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240 Occasional 2-3-1 code LH 2.4

D

dandeluca

Member
Joined
Jun 17, 2020
Location
Bordentown NJ
Ever since I?ve had my 91 240 it will throw an occasional 2-3-1 code. If I clear it it might stay off for a month or two or it might stay off for a week or two. (I don?t drive the car daily but I use it a few times a week.) The car seems to be running perfectly. I have replaced the oxygen sensor already. Any other idea what might cause this occasional code? I was thinking of replacing the accordion tube after the MAF but it looks pretty good. It more an annoyance then anything else but I sure would like to keep that check engine light off.
 
Oxygen sensor code:


Get A TEST LAMP and connect it between the two white wires. Illuminate? This checks the heater circuit.
 
What 02 sensor did you buy? I bought an NTK one in the past and after a few months of use the LH2.4 didn't like it and threw codes. Went back to a Bosch universal sensor and it has been fine. Also check your ECU number to make sure you don't have a pink label 561 ECU.
 
The fuel ecu is in the right side kick panel. The Bosch label can be pink and the bosch part number will end with 561. If you have that ecu plan on upgrading to a 951 version. They are cheap on the board or ebay. If the label is white you are probably ok and it may be a flaky connection in the wiring.
 
Check your fuses (#4, iirc) for corrosion as well. My 92 240 recently threw that same code with a fairly new O2 sensor.

Found fuse 4 was looking pretty corroded and crusty. Cleaned contacts, new fuse and it went away.
 
ZVOLV said:
Get A TEST LAMP and connect it between the two white wires. Illuminate? This checks the heater circuit.
Click to expand...


This would take 30 second with a test lamp......

Heater circuit verified? THen check your signal wire with a meter. Whats the voltage reading when the car is warmed up? Pegged at 0.1v or 0.9v is no good. Also faster and easier than posting a reply on tbricks.

GET OUT THE TOOLS
 
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I did have to start the car to get voltage, but the heater circuit has power. Next time it throws a code I?ll try looking at the signal voltage. I cleaned up the fuse box, nothing looked too bad, but I cleaned spots 5 and 6 and thew some fresh fuses on their for good measure. Maybe this winter I?ll upgrade to a modern spade fuse panel.
 
dl242gt said:
Yes, just turn on the key and the heater circuit should power up. The signal will have to be checked with a meter and warmed up engine.
Click to expand...

:smile: This is probably one of the few things that does need the engine running. Fuse 4 is powered by the fuel pump relay and its only loads are the oxygen sensor heater and the lift pump in the tank.

The method I use to check the heater is more than just knowing voltage gets to the plug on the firewall with the two white wires from the sensor harness. I want to know if the heater itself is working.

My method is to run the engine for a few minutes to warm up the sensor, then shut off the motor and quickly pull apart the two-pin plug with the white heater wires in it. Quickly connect an ohmmeter looking toward the sensor's heater. A good heater will read somewhere near 13 ohms and as it cools fall to about 4 ohms plus or minus a few. The idea is to see it cool without any interruption in its resistance decline that would mean the heater element opens with a change in temperature.
 
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dandeluca said:
Ever since I?ve had my 91 240 it will throw an occasional 2-3-1 code. If I clear it it might stay off for a month or two or it might stay off for a week or two. (I don?t drive the car daily but I use it a few times a week.) The car seems to be running perfectly. I have replaced the oxygen sensor already. Any other idea what might cause this occasional code? I was thinking of replacing the accordion tube after the MAF but it looks pretty good. It more an annoyance then anything else but I sure would like to keep that check engine light off.
Click to expand...

I've fixed this in the past by cleaning up exhaust leaks. In particular, exhaust manifold gaskets and the one between the header pipe and the manifold. Before being surprised by that I've tended to ignore the 231 that shows up every now and then.
 
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