2004 Suburban PCM/Fuel Level Problem

[TylerHagerdorn]

I think I posted my thoughts on one of your previous threads.

Anyways, here's a wiring diagram for an 04 with dual tank setup, although I suspect the single tank should be similar.

The fuel pump/sender has basically a variable resistor on the sender portion. It's just s ground and the purple wire as shown. The purple wire goes directly to the PCM.

You either have a wiring integrity problem or a faulty fuel sender. I know you said you recently replaced the fuel pump, but that doesn't mean the sender is bad. Does the gauge drop any after fuel level drops? I've read on other websites guys have actually posted what the resistance should range based on fuel tank level.

These threads may have useful information for you:

Stock Fuel Level Sender - PerformanceTrucks.net Forums

GMT 800 & Older GM General Discussion - Stock Fuel Level Sender - What is the stock sender ohm range? I am making a custom fuel cell for my 2002 Silverado and I'll need a sender that will work with my stock gauge on my dash. I think it's 0 ohms empty, 90 ohms full but I might be wrong.

www.performancetrucks.net

It looks like there was a change from 99-03 vs 04+? At least on the trucks? Maybe the wrong part was installed? That would definitely cause your problem because of a mis-match in calibration for the senders.

99-03 vs 04+ Fuel Level Sensor - PerformanceTrucks.net Forums

FUEL SYSTEMS - 99-03 vs 04+ Fuel Level Sensor - So to finally put any confusion to rest about the specs on the senders/sensor for the fuel level on the factory returnless vs return systems, here it is from the GM service manual: 84781...

www.performancetrucks.net

I hope this helps.

Hey strutaeng,

I've done more testing now that I know how to properly read ohms. Never had to before in my life surprisingly. Gauge is sitting couple notches under the full mark.

Here's my readings:
238 ohms
2.46 volts

According to the chart, that reads empty with the low fuel indicator on

So I'm not sure where to go from here. PCM is basically saying it's empty when the gauge is reading near full.

Im going to buy new bolts today for the two frame grounds under the door. The bolts were fine but they didn't get fully tight against the frame as they should. I don't think that's hurting it though.

I've also disconnected the battery and leaving it for about an hour. Just to "reset" the PCM. I did my testing directly at the PCM plug and at connector C152 under the fuse box. Same results in both spots. Checked the cluster connector just to make sure and there's no loose connection there.

 

[strutaeng]

Hey strutaeng,

I've done more testing now that I know how to properly read ohms. Never had to before in my life surprisingly. Gauge is sitting couple notches under the full mark.

Here's my readings:
238 ohms
2.46 volts

According to the chart, that reads empty with the low fuel indicator on

So I'm not sure where to go from here. PCM is basically saying it's empty when the gauge is reading near full.

Im going to buy new bolts today for the two frame grounds under the door. The bolts were fine but they didn't get fully tight against the frame as they should. I don't think that's hurting it though.

I've also disconnected the battery and leaving it for about an hour. Just to "reset" the PCM. I did my testing directly at the PCM plug and at connector C152 under the fuse box. Same results in both spots. Checked the cluster connector just to make sure and there's no loose connection there.

I was messing with my 04 project suburban and I was also doubting my voltages. But that one has the dual tank setup and I had a code for the secondary tank IIRC. That dual tank setup is still kinda of a mystery how it works to me. Unfortunately, I did not check resistance. The truck has sat for several years now. I added fuel and drove it and my fuel guage works again (I was getting a high voltage code.) I think the sender was just stuck.

The only thing I can think of is get yourself another fuel pump assembly (junkyard) and plug it in, play around with the sender/floater and that will tell you if yours inside the tank is bad. I saw Eric on SMA do that on a Corvette was was fixing a few months ago. Or just check resistance and compare them to the published specs on that link that I posted. The comment about getting a scanner that reads fuel level is a good idea. Maybe a friend of a friend has one?

I mentioned recently on another post about the service 4wd message on this same truck. The encoder motor range sensor was bad. I checked resistance while manual turning the wheel and the resistance was erratic.


I hope that helps, but I'm out of ideas.

 

[mattbta]

Do you know what OS # you have?

I have a 2004 Flex Tahoe that I put a Delphi FG0810 in. Post install, it would never read full, usually 6/8-7/8. At the time, my OS was basically the universal donor in the tuning world - 12587603. Would bet your's is, too.

Looking at tis2web, there was an update to the fuel calibration, which required an OS upgrade too. Now my gauge reads full. 12606960 is the new OS.
tis2web link: https://tis2web.service.opel.com/tis2web/

 

[TylerHagerdorn]

I was messing with my 04 project suburban and I was also doubting my voltages. But that one has the dual tank setup and I had a code for the secondary tank IIRC. That dual tank setup is still kinda of a mystery how it works to me. Unfortunately, I did not check resistance. The truck has sat for several years now. I added fuel and drove it and my fuel guage works again (I was getting a high voltage code.) I think the sender was just stuck.

The only thing I can think of is get yourself another fuel pump assembly (junkyard) and plug it in, play around with the sender/floater and that will tell you if yours inside the tank is bad. I saw Eric on SMA do that on a Corvette was was fixing a few months ago. Or just check resistance and compare them to the published specs on that link that I posted. The comment about getting a scanner that reads fuel level is a good idea. Maybe a friend of a friend has one?

I mentioned recently on another post about the service 4wd message on this same truck. The encoder motor range sensor was bad. I checked resistance while manual turning the wheel and the resistance was erratic.


I hope that helps, but I'm out of ideas.

Yeah I'm not dropping the tank again lol. Especially with a full tank. I know new can be bad...but in my 14 years of working on cars and in parts I've never seen a Delphi bad out of the box.

I don't know if I mentioned to you, but the issue is the PCM is reading empty via the values...while the cluster should be full but won't go all the way there. PCM is what sends the level via class 2 data. The float doesn't control the gauge like it did years ago

 

[TylerHagerdorn]

Do you know what OS # you have?

I have a 2004 Flex Tahoe that I put a Delphi FG0810 in. Post install, it would never read full, usually 6/8-7/8. At the time, my OS was basically the universal donor in the tuning world - 12587603. Would bet your's is, too.

Looking at tis2web, there was an update to the fuel calibration, which required an OS upgrade too. Now my gauge reads full. 12606960 is the new OS.
tis2web link: https://tis2web.service.opel.com/tis2web/
View attachment 410483

Mine is an FG0811. Mines a 31 gallon tank. And I'm leaning towards it needing flashed because it's just a junkyard PCM from an 04 Suburban with the same rpo codes so it works but I know it needs flashed.

 

[mattbta]

Mine is an FG0811. Mines a 31 gallon tank. And I'm leaning towards it needing flashed because it's just a junkyard PCM from an 04 Suburban with the same rpo codes so it works but I know it needs flashed.

I'm saying the updated fuel calibration fixed my Delphi pump reading less than full.

 

[TylerHagerdorn]

I'm saying the updated fuel calibration fixed my Delphi pump reading less than full.

Right I know what your saying. I was just saying the PCM in my truck is not the original one and still wears the original vin of the other truck. Because it needs flashed. And here's what searching my vin on tis2web shows.

 

[strutaeng]

I've never been able to get my fuel gauge needles on my 2006 all the way to the full mark. I just thought that's how they were. But now that remember, I did the cluster LED and maybe I installed the needle a little off. Lately I can't recall the last time I tried filling up at 37 gallons anyways.

I haven't tried on the 04.

You are correct on the fuel gauge needle being controlled by the Class 2 data, I just saw that. If the issue was only that it didn't go to the full line, I would say just pop the needle on the cluster and re-stab it on the right position.

 

[mattbta]

Right I know what your saying. I was just saying the PCM in my truck is not the original one and still wears the original vin of the other truck. Because it needs flashed. And here's what searching my vin on tis2web shows.

That page just shows available updates, you'd need a tech2 or PCM Hammer with VCX Nano to see what is actually flashed to the PCMs.

 

[TylerHagerdorn]

That page just shows available updates, you'd need a tech2 or PCM Hammer with VCX Nano to see what is actually flashed to the PCMs.

Yeah I'm looking into one. But either the dealer or a local shop with the proper software can flash the PCM to my truck and apply the updates at the same time.