98 V70 Troubleshoot Cat Converter

jomustard · Post by **jomustard** » 14 May 2014, 03:12

Hi
We have a 98 V70 Wagon. Previously a OBD11 code came up PO140. We erased the code. Drove about 300 miles. Then it started losing power and stalling. My husband thinks it is the cat converter. He started taking it apart. The tip of the o2 sensor in front is pure white. The tip of the o2 sensor in back is sucky black. Is that an indication that the cat is bad? Thanks for any help. Joanne

jomustard · Post by **jomustard** » 14 May 2014, 03:14

ALso have another question...does the wire unplug from the o2 sensor or is it one unit? Thanks

Post by **abscate** » 14 May 2014, 05:02

The plug is up in the engine bay, jus t follow the wire until you find it.

That code usually means the second O2 sensor has failed. It will not affect driveability, it is just a monitor. The fact that your car started stalling means you have another problem you need to troubleshoot.

jomustard · Post by **jomustard** » 15 May 2014, 15:20

Thank you abscate!

Post by **Ozark Lee** » 15 May 2014, 18:15

Normally when a catalytic converter goes bad it comes apart internally and it sounds like it is full of gravel if you give it a smack with your hand. The real test is a back pressure test which can be done by a muffler shop.

As Abscate said, the P0140 code usually indicates either a failure of the oxygen sensor or its associated wiring.

...Lee

Post by **JDS60R** » 15 May 2014, 20:49

In 1998 the rear sensor is more than a monitor. It is the final fuel trim. Cats do fail and the hammer test is an easy way to test if the internal ceramic brick has melted down. It is the right first step.

In order for a cat to not be efficient (95% or greater) it is failing to perform its designed function by using its bonded elements ( platinum, palladium and rhodium) to heat up and process the exhaust gasses into a more acceptable chemical combination. These catalyst fail usually due to failed oxygen sensor, over-fueling or oil contamination , that goes untreated, and causes its death. There are other,less common reasons like poor wash coating,physical contact etc

If both o2 sensors were not changed at 100K intervals or sooner the cat has likely failed.
Use a non contact thermometer and measure the front weld bead temp and the rear while running. The rear will be significantly hotter.

here is a video to help explain.

It is a good idea to try new Bosch sensors first if the sensors are past 100K miles in use. You can always move them to the new cat if this does not solve you issues.

Please do not spend money on a cat until you have fixed your upstream air/fuel issues ( or new cat will fail just like its predecessor).
Ignition must be strong and all sensors should be checked for operation and accuracy. ( Clean MAF, new plugs, put car on OBD2 scanner and check temps and readings to see if all sensors and fuel trims are within normal range. )

If a new cat is needed I suggest magnaflow brand with new Bosch oxygen sesnors. Magnaflow has just released new downpipes with cats in them and they can be had for aprox $350 if you shop around. If you car has always been cat code sensitive buy the California certified converter from Magnaflow.( usually an extra $100

Post by **rmmagow** » 16 May 2014, 11:32

So JDS, on a 98 always do both sensors then? My 217K V70 AWD is probably ready and all I initially bought was the front one, I'll get a rear one too then. No codes yet but a welded in used Volvo cat is in use now. Occasional rotten egg smell, don't know if it's me or cars in front of me but....

Post by **JDS60R** » 16 May 2014, 14:32

Yes both sensors need to be replaced - rotten egg is sulfur from running too rich.
If your at 217K with original sensors I would be concerned with damage done to current converter due to length of time with worn sensors.

You can just call me John or JD. The S60R part is just one of my cars.