Picture of the downstream O2 sensor location? (1 Viewer)

[amongmany]

I have a code P0037 showing up that indicates the Bank 1 downstream O2 sensor. Planning to swap both for good measure. Anyone have a photo of the location so I know where to look?

Also, can anyone confirm the part numbers? I ordered these, but I noticed that the upstream part numbers are different (makes sense). Just want to confirm I have what I need before I start working on it.

 

[jiggletits]

Just look under your truck. It is pretty obvious where both are located. They’re the only sensors attached to the exhaust. ‘Bank 1’ means the same side as ‘cylinder 1’ which is the front-most cylinder and I believe is on the drivers side. Upstream is before primary cat, downstream is after. Hence the name ‘upstream’ and ‘downstream’.

If you can’t find these on your own you should not be attempting DIY.

No sense in changing both downstream o2 sensors, waste of money. They don’t do much. It is your upstream sensor that adjusts fueling, that one is WAY more important. Downstream only monitors cat efficiency.

You’ll need an o2 sensor socket or a very nimble and secure ⅞” wrench. If it is stuck and you strip it you are f’d so be careful.

 

[amongmany]

Just look under your truck. It is pretty obvious where both are located. They’re the only sensors attached to the exhaust. ‘Bank 1’ means the same side as ‘cylinder 1’ which is the front-most cylinder and I believe is on the drivers side. Upstream is before primary cat, downstream is after. Hence the name ‘upstream’ and ‘downstream’.

If you can’t find these on your own you should not be attempting DIY.

No sense in changing both downstream o2 sensors, waste of money. They don’t do much. It is your upstream sensor that adjusts fueling, that one is WAY more important. Downstream only monitors cat efficiency.

You’ll need an o2 sensor socket or a very nimble and secure ⅞” wrench. If it is stuck and you strip it you are f’d so be careful.

Fair, I see the drivers side no problem. Wasn't seeing the passenger on immediate inspection.

 

[HomersCanyonero]

I think there’s a slight part number difference on my 2003 compared to other years but I can’t remember for sure…

 

[amongmany]

I think there’s a slight part number difference on my 2003 compared to other years but I can’t remember for sure…

I watched that video. it's for the upstream sensors. As I understand it, P0037 indicates a downstream sensor issue.

 

[Rednexus]

FYI, be careful ordering O2 sensors from Amazon. Fakes Denso sensors abound on there and on eBay. I'd suggest getting them from Rock Auto, Summit Racing, or another reputable online seller.

Also, the downstream sensors can be easily replaced with Denso universal 4-wire sensors. The universal part number is 234-4209. They are the same as the OEM sensor, but simply lack the OEM plug. You'll need to cut the OEM sensor harness off between the plug and sensor and use some heat-shrink butt splices to join the OEM plug to the new sensor. It's like a 5-10 minute job per side and can easily save you $100 or more. I've actually found it faster than trying to mess with unhooking the OEM connector. The downstream sensors are located in the midpipe, between the exhaust manifolds and the catalytic converter. They are easy to access with an open end wrench. I think they are either 19, 21, or 22 mm but don't recall exactly. You don't need an O2 sensor socket for them.

I recently replaced my 15-year old upstream sensors and have noticed much more stable fuel trims and performance. Bank 2 always used to be richer than Bank 1, now they are the same. O2 sensors are a wear item and often get lazy after 100K, even if the vehicle seems to be running fine.

 

[amongmany]

FYI, be careful ordering O2 sensors from Amazon. Fakes Denso sensors abound on there and on eBay. I'd suggest getting them from Rock Auto.

Also, the downstream sensors can be easily replaced with Denso universal 4-wire sensors. They are the same as the OEM sensor, but simply lack the OEM plug. You'll need to cut the OEM sensor harness off between the plug and sensor and use some heat-shrink butt splices to join the OEM plug to the new sensor. It's like a 5-10 minute job per side and might save you $100.

I recently replaced my 15-year old upstream sensors and have noticed much more stable fuel trims and performance. Bank 2 always used to be richer than Bank 1, now they are the same. O2 sensors are a wear item and often get lazy after 100K, even if the vehicle seems to be running fine.

Are those the correct denso part numbers for the downstream sensors if I weren't going with the universal ones? Or are these the universal?

 

[Rednexus]

Are those the correct denso part numbers for the downstream sensors if I weren't going with the universal ones? Or are these the universal?

The part number I provided is for the universal sensors. I do not know if the senors you linked are correct for direct-fit sensors with the OEM plugs. I would suggest verifying the part numbers using the Rock Auto online catalog if you don't want to use the much cheaper universal sensors.

 

[amongmany]

The part number I provided is for the universal sensors. I do not know if the senors you linked are correct for direct-fit sensors with the OEM plugs. I would suggest verifying the part numbers using the Rock Auto online catalog if you don't want to use the much cheaper universal sensors.

Ah, I missed the part number. Thanks.

 

[Rednexus]

Ah, I missed the part number. Thanks.

No problem, I was editing my post to include it while you were replying .

If you go universal don't use the provided connectors. Use real heat shrink connectors like this:
Amazon product ASIN B07Q3JJRY8
You can heat shink them using a lighter for a heat gun.

 

[amongmany]

No problem, I was editing my post to include it while you were replying .

If you go universal don't use the provided connectors. Use real heat shrink connectors like this:
Amazon product ASIN B07Q3JJRY8
You can heat shink them using a lighter for a heat gun.

The denso parts I have listed in the OP are for the correct, non-universal sensors verified by rockauto. I have them in hand already.

 

[HomersCanyonero]

I watched that video. it's for the upstream sensors. As I understand it, P0037 indicates a downstream sensor issue.

Ah, yes, the upstream ones were harder to reach than the downstream ones.

I did order the same ones you posted for downstream Denso 234-4260 and 234-4261

 

[OllieChristopher]

FYI, be careful ordering O2 sensors from Amazon. Fakes Denso sensors abound on there and on eBay. I'd suggest getting them from Rock Auto, Summit Racing, or another reputable online seller.

You beat me to it. This cannot be stressed enough. I was lucky to only get fake Oral B toothbrush heads to learn my lesson. Spark plugs are another big one. That being said good luck to getting your O2 sensors sorted.

 

[OllieChristopher]

And put some anti seize on the threads before installation.

 

[amongmany]

Got them done this morning. Thanks for the help folks.

 

[HomersCanyonero]

Let’s hope that fixes your issue! Seems straight forward