Resetting The Check Engine Light

[JLG60]

My check engine has come back on. I had it at the dealer last week and the error message was P0420 Catalyst System Inefficiency. They claimed this was caused by misfiring from last time when fuel got into converter not completely burned. I bought the car (used - 87K miles) at the beginning of the month and two days later the check engine light and the trac control light were on and it ran rough. The diagnosis at that time was that a spark plug was fouled due to the steam cleaning of the engine. After replacing the plug, everything ran fine.

Now if I am to believe them, this problem should go away. However, how can I reset the check engine light myself, without taking it into the shop?

Thanks.

97 LS400 (want to be) Happy Owner

[mehullica]

Disconnect the negative battery clamp for a minute and reconnect

[lctothe3]

The other option is to take it to an AutoZone if you have one near you. They will read the error, and if you ask nice, or tell them "that you drove it with the gas cap loose" they will reset the error, or at least they do it at the store near me.

[mann777]

I suppose this topic has been talked many many times, i attaching this document by the manufacturer itself how to solve the checklight procedure. Checklight__procedure.pdf

[JLG60]

Update: Light went off last night. Did not come on into work this am. Maybe/hopefully the mechanic was correct.

[bicol-ini]

if it is intermittent it will not show up but if it is a hard code it will be stored in the ecu, so if the CHECK ENGINE comes up again get the code and trace it where it is coming from and replace the faulty part or it will just go back again, remember it is an emissions item,

[mann777]

Mostly it is the O2 Sensors that fail and that is the main cause to the Check light most of the times, Maybe you can remove the old one and refer to the lexls website for the correct ampere output from your stock car O2 Sensors and then maybe it have a change if it is below the rewuired level.

[JLG60]

Hopefully I can now close the chapter on this one. I appreciate everyone's input on this board. Well after several more times with the check eng light on for a couple of days and then off for a couple of days, the dealer sent it to a specialist who replaced the O2 sensor! I am not anticipating anymore "check engine light' issues.

[Steve Clough]

Hopefully I can now close the chapter on this one. I appreciate everyone's input on this board. Well after several more times with the check eng light on for a couple of days and then off for a couple of days, the dealer sent it to a specialist who replaced the O2 sensor! I am not anticipating anymore "check engine light' issues.

Just want to add that you can buy an OBDII code reader for as little as $60.00 (I got one for $89.00). It plugs in under your dash in the diagnostic port very similar to plugging in an old dot matrix printer with the serial port connectors. You press read codes and they come on the screen. You can erase the codes with the reader, then see if the CEL comes on again. Of course, this also precludes having to disconnect battery cables (even if you don't buy the reader, buy a quick connect terminal end for the negative cable, it saves you from needing any tools on the road to disconnect/reconnect). Many times it's a one-off situation that doesn't perpetuate. Any many times, you get a clue so you're forearmed with at least some knowledge to prevent getting taken by disreputable or non-knowledgeable mechanics.

Just a suggestion. Knowledge is power.

[curiousB]

Note time stamp on prior post. 41 months later probably isn't worth the time to post a reply. I doubt OP is actively waiting for an answer now.

[soyangelito]

I have an egine light problem too. I had the car parked for over a yer and now the engine light and "trac off" are on. Any sugestions?

[billydpowell]

sure, first, read the codes, see what they tell you, and then do a search to see what others have done... there is no blanket statement that covers a CEL..