Volvo 850 Made from 1993 to 1997, this Volvo line was available in both a wagon and a sedan, both with were graced with several trim levels.

Lamda sensor problems

Old 11-18-2018, 08:17 AM
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Join Date: Nov 2018
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Default Lamda sensor problems


I have a Volvo 850 95 model with a bad lamda sensor (O2 sensor). I have fault code 521 blinking on the diagnostic unit. I bought a new one, which is not a Volvo orginal. When I connect it everthing seems right the first 60ish seconds and then the problems starts. When the engine idles it goes down to 500 rmp and it does not sound good at all. I tried to drive but that is pretty much impossible, no power when i put my gas pedal down.

I have identified all 4 wires, two for the heater, signal and gound (4 in total) and have tested it with propane flame and multimeter. Everything seems ok, I get aprox. 1V out on signal and 13 V to the heater. The fault code also disappear after a reset. The resistance between the heater cables are 8 ohm. The new sensor did not come with connector so I just cut the connector from the old one and attached it and I am 99 percent sure it is connected correctly.

The big question is why is it not working properly? Has the original lamda sensor from Volvo other specifications?

Hopefully someone here knows what is wrong, and can help me.

Old 11-18-2018, 08:11 PM
Join Date: Mar 2012
Location: Ridgefield, CT
Posts: 4,775

the O2 sensors are pretty generic. Over the years I used a Bosch 4 wire splice in, Walker after-market all with no issues. the 521 code maps to a P0135 which points to the heating element. One of the leads should see voltage the other should be low impedence to ground. Did you try measuring ground and voltage at the connector? you could have a crossed wire or you could have a problem upstream in the wiring or connector.
Old 11-19-2018, 01:58 AM
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Everything checks out when I measuring it. If other people have successfully connected non original sensor and gotten it to work, the problems is probably located elsewhere After I connect the new sensor the fault code disappear. The signal form the new sensor has been measured to approx 1V then using a propane torch. Maybe the signal from the sensor never reach the processing unit.
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