I bought an '03 Disco 2 back in August. The dealer had replaced both upstream sensors prior to me buying the vehicle. Shortly there after, also in August, I had to have both downstream sensors replaced (wasn't cheap). The service engine light came on last night, so this morning I had Auto Zone run their diagnostic test, and it's showing both downstream sensors have failed. It's only been 6 months, and I've only put 5,800 miles on it.

I understand that these O2 sensors are one of the many things that are common issues, but this can't be normal, right? I see British Atlantic has a tutorial on a DIY replacement, so I plan to do that. I just don't really want to have to do this so often.

Thanks guys

 

It will be awesome if you try the replacement yourself. Not so difficult the 2nd time. Sometimes true even after you replaced the O2 sensor it fails. It happened to me several times. Out of the box, dead. Better get them locally so when they fail whithin the guarntee period you can replace them fast than mailing it back somewhere.
I think its also about the age of our trucks which complicates the work of the new sensors, just my thought.

 

Other things cause them to fail too... Like fluids dripping on the connector... An improperly cleaned and seated installation will also lead to a failure, which can be corrected.

Try inspecting them before you buy new ones, see if there is grease or dirt inside the connector. Clean them up and use dielectric grease. Make sure the wire didn't get pinched or damaged.

I wouldn't trust a used car dealer to do the best work.

 

The sensors should last 100K miles. Do you have receipts for the work? I would be looking into a warranty replacement.

It's def a DIY repair. All you need is a $5 Oxygen Sensor socket/wrench and you can get another genuine sensor for $60 but the 1 supplied by the garage failed way too early if that's what it is.

 

Thanks guys. Yeah, I'm going to call the shop that did the work. It's a reputable place, and I think they will at least replace them at no charge. I'm just a little nervous there is an issue that may be causing them to fail. I'll update once I have more info

 

Have you been checking the coolant regularly? Does it idle roughly upon cold startup? Otherwise noticeable "stumble" @ idle thereafter? There are conditions that will ruin an oxygen sensor but you will find other faults to cause this. Let the garage that did the original work take a look and tell you if the sensor/sensors have actually failed and the cause but FYI if the garage is not willing to cover any new replacement costs, you can DIY in a couple of hours for considerably less than what they are charging. Even the markup on the parts themselves could easily be 100% and then you get to the $60-$100/hr labor fees. You can buy the genuine sensor online for $50-$60 each and nothing but a cheap ratchet, breakover bar and a O2 sensor wrench/socket.
Coolant loss via the exhaust like a compromised head gasket will ruin the front sensors but probably not even this quickly. it could also be cheap, aftermarket parts but IF there is no coolant loss or cylinder misfire then it's just a poorly manufactured part that should be replaced at no cost so be vigilant with this and don't let them screw you around.

 

What kind of sensors were installed up stream? There are at least 2 threads per week about O2 sensors failing.
If you have leaks from the valve covers ( most of us do at some point) the oil can collect on the O2 and give them a very short life span.
I went thru 4 Bosch O2 sensors all of which failed from right out of the box to 30 days later, all from AMZN.
I finally went with walker sensors from AB.
This a good first time project, but getting the sensor connection off the mounting post can be a little tricky. Take your time and thoroughly clean the connector, applying dielectric grease on the outside plastic of the male end to help keep fluids out. Good luck.

 

One important point of clarification. I went to a different auto parts store for some oil etc., and while I was there I had them run another diagnostic test just so I could be sure of which sensors were triggering the code (the first kid seemed confused by the code readout). The bad sensors are both the downstream, post CAT sensors. (I edited the OP).

I have a good relationship with the shop that did those sensors back in August, so I'm going to call them today. I will see what they think the issues is. If it's just faulty sensors and they won't cover the cost to replace them, I will definitely go the DIY route.

I do watch all the fluid levels like a hawk. Within the last few weeks it's been losing a little coolant. It's minimal, but the underside of the oil cap has a little milky coolant on it. So, I am actually planning on doing a head gasket job - probably even next weekend. I was planning on doing it this spring as a preventative measure anyway. The truck as 123k on it, so I knew that was coming up in the near future.

The exhaust looks okay though. My neighbor is a mechanic, and I had him look at the exhaust and he agreed there didn't appear to be any smoke/burning coolant. So I think the head gasket has a small leak, but at the moment it's not terrible.

 

You can get that coloration in the oil fill cap due to short trip driving in cold weather. It takes longer trips to burn out the normal condensation in there. This is normal in winter for these trucks.

You would be better off finding the source of your coolant loss first, unless you already know it is an external HG leak. Check your TBH gasket and or do a pressure test.

 

Great advice. I'm in Cleveland, Ohio, and it's definitely cold here. I called the shop, they're going to look into the O2 sensor issue and while it's there I told them to pressure test the system. I'm dropping it off tonight.

Thanks guys