I have a 2000 Dakota 4x4 with a 4.7 engine and right at 289k for miles.

About 6 months ago, the CEL came on and it shows that the downstream O2 sensor had an issue. The mileage was fine and the truck was driving ok so I didn't worry about it. When I reset the codes, it would be fine for a while but then would show back up.

When the temps dropped, so did my gas mileage. When it was warm, I was getting close to 19. The temp dropped to 15 and so did my mileage.

I was thinking the the intake temp was bad so I mistakenly pulled the MAP sensor and used electrical cleaner on it. That was a big mistake...or maybe not.

Anyway, the truck started running like crap and it threw a code for the upstream O2 sensor, downstream O2 sensor and something else but I don't remember what now.

O'Reilly's ordered me one in but when it got here, they had the wrong part in the box. BTW, the intake air temp sensor was also misboxed. Two parts wrong at the same time...just my luck.

I had disconnected the battery again and this time the only code that I got was high voltage on the MAP sensor.

Tonight, I stopped there and got the right MAP sensor and intake temp sensor. Since it was quick, I replaced them right there.

To my surprise, there are no more codes for anything to include the downstream O2 sensor.

Are the O2 sensors tied into the MAP sensor to the point of the MAP sensor being faulty and causing the O2 codes?

 

A faulty MAP sensor will mess with you fuel mixture, therefore the exhaust will be manipulated accordingly. A factory O2 sensor only knows if your fuel mixture is right, if its lean, or if its rich.

This is why O2 sensors are good; they will tell you if somethings wrong in your engine. It can also be very expensive to fix if the O2 sensor isnt faulty, and you replace it. First sign here wouldve been both your upstream and downstream sensors throwing codes. Normally the downstreams will last alot longer than your upstreams. Your upstreams adjust your fuel mixture, while the downstreams just make sure your cats are working efficiently. The upstreams do most of the work and wear out faster. And usually, when a O2 fails, it will read that the mixture is rich. If it reads as a lean mixture, something else is wrong in the engine most likely.

Glad to hear you got it fixed though!

 

Well tonight the CEL came on again. The code was 1038...downstream O2 sensor reading slow left bank.

 

If they havent been replaced yet, at 289k it may be time. Upstreams are normally good for 100k, downstreams can longer most of the time. If its a timing error, then its most likely the O2. It could be the cat if it starts reading other error codes.