Engine miss/ O2 sensor?


#1

99 Tahoe, 350 vortec, 190k miles. Has 3 codes. 0305 cyl misfire. Has 0135 O2sensor bank1/sensor 1 heater performance. And 0430 cat efficiency. Seems to me O2 code means sensor itself is bad, vs sensor reading a hi/lo mixture issue? Vortec has 2 cats. Not sure if each cat has O2 sensor or single sensor after cat? Am considering buying Tahoe. Very clean, good tires, newer trans, but motor has miss. Seller has receipts for $8900 in repairs over last 7yrs. I do like the $2200 trans job. Truck shifts fine


#2

No way an O2 sensor can cause one cylinder to misfire.
Look at the plugs. Swap coils if possible. Do a compression test.
The protocol is to deal with the codes from low to high.
First check for a blown fuse to the O2 heater
Check the O2 heater with an ohmmeter at the sensor terminals.
If it’s not open you’ll need to check for presence of heater voltage at the sensor


#3

#5 is bank 1. O2 sensor is on bank 1. Don’t know if 0430 cat code is for bank 1? I know each bank has single cat. Is there another O2 sensor after y-pipe?


#4

This truck has the good old 5.7 liter with a distributor and the “spider” fuel injection

I believe P0430 is for bank 2 . . . the passenger side

Once you’ve ruled out plugs and wires, it might be good to do an injector balance test. In addition to your fuel pressure gauge, you’ll need a fairly capable scan tool . . . Snap on, Tech 2, Mastertech, etc.

You might have a partially plugged fuel injector poppet

In regards to that oxygen sensor heater code . . . in my experience, it’s usually the sensor itself that is the problem, because it has a heater circuit built in. If the heater is getting voltage, the sensor is bad. Very common. Some scan tools even show you how many amps each sensor heater is drawing. A real time saver, in my opinion. Of course, you should make sure the connector is properly plugged in, and rule out rodent damage first.


#5

“The protocol is to deal with the codes from low to high.”

This means you need to fix P0135 first, then P0305; P0430 may disappear on its own.


#6

Repair list has $393 charge for “injector” in 2010. Maybe that means it has new spider assy? There is a $700 charge for gasket? And 2-3 fuel pump charges. Might be plug, wires, or distributor?


#7

I kind of doubt $393 is enough for a spider, diagnosis, labor, etc. at a shop

It might be, if the parts were aftermarket, and the shop labor rate was pretty low, say $60/hr


#8

The system has an oxygen sensor in front of each cat converter (called an “upstream” sensor) and an oxygen sensor in back of each cat converter (called a “downstream” sensor). That’s how the system determines which “bank” has the bad converter. That’s a total of four oxygen sensors.

The P0430 code is for bank 2. P0420 would be for bank 1.

The advice you’ve received is all good. I just wanted to explain that because you’d asked and it didn’t seem to be clarified in any of the replies.


#9

yes, i see the comment to fix issues. fix miss, replace o2 sensor. i am assuming bank 1 has poor exhaust stream due to extra unburned fuel, but is bank 2 cat eff code just a 2nd, unrelated issue? the “H” pipe, after cats is not shown. it does have single bung. both cats/pipes can be bought separately. bout $130 online


#10

Cavell, the second cat converter in the other exhaust stream MUST have a downstream oxygen sensor to meet D.O.T. requirements. Both cat converters are required to be monitored. It’s just not shown on the pipes in the photo. I’m sure it’s in the next pipe I the exhaust stream.


#11

We have these same trucks at work

Yes, both cats have downstream sensors


#12

o2 sensor fitting on 1 pipe