Catalyst Efficiency

My 1996 GMC Sierra's OBDII Light was on...it was a bad sensor and bad heater element in bank 1 sensor 3. So, Naturally, I replaced it...but now after about 50 miles the OBDII light came on again....this time:

P0420
Catalyst Efficiency Below Threshold


The Cat I have on there is less then 3 years old......


sadly, the guys at Advance, Autozone, and Napa have no idea what this code means exactly...

Any suggestions?

need more history on your vehicle ...

have you had any fuel problems recently?

have you ever done a tune-up? If so, what did it include?



My 1996 GMC Sierra's OBDII Light was on...it was a bad sensor and bad heater element in bank 1 sensor 3. So, Naturally, I replaced it...but now after about 50 miles the OBDII light came on again....this time:

P0420
Catalyst Efficiency Below Threshold


The Cat I have on there is less then 3 years old......


sadly, the guys at Advance, Autozone, and Napa have no idea what this code means exactly...

Any suggestions?

I had a tune up last year (ish) it included plugs, wires, rotor button, distributer, dist. cap.

I havent had any fuel problems...but for 1-2 years I was having issues with the spark. Basically, I was replacing the wires, plugs, rotor button, and dist cap every 6 months. It seems to have cleared up though.

While I was having spark problems, my OBDII was reading a "multiple mis-fires" code.


I changed my fuel filter also.


I can say this though.....My fuel pump went on the fritz...so I changed it. But now the fuel guage reads normally..until 1/4 tank...then it bounces back to full..and stays there until the tank is empty.

three things ...

have you ever changed your pcv valve? easy to do ... should change it with the plugs. Costs about $3

next,

have you ever cleaned your throttle body? if not, go to Autozone and get Throttle Body cleaner. $3 -- clean it.

next,

check your ignition coil: at nite, is it arcing? sparking? -- also, is there white crusty crud around the coil?

do a search on this forum and/or other GMC forums on "arcing" "coil" etc ...

report back after doing this. "Catalyst Effeciency" code is probably your cat but lets see if these cheap things (TB clean, PCV) don't help first .





I had a tune up last year (ish) it included plugs, wires, rotor button, distributer, dist. cap.

I havent had any fuel problems...but for 1-2 years I was having issues with the spark. Basically, I was replacing the wires, plugs, rotor button, and dist cap every 6 months. It seems to have cleared up though.

While I was having spark problems, my OBDII was reading a "multiple mis-fires" code.

I changed my fuel filter also.


I can say this though.....My fuel pump went on the fritz...so I changed it. But now the fuel guage reads normally..until 1/4 tank...then it bounces back to full..and stays there until the tank is empty.

I kept getting the same light.

It would come on about once every month and then continued with shorter intervals until it was coming on about every other day.
I wanted dual exhaust so when I took it in the guy said the light was my cats needing replacement.
I looked at my old cats after they were off and they were almost all clogged up.

I was surprised it ran at all!

It wasn't cheap, but it runs MUCH better and mileage inproved a little bit.

98 GMC Z71 5.7

FYI

ive got a 98 z71 5.7 duals from the front right out the back....i knocked all the crap out of the cats to get straight flow thru and kept getting the same light p0420 and p0430 bank 1 and bank 2....truck ran like crap ....left it that way for months...found out that summit and jegs have a part for this "OFF ROAD USE ONLY" of cource.....POST-CAT SENSOR SIMULATORS....tells the ECU cats are working even though there are none.....light never came back on ran it thru the scan tool and everything came back READY.....truck even got faster and stronger when towing........get this .....even passed inspection since its a 98 or later they plug up to the OBD II port.......sorry so long....hope it help.......the part was $88.00 with next day ups