1996 Volvo 850 High NOx Emissions

VOLVO 850
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TOOTSIE
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1996 Volvo 850 GLT failed NO (PPM) test. Limits at 15 MPH are Max 430, Average 57. Measured at 534. Everything else passed otherwise. Mechanic replaced spark plugs & battery. He now wants to change the catalytic converter. Could this have been the problem? We have put quite a bit of money trying to get the darn car to pass smog already.
May 30, 2006 at 8:26 AM
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2CARPRO JACK
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Nox is exhaust temp.......... be sure the egr system works if so equipped...... if not could be a mixture problem(lean) try oxygen sensors the go to the Mass Air Flow Meter
Sep 12, 2006 at 10:35 AM
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Suggested Repair

Before replacing the catalytic converter, verify the EGR system works if the car is equipped with one. If EGR is not the cause, check for a lean mixture by testing the oxygen sensors, then the mass airflow meter.

Conversation Summary

A 1996 Volvo 850 GLT failed the NOx portion of an emissions test at 15 MPH (534 PPM versus a 430 PPM limit) while other readings passed. Spark plugs and the battery were already replaced, and the mechanic proposed a catalytic converter. The expert said high NOx relates to exhaust temperature and advised confirming EGR operation if equipped, then checking for a lean mixture via the oxygen sensors and mass airflow meter.

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