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Should I connect a lambda sensor without a catalytic converter??


New member
Jul 5, 2021
Long story short, I have a Volvo 960 T16V, the car "hicupps" arround 3.5 rotations, of what i saw in this forum the problem is not having a lambda sensor, the car has no lambda sensor since someone stole the catalytic converter (somehow the mechanic made the lambda sensor error light disappear), i don't have money to replace the catalytic converter, does it solve the problem or make any sense to connect a lambda sensor into exhaust with no catalytic converter?
You're probably talking about the upstream O2 sensor, which doesn't require a convertor. And the ECU really does need that to get feedback on the fuel trims.

I'm not sure if you'd have OBDII in Portugal, or what year your car is, but that would have a second O2 sensor after the cat that is only used to see how effective the cat is, and set a warning light if it's not doing its job. That wouldn't (as far as I know) have any effect on how the engine runs.
First, the easy answer. There is no problem installing a lambda sensor in the exhaust stream without a catalytic converter. As long as the sensor is located approximately where it would have been with the catalytic converter in place the sensor should operate fine and correctly measure lambda.

The second question as to whether it will fix the problem is more difficult. Assuming this is the sensor that would be in front of the catalytic converter, a lot will depend on how the ECU deals with the absence of a sensor. Depending on the year and market specific designation, the ECU may have basic fatal error detection which would force the ECU into open loop fuel control because of a failed lambda sensor. If the engine was in perfect condition the engine should run just fine in open loop. However, most engines deteriorate with age and the lambda sensor's job is to correct those conditions. If your engine has aged the absence of a lambda sensor may cause some operating problems. If your ECU has no fatal error detection it may interpret the absence of voltage from the lambda sensor as a lean fuel condition. If the ECU enters closed loop control this would result in the ECU adding extra fuel to try and correct the lean condition. This will result in high fuel consumption and poor operation.

As stated by JohnMc, if this is the sensor on the outlet of the catalytic converter it will have no effect on the operation of the engine.
If you have LH2.4 expecting a narrow band o2 sensor (that would be any car with a cat from the factory) and don't have one installed it'll barely run at all.

It will be fine, but stinky, without the cat substrate.
Without the sensor fitted (not even plugged in) the system will run open loop base map, if the sensor is plugged in but dangling then the ECU with richen the fuel mixture to the max.

As the sensor is a pre cat sensor it does not matter one bit if teh cat is there or not