O2 Sensor(s)

ruddy · October 16, 2007

I have a '96 GMC K1500 with the 5.0L engine that has 120K miles on it. The gas mileage has fallen off, and the check engine light comes on under load (like pulling a boat trailer) but goes out after the load is removed. I figure it's probably a good idea the replace the oxygen sensor, but I don't know much about them. My Chilton and Haynes manuals don't tell me specifically what kind or how many I have.

Can you help me out here? Can you recommend a good source for them?

Thanks.

ChevyTech007 · October 16, 2007

Do not just start replacing O2 sensors. You will be wasting money. Have it scanned for codes, then post back.

luminaapv3 · October 16, 2007

page 6-16 to 6-17 in the haynes manual tells you all about them, even has pictures.

your truck should have 4 of them, 2 before the catalytic converter and 2 after it.

I checked autozone and they are listing them at $70 - $100 bucks each!

I would suggest that you do what ChevyTech007 suggested and get the codes before you start spending $300 - $400 on something you don't need, then post back and we can help you better.

Autozone will read the codes for you for free.

ruddy · October 17, 2007

page 6-16 to 6-17 in the haynes manual tells you all about them, even has pictures.
your truck should have 4 of them, 2 before the catalytic converter and 2 after it.

My Haynes manual for 1988 thru 1998 pickups mentions a (one) O2 sensor on pages 6-9 and 6-11. The Chilton manual for 1988-96 full-size trucks talks about one or more that may be single- or triple-wire units. That's why I'm asking. I've heard that the Schucks auto parts stores around here will also read the codes for you. I'll give that a try tomorrow. My check engine light isn't on, so I don't know if anything will show up.

Thanks.

luminaapv3 · October 17, 2007

heres what my haynes manual says on page 6-17 (left side first paragraph a few sentences down):

"Early models (1988 through 1995) are equipped with a single wire O2 sensor mounted in the exhaust pipe after the exhaust manifold.

Late models (1996 through 2000) are equipped with four oxygen sensors; two pre-conveter oxygen sensors and two post-converter oxygen sensors. The pre-converter O2 sensor is mounted in the exhaust system before the catalytic converter...........

Also on late model O2 sensors, the post-converter O2 sensor (mounted in th exhaust system after the catalytic converter) has no effect on PCM control of the air/fuel ratio. The PCM uses these sensors to monitor the efficiency of the catalytic converter."

I found that sometimes Haynes produces newer, same manuals with more info in the updated manual, maybe this is the case with yours.

As for the single wire or triple wire sensors, just locat the sensors in the exhaust system and look at the wires, you will plainly see if they are single or triple wire units. Just replace the sensor with the same one.

Get the codes first, then worry about changing things, so you don't waste money.

ruddy · October 18, 2007

I stopped by an Autozone store, and they couldn't find any stored codes. I guess I'll have to get a code reader, so I can catch one during one of the infrequent times my check engine light comes on. Any suggestions for a code reader?

ruddy · October 22, 2007

I stopped by an Autozone store, and they couldn't find any stored codes. I guess I'll have to get a code reader, so I can catch one during one of the infrequent times my check engine light comes on. Any suggestions for a code reader?

Yesterday I was carrying enough of a load for my "Service engine soon" light to come on while I was accelerating up a slight hill. Fortunately I was near an Autozone store so I could get a reading. The code was "MAF" which is for the $133 air flow sensor. The technician, however, thinks it's more likely caused by the O2 sensors between the manifolds and the cat. He said they would cause the intermittent service light indications, while a MAF sensor failure would trigger the light continuously. He suggested replacing the two $55 O2 sensors. He also said that 120K miles is a long lifetime for these sensors and they're due to be replaced anyway.

The light was on this morning when I started the truck, but it went out before I cleared the driveway.

What do you all think?

ruddy · October 23, 2007

Anyone?

ruddy · October 24, 2007

My MIL came on again yesterday as I was driving to work, so I thought I'd stop at a Schuck's store on my way home. Unfortunately, the light went out on the way to the store. I talked to a parts counter employee, and he suggested trying to clean the MAF sensor. He also did not agree with what the Autozone guy told me.

After doing some Google research about cleaning these things, I get the impression that using K&N air filters is not a good idea because some of the filter oil gets on the sensor wires. I do have one, and it was recently cleaned and re-oiled. I'm thinking that replacing it with a factory type filter and cleaning the sensor would be the way to go. I am also getting an OBD II code reader, so I can monitor what's going on.

Any other suggestions?

ruddy · October 29, 2007

I obviously didn't get a solution here, but I thought somebody may benefit from my experience. I ran across this post to another forum, and it led me to the answer: http://www.obd-codes.com/forums/608-obd-co...-silverado.html

I did what was suggested, and it solved my problem. The truck runs better and has noticeably more pep off the line. I'm glad I didn't follow the advice I got at the Autozone store.