Dr. Porter,

As Uncle Art says. I forgot the 02 sensor heater function receives power at all times while the fuel pumps run.

For some reason, I thought the fuel control computer had a driver for the 02 sensor heater, disconnecting when the 02 sensor heater when reached a high enough resistance (temperature) across the 02 sensor heater element (and when the heater and / or exhaust gases provided adequate heat). (Sorry for my confusion, I used to futz with other makes and models of auto recently, usually helping a neighbor. Too capricious, on my part.)

So, the 02 sensor may not reach function fast enough as the fuel control computer is programmed to expect. Thus, your fault code and check engine light is on.

When you run the engine on your 1992 Volvo 240, voltage to the 02 sensor remains ON. The load reduces as it heats up and thus needs less power.

As your Volvo 240 does run and drive, and #4 fuse in 1992 Volvo 240 power / protects the in-tank fuel pump and the 02 sensor heater. The fuel injection relay and the fuel pump connect to the feed (left side) of the #4 fuse. The load (right side of the #4 fuse on the fuse box) is the in-tank fuel pump and the 02 sensor heater, unless the linkedin 1992 240 wiring diagram is wrong. Power to the fuel system relay comes through fuse #6 (though not a worry, now.)

So, like Art B. says here, check the heater. Unlike the 02 sensor, the heater does not have a negative volts DC ground through the exhaust manifold piping.

See the 1992 240 wiring diagram in the PDF file.
http://www.volvowiringdiagrams.com/?dir=volvo/240%20Wiring%20Diagrams

So, as you have played swap-a-sensor, what we would like to avoid, you may want to use your trusty multimeter to verify fault.

Here is an image diagram of the Volvo 240 Oxygen (02) Sensor Connection



So, as procedure, we check continuity / resistance (Ohms) on de-powered, or unpowered circuits. Ignition OFF, and key not in ignition.

1: Set multimeter to check for Continuity / Resistance. At the 02 sensor harness side, check heater connector continuity of the cold heater element at the 02 sensor wire harness.



2. Set multimeter to check for Continuity / Resistance. Volvo 240 LH-Jetronic harness side connector for continuity / resistance to ground. Alignment 'nub' up, ground is the right side electrical contact. Dunno where the ground wire for the heater side terminates. Maybe someplace near or around the wire harness under the dash around the two ECUs?



3. Set multimeter to check for Continuity / Resistance. Volvo 240 LH-Jetronic harness side connector for continuity / resistance to power through 1992 Volvo 240 #4 fuse. Alignment 'nub' up, ground is the left side electrical contact. As I've checked all wire harness connections, connectors, and such, this is the resistance in Ohms result I got. Probably through the fuel pump. (On my 1990 240 DL li'l red wagon.)



4. Set multimeter to check for Volts DC. Turn engine on. Be safe about it. Check DC volts at LH-Jetronic side 02 sensor heater connector postive volts DC. Alignment 'nub' up, ground is the left side electrical contact.



5. Set multimeter to check for Volts DC. Test 02 sensor behavior.



So, try that. If you find fault with the 02 sensor heater function, post the results back here.

Happy Friday.

Questions?

Hope that helps.

MacDuffy's Tavern.
--
Jonathan Harshman Winters III: The Mightiest, Greatest, & Most Powerful North American Comedian & Comedic Actor in Perpetuity