Possible ground issue

[Double0Redneck]

Recently I had to do a complete engine build on a 2015 6.2 LT in a Yukon Denali for a broken valve spring resulting in a dropped valve. Since getting it back in the road I've had a few electrical gremlins. Mainly throwing a P0420 catalyst low efficiency code that wasn't there before the new engine but showed up immediately after. I found this ground wire loose today. It bolts to the front of the block on the driver's side right above the vaccum pump, just under the number 1 spark plug. There looks to be 3 or 4 ground wires in this bundle. Does anyone know what these grounds are for? TIA

 

[OR VietVet]

I have no idea what the grounds are for but I am assuming you checked for cleanliness and corrosion and then tightened them down and cleared the code and drove and did the CEL/code come back?

 

[Double0Redneck]

I have no idea what the grounds are for but I am assuming you checked for cleanliness and corrosion and then tightened them down and cleared the code and drove and did the CEL/code come back?

I did remove the bolt and checked the connectors for corrosion and replaced the bolt and tightened it down. I cleared the pending codes but have not driven it yet.

 

[OR VietVet]

I did remove the bolt and checked the connectors for corrosion and replaced the bolt and tightened it down. I cleared the pending codes but have not driven it yet.

You may have fixed it and not know it yet. Please drive and report back. I hope/assume you did inspect the grounds at back of engine close to firewall?

 

[Double0Redneck]

You may have fixed it and not know it yet. Please drive and report back. I hope/assume you did inspect the grounds at back of engine close to firewall?

Yes, those grounds are good. They were reconnected when I put the new engine in, along with the ground connected to the a/c compressor bracket and to the passenger side of the block just ahead of the starter.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[SpyShops212]

When I replaced my engine in my 2008 the check engine light came on. The code was for oxygen sensor. I replaced all 4 OEM and all was good. I didn’t have any oxygen codes before I replaced my engine.

 

[Double0Redneck]

When I replaced my engine in my 2008 the check engine light came on. The code was for oxygen sensor. I replaced all 4 OEM and all was good. I didn’t have any oxygen codes before I replaced my engine.

I may have to try that. I'm just not much on throwing parts at a problem in hopes that it cures it. Looking at live data, all 4 O2 sensors are reading voltage, from around 85mV to 900mV but it never goes into closed loop and the down stream sensors constantly fluctuate as fast as the upstream sensors.

 

[salisburyv]

well, bad grounds can cause a lot of grief. First, how many miles are on the vehicle? it is possible, due to the bad valve, that a bunch of unburnt fuel could've gotten past the cylinder and messed up the cat. How long was it run for when you suspected something was wrong? it might be a bad cat. sorry to say....

 

[Double0Redneck]

well, bad grounds can cause a lot of grief. First, how many miles are on the vehicle? it is possible, due to the bad valve, that a bunch of unburnt fuel could've gotten past the cylinder and messed up the cat. How long was it run for when you suspected something was wrong? it might be a bad cat. sorry to say....

It has approximately 115K. It had just over 114K when it dropped the valve and it ran for about 10-15 seconds before it locked up. It's actually showing codes P0420 and P0430. Dropped valve was on #2 cylinder so I could see the possibility of an issue on the right bank, but not both banks at the same time.