P0031 and P0051 CEL on
 

Hi,
I have a 2001 MVP ES with 65k miles. Recently the van had a very rough idle with multiple codes. My mechanic replaced the intake manifoldset and the idle air control motor, and now the van runs very well. (And the "sick moose call" (aka "fog horn") sound when idling is now gone...thank goodness!!)

After clearing all the codes,we keep getting the following codes P0031 and P0051 coming up at the same time. My mechanic doesn't want to immediately replace both oxygen sensors because he feels it's weird that they would have both blown at the same time. That and the fact that these parts are extremely expensive. He's afraid that he will do a $400 - $500repair and still be faced with the same problem.

Could it be anything else? What are the chances that two of four oxygen sensors would be faulty? Anyone with similar experience?

As I said, the car runs just fine, but I am being held hostage by Pennsylvania emmissions requirements. I need my inspection stickers, so the CEL must come off!

Thanks!

RE: P0031 and P0051 CEL on
 

Both codes are indicating a fault in the oxygen sensor heater circuits of both right and left bank sensors. Kind of unusual that both would fail at the same time but is a simple check to verify. Have the mechanic unplug the upstream O2 sensors and check the resistance of the heater circuit within the O2 sensor itself. Should be around 6 ohms give or take a few depending upon how hot the sensor is when checking. The heater circuit is the two black wires off of the O2 sensors. If the readings from both sensor heaters check out ok then there could be some other possible problems but would definitely start with that inspection first off.
All four Oxygensensors are supplied voltage from the same Black with White stripe wire thru the 15 Amp ENGINE fuse. A capacitor up by the front of the engine is also used in this circuit as this wire also supplies power to the coil pack. Possible that the capacitor could be failing and bleeding off too much voltage to the O2 heaters but would kind of expect downstream O2 heater circuit codes P0037 and P0057 to also set if this was the case.Should also probably be creating some ignition spark problems as the coils could not get sufficient voltage to create a good spark. Possibility anyway.

RE: P0031 and P0051 CEL on
 

Thanks, BabyHuey! I really appreciate it. We ended up replacing the O2 sensors, and everything seems to be fine. CEL is now off for the first time in months. Still need to drive it for 100 miles or so before we can test emissions.

Thanks again!

UGH!! P0051 would be Bank 2 Sensor 1, which is in front of the Radiator.. It isn't all that hard to get to. Just remove the battery, take the battery tray out, then you can get to the connector right under those few hoses, kinda a tight squeeze there but it can be done. and ofcourse you will need the o2 sensor socket to get it out, because of the tight area you have to work with in there.

Happy Fixing.

I know this is an old thread how do we remove the same upstream 02 sensor in the back bank one closer to the firewall? I have the same codes. I hope someone reads my post and help me. There is no relay or fuse for the heater for the 02 sensor I gather from the responses.