Fuel gauge issue after fuel pump P0463

[Bow_Tied]

Hi Folks,

'06 Denali SWB, 139k km / 86k miles.

I have searched and read most of threads here and some at the old site relating to fuel gauge and P0463. Issue started with a fill up and fuel gauge dropping to E, eventually recovering after some driving. P0463 level sensor high input set. Gauge re-zeros on shut-off. Sounded like the typical level sensor problem solved by replacing it.

It's winter here so I took to a shop and had the pump replaced. He said the electrical connections all appeared in decent shape. They did have to replace the main fuel connector at the pump assy just above the tank as it broke on removal (expensive fitting btw) but otherwise was a routine job.

Got it back, fuel light still on, but I had the tank near empty for the repair so I went and put $20 in (4.8 gallons). Gauge didn't move from E and the P0463 didn't go away. Codes cleared by my scanner and P0463 returned.

Very recently I am getting P0050/0155 Bank 2 sensor 1 O2 heating circuit. I presume that is unrelated but I mention it in case.

I have dropped the truck back off at the shop for a second look but have to wait until tomorrow. Talked with the tech, younger guy who seemed genuine. I guess this time I will pay for the diagnostic fee, sigh. Any thoughts or suggestions?

Ready to sell the damn thing, breaks faster than I can fix it.

 

[Mooseman]

I'm thinking a ground or wiring issue. If the fuel pump connector/wiring was farked, maybe the one of the sender was too.

For the O2 sensor, it could just be bad. Take it from me, that one (bank 2 sensor 1 (right) side is a bitch to change to reconnect it. Recommend snipping the wires and splicing (really!).

 

[Bow_Tied]

The diagnostic was that the connectors and grounds were good and voltages at the connectors are all as expected. "Possibly the PCM, might want to take to a dealer". FML

 

[Mooseman]

PCM is not very likely. The connector maybe but not the PCM itself. It either works or it doesn't and it has its own internal checks so it would throw a code.

 

[Bow_Tied]

So - not a competent shop issue perhaps. lovely. I don't paying for work done, but paying twice irks me.

 

[budwich]

I do believe that the fuel level sender can be "read" via ohm meter to see if it is responding to changes, certainly adding $5 of gas during the "testing" would have been prudent.

It would be very unusual for the PCM to have issue with its end (ie. internal electronics) for this particular function.... and further that the connector at the pcm to have issue... potentially, wiring along the route maybe... but again checkable. The dealer will be your "friend" after this one...

PS. I am somewhat "suspicious" of the "voltages and grounds at the connectors are all good"... hmmm what exactly was tested and at exactly what connectors?

 

[budwich]

there appears to be some info from the GMSI
"quote"...
#PIT3208D: 4WD Inoperative Erratic Fuel Gauge SIR Light Service Stability Message - keywords 4.2L 5.3L ABS C0186 C0196 C0327 C0455 case communication connector inop IPC LH6 lamp light P0452 P0453 P0461 P0462 - (Jun 19, 2007)

A vehicle may exhibit: 4WD inoperative, SIR lamp, erratic fuel gauge operation and/or a Service Stability Message. Possible DTCs are C0186, C0196, C0327, C0455, P0452, P0453, P0461, P0462, P0463, P0464 and or U1088. A possible cause of these symptoms is a loose connection or backed out terminal(s) at the C101 connector, a 38-way connector mounted along the under hood fuse block. This harness may be routed tightly around the UBEC that could induce any of the concerns listed...... "end quote"

BUT... depending on how much money you want to spend, I would certainly do a few more "measurement tests" before heading in the "direction" stated above especially IF no one was under the hood when the problem first showed up.

Further the P0463 is a short to voltage of the signal circuit... this should / would be relatively easy to check.... I hate winter too... :-(
My guess is the "connectors LOOK good" is done with "poor eyes"... my "eyes" can't see electricity... a meter is your friend.

 

[budwich]

one last point before the new year celebrations are here.
It is likely that when they did their testing for voltages on the signal lines, that the vehicle was NOT running, but was in KEY ON. IF that was the case, then potentially any voltages that might have "jumped" from say the fuel pump circuit were not there as the pump wasn't running.... maybe. Of course, without knowing exactly what and how they tested, my "guess" is just that.
Also, depending on what the replacement "kit" was... some require "wire splicing", which may be an issue.

 

[Bow_Tied]

Thanks for the tips. The tech mentioned the voltages he checked at each pin out and said they were within spec - I didn't record the details. They measured the old fuel pump and said it seemed to be working properly. So I kept it lol.

 

[budwich]

:-( To me, that means they did "nothing"... first, since you weren't complaining about any "running issues" and they changed out the fuel pump why... did they not check that it ran fine? Next, the actual issue hopefully you asked them to address, was not addressed. :-( Hopefully, the new year will come with better news.... I hate "dash lights"...

 

[Bow_Tied]

I realized I failed to follow up on this. Spolier alert: My own cheapness was the author of my demise.

The shop I had do the work I had been to before for very small things and emissions testing simply because they were close to my house but I don't usually deal with them for major work as I already have a good relationship with another shop near my employer - who said "we don't do fuel tanks stuff due to insurance costs". I was annoyed, but figured a fuel pump swap should be reasonably routine to take elsewhere.

So I called the shop near my house. $769 for the fuel pump assy plus install/taxes (well over $1k total). I asked if they'd install a pump I supplied and they were fine with that but would not warranty the part, fair enough. This is where I went wrong. I picked up an AC Delco pump assy from a local supplier that I often buy parts from for $376. I was clear to specify a AC Delco fuel pump assy for a 5.3L SWB Denali. I also double checked the p/n on the web. Everything checked out. I never took it out of the box. (Failure on my part). Took that the shop and they installed it - and that's the background that led to the first post.

After the work described in previous posts I eventually put my tail between legs and went to dealer prepared to spend big bucks on whatever issue it turned out to be. I was honest about the work that been attempted. The advisor called me and says everything checks out, computer harnesses etc. so the problem must be in the tank but that didn't make sense since I had put in a Delco pump. We got talking while he was tapping on the computer and then he asks what fuel pump part number I had purchased. I didn't remember, but I said that I had indeed bought the assembly. He then says which assembly? Floored, as that was not a question I was asked at the parts store, I inquired. There are two "assemblies" one with a filter sock and one with a level sensor. And you can guess which one I didn't get.

So, I apparently gave a fuel pump assy to the other shop that had no level sensor assy on it. The tech who removed the old pump and installed the new one, somehow, didn't notice I guess that there was no level sender. Yet he tested the pump etc. supposedly.

Luckily the GM dealer treated me well and found a level sensor and installed that for me and I was on my way. Wasted a lot of money at the first shop, lesson learned.

Hope my story helps someone someday.