guys today i was cleaning the intake n i decide to clear the code p0420 by disconnecting the negative cable for 10 mins n the code didnt came back i drove for about 4 miles away from my house.... hey kurt i thinks is a coil maybe cuz the sparks where change like 2 monts ago.. how do i know if a spark is defective???? thanks for all your help guys.. i like this forum

 

the code will come back. it takes 2 'trips' for the code to reset. it will for sure. may take a week or so but it will return.

defective spark is determined with an oscilloscope or a quality scanner in misfire monitor mode.

 

well hwen i got other codes the codes came back in five minutes of driving will seee m8... you cant tell just by looking at the sparks???? how to check coils ??? can i check coils with a voltmeter?

 

My 97 is obd2 and has had the map stuck just as unsaid with no code. The first time it happened I only had a simple code reader/ reset tool so I didn't see what was wrong. It took me a bit of troubleshooting to figure it out. The second time it failed, I had up graded to a tool with monitoring and saw it stuck at 13.8 ( I think that's about where it was) even with the engine off. Each time, disconecting it would cause an engine light but the engine could at least be started in the limp in mode with it disconnected.

I have also left the idle air motor connector off accidently and it didn't trip a fault. The engine ran poor at idle and I discovered my mistake.... no fault though.

 

you need a volt meter that can read over 10,000 volts to read sparks

 

Its not your cat..you have a bad oxygen sensor, that needs to be replaced..

 

How can you say that with absolute assurance without reading O2 sensor volts?. I've seen a lot of P0420 codes and every one has a bad cat. Infact, I recently helped out a lady with a 2005 focus w/ 60,000 miles. She had a P0420. With my scanner connected I could see both 02 sensors reading perfectly, but the upstream and downstream sensors read the same values which means the cat isn't converting anymore. Since her car was under the Federal Emissions Warranty Guidelines, I had her take it to Ford, which they reluctantly replaced her cat FREE.

After the work was done, she brought me a home made apple pie with a big thanks. She showed me what the bill would have been @ $2200.

 

yeah right but everybody is telling me if the cat id faulty it would make a bad noise when i acelerate...

 

no everybody is NOT tell you that. cuz I'm somebody which would be part of everybody and i'm saying you need to have it connected to a scanner to see what the 02 sensor values are showing. this WILL determine if you need a cat or sensor but I'm going on a cat. a cat can loose it's effectiveness and NEVER make a noise nor cause driveability issues. but if you don't want to belive me, then by all means go buy new oxygen sensors and replace them.

 

well thats what happen on my moms expedition no check engine n the cat is screw... it makes an a rouglhly noise... n no check engine at all...

get in gear mecanic told the is part of emission he mean oxygent sensor... well will see...

anyways how can i test the oxygen sensro before spending some money????