CarTalk.com Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

93 Honda Civic: CA Smog test fail related to dead battery?

My 93 Civic just miserably failed its smog test. The HC was slightly high and the NO was more than double the allowable limit. The car has just over 100K miles.

Last week, I had a dead battery and since then, I’ve only driven the car 10 or 15 miles, tops. I’ve read that when the battery dies and the computer resets, that can cause such failures, but this post seems to indicate that this is only true of cars made after 1996: http://community.cartalk.com/discussion/2213598/failed-ca-smog-test-due-to-coputer-reset

Could the computer reset be the problem with my 93 too? Or am I up a creek?

Any ideas or advice would be much appreciated!

Do or did you have any check engine lights or warnings?

Nope, no lights, no warnings, no problems whatsoever really. So far as I can tell, it runs just fine.

It may work differently based on vehicle year, but I think that your battery problem could be related to the test result. However, it seems that the smog tech should have told you, or asked if you had disconnected your battery (or had a dead battery) very recently. I took my 96 Caravan for a CA smog test immediately after installing a battery, and according to my smog tech, he couldn’t test it until I’d driven fifty or so miles. Or maybe what he really meant was that it would fail if he did…that subtle point was not made clear. He just told me to go drive it 25 miles down the highway and come back, maybe stop somewhere along the way and shut off the engine for a few minutes. I presume it had to do with storing data in the computer. That’s what I was told, I don’t know how accurate it is. You might ask the tech to clarify this. Hope this helps.

Your car was made before OBDII was mandated so it is unlikely that the dead battery had anything to do with it. If you are overdue for an oil change, that could have caused you to fail the HC, otherwise you probably need new spark plugs or maybe a new oxygen sensor.

The high NOX reading suggests that the EGR system is plugged up, which would be common for a car with 100k miles on it. The EGR valve may be plugged or one of he ports feeding it is carboned up.

Before you pull into the inspection station, its a good idea to get out on the freeway and run a few miles to get everything warmed up, never go in with a cold engine.

Thanks for the information.

I am overdue for an oil change (almost took care of it yesterday!) so I’ll hope that’s the reason for the HC and will get it taken care of before I go back in.

This model (the SI) doesn’t apparently have an EGR (according to the manual, only the VX had it that year). I grabbed a new O2 sensor and am going to hope that that fixes the problem (assuming I can install it without screwing something else up). The car wasn’t really warmed up when I took it in, so I’ll make sure to take it for a spin before I try again.

How’s your air filter? If you haven’t replaced that in a long while, replacing it may be some help, though probably not the reason for the fail. It’s the low hanging fruit.

BTW, has your fuel mileage been as good as normal? Usually a bad O2 sensor takes a big hit on mileage.

I went through this with my 1993 Chevrolet Caprice at it’s last NJ emissions inspection. The O2 sensor on the 93 is a two wire and is not heated. If the Caprice idles for any length of time it goes into open loop mode. I am posting a link to the thread I started on the subject.

Ed B.

The dead battery can’t cause high readings. On newer models, the computer may show “not ready status” for some of the systems but that’s all. Some states might fail that and some won’t.

High HC could indicate too rich of a fuel to air mixture or a bad catylitic converter among other things. The NOX coud be related to ignition timing. A mechanic is going to have to investigate.

In addition, an oil change isn’t going to do anything to correct the HC reading.

An oil change can affect the HC reading. I don’t quite know how to describe this, but the longer the oil is in the engine, the rate of breakdown increases and when it breaks down, it is recycled through the combustion process by the PCV system. That adds a small amount to the HC readings. Fresh oil does not burn as fast.