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My 99 Accord’s been throwing heater circuit malfunction codes for both O2 sensors (upstream and downstream) for almost a year now. I replaced them with new ones by Bosch and got the same codes, so I swapped those out for a set of Densos thinking going back to the OEM might be the difference maker. Still got the codes. It’s also got a VTEC solenoid code and the wrong catalytic converter on the car (cat is not CARB legal). Why Oreilly sold me an illegal cat I have no idea. Not sure whether either of these could be inadvertently causing the sensor codes, but I seriously doubt it considering it’s a heater circuit malfunction rather than a misread. I’m suspecting a short or a bad connection in the harness, but I’m not sure. Ideas? ANY help is appreciated the car’s overdue on registration since I couldn’t pass smog to renew it before I left for school. Thanks
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Assuming you’ve got a four cylinder, the wiring diagram shows that your O2’s share a common power that splices somewhere farther up the harness. It should be a black/yellow wire at each of them. Get a voltmeter and see if you’ve got battery voltage at both of them to start with.
Here’s the procedure for diagnosing O2 heater codes.
Aftermarket cats don’t work on Honda’s. It’s not that they sold you an illegal cat, it’s that it doesn’t hold up to the standards Honda set for that vehicle.
As for the VTEC code, check the oil level and make sure you’re using the correct viscosity. If not, change to the correct viscosity and recheck.
Good luck and keep us posted.
Well I just bought a Magnaflow from Summit…ran me $500. Checked the part no. (#546083) with the manufacturer and on the CARB database and everything checks out. Are you saying it still won’t work and I need to buy the $900 one from Honda?
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