Fuel Gauge Needle way off
#1
03-05-2017, 07:13 AM
Fuel Gauge Needle way off
Hello Everyone,
My Dad has a 04' gmc sierra and the fuel gauge is almost half a gauge past full. Is there any way to reset these things or is it totally a sending unit issue? Of course the sending unit is attached to the fuel pump right?
Thank you
Later
My Dad has a 04' gmc sierra and the fuel gauge is almost half a gauge past full. Is there any way to reset these things or is it totally a sending unit issue? Of course the sending unit is attached to the fuel pump right?
Thank you
Later
#2
03-05-2017, 09:22 AM
*Moving to Gen Chat* since this is a question not related to the S-series trucks.
You first have to determine if the gauge itself reads correctly. A bi-directional scan tool like a GM Tech 2 or aftermarket Snap-On or AutoEnginuity scan tool can command gauge positions as well as display the reading from the sender in the tank. If the sender is reading appropriately on the scan tool and the gauge cannot be commanded to the appropriate positions, then I would suspect the gauge to be at fault.
I have seen a loose gauge needle a number of times in the past. The needles just push onto the shaft of the gauge servo and for whatever reason they sometimes pop off the shaft enough to loosen up. This could be checked without a scan tool by filling the tank, removing the clear cluster bezel, and with the key on move the needle to the full mark on the gauge then press it firmly onto the shaft. Key-off and make sure that the needle falls to its rest position, then key-on again and ensure that it goes through it's full sweep. If it doesn't go to its rest position with key-off or through it's full sweep immediately after key-on, then you could have a problem with the servo in the cluster which is also a somewhat common thing on the nnbs trucks.
Good luck!
You first have to determine if the gauge itself reads correctly. A bi-directional scan tool like a GM Tech 2 or aftermarket Snap-On or AutoEnginuity scan tool can command gauge positions as well as display the reading from the sender in the tank. If the sender is reading appropriately on the scan tool and the gauge cannot be commanded to the appropriate positions, then I would suspect the gauge to be at fault.
I have seen a loose gauge needle a number of times in the past. The needles just push onto the shaft of the gauge servo and for whatever reason they sometimes pop off the shaft enough to loosen up. This could be checked without a scan tool by filling the tank, removing the clear cluster bezel, and with the key on move the needle to the full mark on the gauge then press it firmly onto the shaft. Key-off and make sure that the needle falls to its rest position, then key-on again and ensure that it goes through it's full sweep. If it doesn't go to its rest position with key-off or through it's full sweep immediately after key-on, then you could have a problem with the servo in the cluster which is also a somewhat common thing on the nnbs trucks.
Good luck!
#4
03-06-2017, 08:05 AM
In the 2004 Sierra the PCM reads the resistance across the sending unit in the fuel tank. The PCM then sends class 2 serial data on a completely separate circuit to the instrument cluster. The instrument cluster reads the serial data and then moves the needle accordingly.
40 ohms at sending unit = empty
250 ohms at sending unit = full
Traditionally open circuits in sending unit circuit are a cause for a fuel gauge far above full. However, this system is supposed to drive the gauge to empty position if it detects such an open so that seems to be a wild card.
FYI the signal from the sending unit to the PCM is on the purple wire CKT1589. I guess I would try jumpering it to ckt470 (see below) at connector C302 and see if the gauge goes to empty, indicating that the wiring and PCM and instrument cluster are responding in some way to the input. If you suspect the sending unit, you can check the resistance with a digital multimeter, and it should be within the indicated range. If it is within range, it's not the problem.
At that point, you really need to be able to know what the computer is seeing (using a scanner), in order to truly diagnose further.
Dash Command (that you have) will display what the PCM is seeing for fuel level - but you will have to buy the 2004 GM PIDS to do this as the PID is a GM one. Alternatively you can also do this on the 2004 with Torque Pro for $5.95 or with Car Gauge Pro for $8.95. Nice thing about the two latter softwares is they don't make you buy years of PIDs ala carte for each vehicle. If I remember correctly the reason why we went to Dash Command was so you could specifically display cam sensor retard on your 1996 or 1997 Blazer (Car Gauge Pro would not do any GM PIDS on your year of Blazer). I find all of these three apps useful in some way.
Hope this info helps. I happen to have the 2004 schematics because my 2004 Avalanche is just a luxury version of the Sierra pickup.
40 ohms at sending unit = empty
250 ohms at sending unit = full
Traditionally open circuits in sending unit circuit are a cause for a fuel gauge far above full. However, this system is supposed to drive the gauge to empty position if it detects such an open so that seems to be a wild card.
FYI the signal from the sending unit to the PCM is on the purple wire CKT1589. I guess I would try jumpering it to ckt470 (see below) at connector C302 and see if the gauge goes to empty, indicating that the wiring and PCM and instrument cluster are responding in some way to the input. If you suspect the sending unit, you can check the resistance with a digital multimeter, and it should be within the indicated range. If it is within range, it's not the problem.
At that point, you really need to be able to know what the computer is seeing (using a scanner), in order to truly diagnose further.
Dash Command (that you have) will display what the PCM is seeing for fuel level - but you will have to buy the 2004 GM PIDS to do this as the PID is a GM one. Alternatively you can also do this on the 2004 with Torque Pro for $5.95 or with Car Gauge Pro for $8.95. Nice thing about the two latter softwares is they don't make you buy years of PIDs ala carte for each vehicle. If I remember correctly the reason why we went to Dash Command was so you could specifically display cam sensor retard on your 1996 or 1997 Blazer (Car Gauge Pro would not do any GM PIDS on your year of Blazer). I find all of these three apps useful in some way.
Hope this info helps. I happen to have the 2004 schematics because my 2004 Avalanche is just a luxury version of the Sierra pickup.
Last edited by LesMyer; 03-06-2017 at 08:52 AM.
#6
03-06-2017, 11:05 AM
I see some PIDS you can pull into diagnostics. Car Gauge Pro notoriously can give you PIDs that don't work along with the one that does - you have to figure out which one to use. I think some could be for different GM vehicles or even Ford. I would pull the following PIDs into a Diagnostic display all at once and see if any return responses that make sense. You will need to be connected to your vehicle via 'Powertrain" and have scanned for PIDs in order to do this.
Fuel Gauge Volts
Fuel Tank Volts
Fuel Gauge Control
Fuel Tank Level Remaining
Fuel Tank Level Remaining %
If you need me to, I'll figure it out on my Avalanche. No big deal. Let me know.
Fuel Gauge Volts
Fuel Tank Volts
Fuel Gauge Control
Fuel Tank Level Remaining
Fuel Tank Level Remaining %
If you need me to, I'll figure it out on my Avalanche. No big deal. Let me know.
Last edited by LesMyer; 03-06-2017 at 11:13 AM.
#8
03-06-2017, 11:59 AM
I found this:
"YES, In 2004 GM switched from the OLD EMPTY-40ohm FULL-250ohm to the Opposite. EMPTY-250ohm FULL-40ohm".
Per the schematic that is not true, but if it is - then that shoots down the open circuit in feed to sending unit idea that I had, and changes that to a potential short. Just keep that in mind if things end up backwards to what is expected.
Just see what you PCM thinks the gauge should be reading using the scanner. Now I'm interested.
"YES, In 2004 GM switched from the OLD EMPTY-40ohm FULL-250ohm to the Opposite. EMPTY-250ohm FULL-40ohm".
Per the schematic that is not true, but if it is - then that shoots down the open circuit in feed to sending unit idea that I had, and changes that to a potential short. Just keep that in mind if things end up backwards to what is expected.
Just see what you PCM thinks the gauge should be reading using the scanner. Now I'm interested.
Last edited by LesMyer; 03-06-2017 at 12:05 PM.
#10
03-06-2017, 02:51 PM
Okay, here are the results...
Fuel Gauge (level) Volts 1.25
Fuel Tank Volts 1.43
Fuel Gauge Control 81.2%
Fuel Tank Level 22.2
Fuel Tank Level % 9.4
It seems like while I was checking all of this, the gauge kinda reduced the amount of over compensation. It was still way over but when the key was off it was back around 3/4 full.
Fuel Gauge (level) Volts 1.25
Fuel Tank Volts 1.43
Fuel Gauge Control 81.2%
Fuel Tank Level 22.2
Fuel Tank Level % 9.4
It seems like while I was checking all of this, the gauge kinda reduced the amount of over compensation. It was still way over but when the key was off it was back around 3/4 full.
