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Why did my Volvo 940 Fail The Smog Test?

93 Volvo 940 failed the smog emissions only. I got diagnosis and replaced parts. It failed again, barely.

After the smog diagnostic the smog technician said my Volvo's O2 sensor and catalytic converter were bad. I went ahead and replaced them and got a re-test, and it failed again barely at 25MPH. I took the Volvo back for diagnosis this time they said the timing sensor is not reading/working right. The oxygen sensor and CAT are fine. I have no idea what is going on with this car and could really use some advice! Thank you very much!!! :)

Answer:

The ignition timing sensor could be an issue, along with a host of other potential issues. The bottom line is you're going to need an experienced smog technician to diagnose your Volvo's smog check failure all the way to smog check passing status. Some times finding the root cause of high emissions can be difficult. On older vehicles with emission components ready to quit, even harder. The smog tech ends up replacing smog parts which appear and for the most part are defective, only to find additional barely functioning sensors and/or solenoids which need replacement also. Often it is not apparent a certain component requires replacement until after a pre-component has been replaced/repaired. Passing the emissions test requires all the smog components on your Volvo 940 be working together and properly. posted by SmogTips Support

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