Land Rover Repair: Check Engine Light 1996 LR discovery, o2 sensor, oxygen sensor

Question
John

I bought a used 1996 Discovery SD.  The check engine light came on a few months after purchase.  I took it to the local LR dealer and they replaced the oxygen sensor, he also informed me that it was reading a "plug misfire" as well, but he thought that it could be an echo read from the bad o2 sensor.  

Six months later, I was driving and the car paused a minute, the check engine light came on again and I could tell that a plug had misfired.  I replaced the plugs and wires (I did find a fouled plug).  My little discovery started running great (and it isn't even leaving any puddles).  

However, I can't get the check engine light to reset.  I have disconnected the negative terminal connection but to no avail.

Is there a secret method of getting that light to reset without having to pay another $150 to the local dealer?  I am 99% sure that I have fixed the problem, but that little light haunts me daily.

regards,
Kevin Ledford  

Answer
Hi Kevin,

glad you were able to isolate that problem.  Did you check the OBDII reader under your passenger seat?  Is there an error code showing?  Turn your ignition key to max WITHOUT STARTING THE ENGINE...then check the code reader display.  It is about the size of a small box of crayons and has a wire attached to it.  You should be able to extend it a few inches from under the front seat.

The check engine light (CEL) usually indicates that an error has been 'trapped' and stored in a code buffer.  By removing the negative cable, you flush all codes from this buffer - a reset is performed. If the error comes back, there is something very wrong.

I know of a method to reset the SERVICE ENGINE light.  This light is used to remind us North Americans to have the LR dealer rob us blind...er...perform scheduled maintenance for emission standards, etc. (Yeah, right.)  

Here is an excellent website (with photos) that can guide you to reset the SERVICE ENGINE light.  Follow the instructions to the letter!  http://www.discoweb.org/
Go to the "Tech" button; click; find the RESET SERVICE ENGINE item on left of screen; click...read. good site too.

FWIW: resetting the CEL is usually done by disconnecting the neg cable on the battery.  Reattach cable.  With ignition, turn key to max BUT do not ignite engine.  With the ignition in the ON position, check to see if the CEL light is on.  Also check the OBDII display unit under the passenger seat.  Any codes?

IF not..  turn the engine over...wait for the CEL to return, then check OBDII.  Come back to me with a followup question and give me the code value that is being displayed.

Best of luck,
JohnMc