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Forum > Failed Smog Test > Question

1996 Nissan Pickup Truck failed for high HC.

Vehicle failed smog. high hc 90ppm in m1 test. I know it runs rich because there were carbon deposits on the plugs when I replaced them. Vehicle sat for 5 years prior to test. New gas, new plugs, new fuel filter, new wires, replaced oil and filter . Didn't replace air filter cap or rotor. Tech thinks it's an injector or the O2 sensor. Wouldn't O2 sensor failure cause check engine light to come on? Tech checked timing. Tested OK. Is a bad injector my problem or is it something else. I should mention car had a miss across RPM range, this was fixed by wire replacement prior to test.
Answer:

Well it sounds like you've made the proper repairs to fix high HC faults except if the fault is related to a lean or rich fuel mixture; in which case the fault may very well be the oxygen sensor. The check engine light will not always turn on with a bad O2 sensor. The O2 sensor can simply be "lazy", not trigger a trouble code, yet cause improper air/fuel ratio. We'd recommend getting a fuel feedback test to ensure the O2 is working right. posted by SmogTips Support

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