Hey all! Avid reader here, first time posting.. Been researching a lot into the issue, and I think I have it figured, just wanna verify.

Got the 1-2-3 and 2-2-4 Errors on 1992 Volvo 240, 2.4LH, indicating an issue with the coolant temp sensor. The background to this is as follows. Was having fuel system issues throwing 1-1-3 code, and was throwing one for crank position sensor as well.. Had some spare money, so decided just to go all out. Changed spark plugs, wires, thermostat, all 4 fuel injectors, fuel pumps, and fuel filter. Cleaned throttle body, changed TB and intake manifold gasket, replaced flame trap and PCV elbow hose, as well as some fuel line hose at the fuel rail, changed crank and coolant temp sensors also.

As far as testing, I tested (and cleaned) the IAC Valve, tested the MAF, Throttle switch, etc. It was at a no-start before all of this was done. It fixed the 1-1-3 and the no-start, though the idle was still rough. Drive it around a little, and it throws the 1-2-3. Check my connections and the resistance across the temp sensor. I also checked the voltage coming through the wiring harness upon cranking. All looked good. I drive it around some more, stop it at a friend's house, and boom... Won't start. Upon reading some stuff on here, I took the harness out of the ECU, behind the plastic on the passenger foot well. Now, I'm half ashamed to ask, but I'd read that if you run a multimeter between pins 13 (temp sensor) and 5 (ground), then turn the key to on, you should be getting voltage. My question is, is this measuring it on the actual prongs coming out of the ECU, or the corresponding slots on the wiring harness which plugs into the ECU? I ask because I read that if no voltage is read at those pins, it's indicative of a bad ECU. Just need to know where to go from here. Thanks ahead of time for any help you can offer!

 

well, if the ECU is unplugged, there won't be anything at the ECU's own pins. any voltage readings have to be done with the ECU plugged in, whcih means you've opened up the back of the connector and are probing the pins, be careful, real easy to short stuff etc.

typically for CTS (coolant temp sensor) measurements, I've used an ohm meter on the pins in the ECU harness plug when its unplugged.

 

Awesome, appreciate the response! As far as I can remember, the ECU itself is still plugged in. I pulled off the piece closest to the passenger door.. Opaque plastic piece with all the wires running into it. Going back to work on it tomorrow, will likely take pics just to ensure I'm testing the correct areas. I'd hate to splurge for another ECU if it's just a wiring fault, but I'd also hate to cut open the bundle of wires and go through all the trouble if it's a bad ECU.

 

Here are the pics I promised... The opaque plastic is all that's unplugged from ECU. Do I test the back of it, or the ECU itself? I'm assuming the ECU, as the other piece doesn't really actually have "pins" coming out of the back. They're more like recepticles.

 

the plug in your 2nd pic, you have to take the yellow shell off it so you can probe the wires on the back of it while it is plugged into the ECU, that way you can take measurements of the live system.

 

Fantastic! Based on what I see around here, you seem to be the man, Pierce. Much appreciated!

 

So, I checked it while the engine was cold (as it won't start). Temps in the area have been about 80-90F lately. It's giving a voltage reading of 4.72, which seems super high to me, based off what I've read. That coupled with the complete lack of resistance leads me to believe it's a wiring issue. Thanks for the help again.