Sunday, April 16, 2006

Tip #7 Testing catalytic converter (CAT) codes

As mentioned before, oxygen sensor installed after the CAT is used to monitor the converter’s condition. Whenever the CAT is plugged or contaminated, the oxygen sensor will give a code which reflects its efficiency. If you get a code (like low efficiency) for this CAT oxygen sensor, here are the best strategies for repairs:

Check the oxygen sensor first. Check the sensor wiring connections for burns and proper contact. You can follow it up with probing the voltage readings. If you recall, the normal oxygen sensor upstream oscillates from 0.1 to 0.9 volt after the engine gets hot. However, the CAT oxygen sensor voltage reading variation is actually smaller between 0.4 to 0.7 volt or a difference of 0.3 volt. Also, if you monitor both upstream and downstream oxygen sensors from cold, the voltage reading will be almost the same but as soon as the engine gets hot, the variation starts to show up.

If the CAT oxygen sensor reading is stuck or non-existent, it probably shows the CAT is defective but you can start the repair by replacing the oxygen sensor first. If after replacing this sensor and condition remains the same, it’s time to change your CAT.

Shown below is an example of a CAT oxygen sensor:


When replacing your CAT, try tapping the body with a rubber mallet. If there is noise inside, it shows the CAT has deteriorated.

Stay away from after market and cheap CAT unless you are prepared to do it again. (Always use the CAT from the dealer).


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