Check engine light and battery

Is it possible for a faulty battery to cause check engine light to come on and also give a P0420 (catalytic converter problem)?

Not likely. If there were a problem with the battery that effected the engine management system, there would be more than one code stored. Including one that indicated that the battery was disconnected. And the charging system warning light would also come on.

So that code P0420 is real.


So I thought, the check light and emission workshop was on for the past 3 months but then my battery died last week and had to buy a new one. Since then, check engine light and emmsion workshop which usually came on when i drove about 5mph is gone. I have driven about 90 miles since then and still not had the light back on.
Suppose I go to auto zone to rescan, will they be able to get the P0420 although check light is no longer on.?
Also if converter is bad shouldn’t light be back on by now, i don’t want to go repalce converter for $700 if it not an issue. Thanks a lot for you rinsight.


The code P0420 means that the catalytic converter circuitry and components (oxygen sensor, egr valve, combustion process) need to be troubleshot. A shop which uses the code to tell you that the catalytic converter needs replacing, without any proper troubleshooting, just wants to sell you a catalytic converter (or, they’re just ignorant).
If the check engine light is not on, a scan won’t show a trouble code.

Disconnecting the battery clears the computer and resets the CEL. If it stays off, count your blessings and drive on.

When it comes to batteries that are nearing the end of their useful life on modern automobiles, I would not rule out the possibility of any electrical system symptom. In reading forums like this one, I have read numerous accounts in which the first symptom of a failing battery or corroded battery terminals was something obscure, such as odd CEL codes or door locking problems or computer-controlled automatic transmission problems due to erratic system voltage.

[b] the check light and emission workshop was on for the past 3 months [/b]

You do know that it is usually easier and cheaper to fix a problem when it first shows up don’t you?

Yup, and that’s why I parked the car in the garage and drove it . I only realized the light was off after i changed the dead battery