its black wire is the sensor output, not a ground. The heater is isolated to the two white wires. The black one connects to the shielded green wire to the ECU below the windshield wiper motor.
In your 7/9 cars have you replaced the original with a four-wire sensor? I think this is a good idea, because it bypasses all the rusty exhaust plumbing originally designated the ground return for the oxygen sensor when these cars were built.
I grounded my four-wire sensor to the same bolt where the radio noise suppression ground strap for the cam cover grounds at the firewall.
--
Art Benstein near Baltimore
Why do we leave cars worth thousands in our driveways and put our useless junk in the garage.
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Hi, Art. Yes, I was hastily referring to a 240 schematic without wire colors and managed to forget that the heater circuit is two white wires with a shielded black signal wire rather than a single white wire and two blacks -at least I did correctly note that in a recent discussion we had here on O2 sensors. That's right up there with remembering that the black wire on most of the 240 in-tank pre-pumps is hot, not ground -made that mistake only once on a car running the pump backwards, won't likely ever forget that now.
I have not felt the need to go to a 4-wire O2 sensor, but I certainly wouldn't hesitate to use one. Between rusty exhaust connections and people using anti-seize, I've always thought a separate ground was a much better idea.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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Hi,
Does your engine use an EGR valve?
If it’s not getting turned on in a timely manner it will trip an engine light.
There’s a electric valve that controls vacuum to the EGR valve and it gets plugged up from being able to vent. When this happens the EGR temperature sensor doesn’t send a “change in signal” response to the ECU and that trips on the check engine light.
There is a piece of foam rubber under the vent area cap on top that rots.
A change in the material from moisture or temperature affects the venting.
I replace mine with a piece of polyester fuzz or pillow stuffing. Polyester doesn’t rot.
It can still get dirty and I have only change mine once again more in the 17 years. I have own that 1991 car. It now with 100,000 more miles! 284K and still counting!
It was sold to me because the young lady kept chasing the light and her Indy kept guessing at her expense. She wanted a Mazda Van for her expanding family.
I found the problem after it wouldn’t smog because of the light came on while going to get the certificate!
When bought the car, it didn’t have a light on because “they,” an associate helping her show the car, kept pulling the battery wire off from the little box on the left fender, just before it was test driven each time!
Since this was my first 240 with a CEL, I didn’t really understand the codes so I cannot sat what it was.
Since then I have come to realize that those codes are so generic it almost laughable!
I call it a shotgun blast to a side of a barn!
Yes, you will hit the barn, but in so many places, you’ll learn how sneak up on the most dense spots!
Don’t get to caught up into the code number!
Phil
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