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Shouldn't their be a recall on this issue.
My 2009 C6 with 40K miles has the same issue.
Everytime I fill my tank always with Chevron premium my gauage drops to 0, low fuel warning beeps and then the DIC displays Service fuel system. Then ofcourse the engine light comes on.
After about 3 cycles the engine light goes out and my fuel gauge pops to full about 24hrs later.
I add Techron to my tank about once per month and I still have these issues.
*** GM SHOULD RECALL FUEL SENDING UNITS.****
Shouldn't their be a recall on this issue.
My 2009 C6 with 40K miles has the same issue.
Everytime I fill my tank always with Chevron premium my gauage drops to 0, low fuel warning beeps and then the DIC displays Service fuel system. Then ofcourse the engine light comes on.
After about 3 cycles the engine light goes out and my fuel gauge pops to full about 24hrs later.
I add Techron to my tank about once per month and I still have these issues.
*** GM SHOULD RECALL FUEL SENDING UNITS.****
My 08 is doing the same thing. After filling the tank the needle drops to empty. Rocking the car while driving seems to make it come back after a few miles. I'm assuming it is the sender unit in the right tank that is the culprit, since the left pump was replaced already due to the leaking fuel issue. I put in two bottle of Techron a month or so ago, but that hasn't stopped it from happening. It seems to work ok once I use some gas out of the tank and it drops below the full mark. I'm assuming that the top end of the stroke on the potentiometer in the right sender has some corrosion or sulfates built up on it, and causes an open circuit due to a dead spot on the potentiometer.
My 08 is doing the same thing. After filling the tank the needle drops to empty. Rocking the car while driving seems to make it come back after a few miles. I'm assuming it is the sender unit in the right tank that is the culprit, since the left pump was replaced already due to the leaking fuel issue. I put in two bottle of Techron a month or so ago, but that hasn't stopped it from happening. It seems to work ok once I use some gas out of the tank and it drops below the full mark. I'm assuming that the top end of the stroke on the potentiometer in the right sender has some corrosion or sulfates built up on it, and causes an open circuit due to a dead spot on the potentiometer.
My '05 started doing these a few months ago. Once I burn off about 1 gallon all goes to normal. I set my trip odo just in case. Annoying, but not a couple $K annoying.
I think that this problem should be a recall by GM as part of the smog system warranty. In California I cannot smog my car if the MIL light is on because of the fuel sensor. I suspect that it has something to do with the EVAP system, since the PCM will not test the EVAP system unless it meets certain parameters. Temperature being one, and the other fuel level. GM does not test the EVAP if there is more than 85% fuel in the tank or less than 15% fuel in the tank. An error in the fuel tank sensors likely prevents the PCM from testing the EVAP and therefor sets the MIL.
Here are some photos of the condition of the sending unit contacts from my passenger side tank. You can see why adding Techron won't do any good to fix this. You'll have to pull the tank and replace the sending unit.
This worked for me!!! I was a little skeptic of cutting into my factory harness considering I just purchased my vette. But I needed the emissions done and my cel kept going on and off so I decided to give it a try and sure enough it worked!!! Passed with flying colors!!!
So I recently did this little hack and it did the trick for me...until now. I was able to pass emissions which bought me some time. My problem came back and I’m trying to figure out why. I replaced the resistors hoping for some reason they failed but if you guys have any ideas where I should start or why it may have stopped working. Because in theory even if I replace the fuel sending unit it still wouldn’t work because there’s 250 ohms going to it right now with the resistors right?
What were the values of the two resistors you used? The PCM on 2005 and 2006 will she the right hand tank empty when the PCM measures 1 volts across the fuel sender resistor. 2007 and later the PCM was reprogrammed to see the right track as empty when the PCM measures 2.57 volts. So for a 2005-2006 if one resistor is 100 ohms, the other resistor needs to either be 4 times that value On mine I used a a 100 ohm (connected to the PCM) and a 400 ohm resistor (connected to ground) so the PCM would measure 1 volts across the 100 ohm resistor, which is empty on the right track on my 2006. If you have a 2007 and later model the PCM need to measure 2.57 volts You can use a 220 ohm and 190 ohm resistor or use a voltage divider calculator on the web to find other resistor combination as long as you use 5 volts for input voltage and the output voltages is 1 volt for 2005-2006, or 2.57 for 2007 and later.
Last edited by peterpeter211; 03-27-2019 at 12:52 AM.
What were the values of the two resistors you used? Seems that the PCM on all of the models will show empty when the PCM measures either 1 or 4 volts across the fuel sender resistor. My 2006 is 1 volt, and I saw that the 2007 is 4 volts. Either way the same resistors will work. So if one resistor is 240 ohms, the other resistor needs to either be 4 times that value or 4 times smaller (240/60 ohms or 240/960 ohms). On mine I used a a 100 ohm (connected to the PCM) and a 400 ohm resistor (connected to ground) so the PCM would measure 1 volts across the 100 ohm resistor, which is empty on my 2006. If your model need to measure 4 volts, then the PCM connects across the 400 ohm resistor and the 100 ohm resistor connects to ground.
Thanks for the reply. This terminology is a bit of a foreign language for me just based on the original post I used a 220 ohm resistor and a 33 ohm.
Your resistors combination (220 and 33 ohm) are not the correct values. When the troubleshooting manual says to read 250 ohms across the fuel sensor, it is only giving to you the resistance across one half of the fuel sensor potentiometer used by the PCM. GM does not give you the resistance across the other half of the fuel sensor (Although everyone asks me for it)
When the system is working correctly, on a 2005-2006 model, the PCM will measure 0.99 volts across half of the fuel sensor when the right tank is empty
On 2007 and later, when the system is working correctly, the PCM will measure 2.57 volts across half of the fuel sensor when the right tank is empty.
Using your resistors (220/34 ohms) the PCM will either measure a steady 0.652 volts drop across the 33 ohm resistor or a steady 4.348 volts drop across the 220 ohm resistor (huge difference from 2.57 volts). On 2005-2006, the PCM is programmed to measure a 0.99 voltage drop across the smaller value resistor when the tank is empty (0.652 volts MAY not be a problem with the 33 ohm resistor, but the 4.348 volts WILL give you a DTC for high voltage). On 2007 and later (?) the PCM is programmed to measure a 2.57 voltage drop across the fuel sensor when the right tank is empty. (Either 0.653 or the 4.348 volts WILL cause an error with the PCM).
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The resistors you are using are causing the problem because, depending on your model year, which I assume is 2007 or later, the PCM is measuring 4.348 volts across the 220 ohm resistor instead of the normal 2.57 volts for an empty tank- 1.778 VOLTS OVER THE NORMAL EMPTY TANK VOLTAGE..( A side note, I suspect the reason GM changed the sensors to read higher voltage dtop when empty in 2007 is to make it easier for the PCM to detect a bad fuel level sensor. This also makes it much more important to have the correct value resistors that will allow the PCM to measure 2.57 voltage drop when empty since 2.7(?) volts will trip the DTC for High Voltage and 2.47 volts will show fuel in the tank a trip a DTC for inconsistent fuel reading between the tanks. This is also why simply inserting a 250 ohm resistors won't work because the resistor drops the entire 5 volts, and the PCM will give a High Input DTC since it is measuring 5 volts. )
If you have a 2005-2006, and a high voltage DTC, then I suspect you wired the resistors backwards. On 2005-2006 the low value resistor connects across the two wires going to the PCM and the high value resistor connects across the wires going to ground and the wire from the PCM THAT DOES NOT READ 5 Volts. Resistors are connected in series.
On the 2007 and later it is opposite. The high value resistor connects between the wires going to the PCM and the low value resistor connects across the wires going to ground and the wire from the PCM THAT DOES NOT READ 5 Volts. Resistors are connected in series.
I recommend for a 2006-2007 (I'm not a mechanic just an electronics technician), a 100/400 ohm 1/2 watt resistor combination. (This is what I used in mine). For 2007 and later, I recommend a 190/220 ohm 1/2 watt combination or something in multiples of 10. (19/22ohms-will need 1 watt resistors;1900/2300 ohmd-will need 1/2 watt resistors).
You can find other resistor combinations using one of the voltage divider calculators on the web. Just ensure your load/output voltage is 0.99 (1 is close enough) on 2005-2006, and 2.57 volts on 2007 and later. Input voltage for all years is 5.0 volts.
Your resistors combination (220 and 33 ohm) are not the correct values. When the troubleshooting manual says to read 250 ohms across the fuel sensor, it is only giving to you the resistance across one half of the fuel sensor potentiometer used by the PCM. GM does not give you the resistance across the other half of the fuel sensor (Although everyone asks me for it)
When the system is working correctly, on a 2005-2006 model, the PCM will measure 0.99 volts across half of the fuel sensor when the right tank is empty
On 2007 and later, when the system is working correctly, the PCM will measure 2.57 volts across half of the fuel sensor when the right tank is empty.
Using your resistors (220/34 ohms) the PCM will either measure a steady 0.652 volts drop across the 33 ohm resistor or a steady 4.348 volts drop across the 220 ohm resistor (huge difference from 2.57 volts). On 2005-2006, the PCM is programmed to measure a 0.99 voltage drop across the smaller value resistor when the tank is empty (0.652 volts MAY not be a problem with the 33 ohm resistor, but the 4.348 volts WILL give you a DTC for high voltage). On 2007 and later (?) the PCM is programmed to measure a 2.57 voltage drop across the fuel sensor when the right tank is empty. (Either 0.653 or the 4.348 volts WILL cause an error with the PCM).
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The resistors you are using are causing the problem because, depending on your model year, which I assume is 2007 or later, the PCM is measuring 4.348 volts across the 220 ohm resistor instead of the normal 2.57 volts for an empty tank- 1.778 VOLTS OVER THE NORMAL EMPTY TANK VOLTAGE..( A side note, I suspect the reason GM changed the sensors to read higher voltage dtop when empty in 2007 is to make it easier for the PCM to detect a bad fuel level sensor. This also makes it much more important to have the correct value resistors that will allow the PCM to measure 2.57 voltage drop when empty since 2.7(?) volts will trip the DTC for High Voltage and 2.47 volts will show fuel in the tank a trip a DTC for inconsistent fuel reading between the tanks. This is also why simply inserting a 250 ohm resistors won't work because the resistor drops the entire 5 volts, and the PCM will give a High Input DTC since it is measuring 5 volts. )
If you have a 2005-2006, and a high voltage DTC, then I suspect you wired the resistors backwards. On 2005-2006 the low value resistor connects across the two wires going to the PCM and the high value resistor connects across the wires going to ground and the wire from the PCM THAT DOES NOT READ 5 Volts. Resistors are connected in series.
On the 2007 and later it is opposite. The high value resistor connects between the wires going to the PCM and the low value resistor connects across the wires going to ground and the wire from the PCM THAT DOES NOT READ 5 Volts. Resistors are connected in series.
I recommend for a 2006-2007 (I'm not a mechanic just an electronics technician), a 100/400 ohm 1/2 watt resistor combination. (This is what I used in mine). For 2007 and later, I recommend a 190/220 ohm 1/2 watt combination or something in multiples of 10. (19/22ohms-will need 1 watt resistors;1900/2300 ohmd-will need 1/2 watt resistors).
You can find other resistor combinations using one of the voltage divider calculators on the web. Just ensure your load/output voltage is 0.99 (1 is close enough) on 2005-2006, and 2.57 volts on 2007 and later. Input voltage for all years is 5.0 volts.
first off I GREATLY appreciate your response. I’m starting to see what you’re saying now about the output voltage. I’m going to give your method a shot my only question is since resistors are a series I want to make sure I wire them up correctly. I followed the original post by c6togo and I have a light blue wire and I think black. It’s whichever two wires in step 4 of that write up. My question for you is how to I know which wire is to the pcm and requires the higher value resistor?
I am traveling and don't have access to all of my wiring diagrams. Also I have a 2006 and don't know what is the year of your Vette.
On my 2006 there are three wires. A black and white wire that goes to ground. You can confirm this with a VOM. There is also a black wire and a light blue wire that go to the PCM. I believe the light blue wire is the 5 volts wire (check with VOM). The black wire is the reference voltage that changes with the fuel level. You can confirm the light blue wire is the 5 volts wire with a VOM with the key on engine off (KOEO). The 5 volts should be either on the light blue or black wire.
I recommend soldering the two resistors together and putting a crimp spade on each of the three resistor wires after you for the wires. The crimp spades will let you plug the resistors into the connectors.
On my 2006 I connected the one (non soldered) end of the 100 ohm resistor into the connector with the light blue wire (5 volts wire). I connected the spade with the two resistors soldered together to the black wire. Then I connected the end of the 400 ohm resistor (non soldered) to the black and white wire on the connector (ground).
If you have a 2007 and later the one (non soldered) end of the high value resistor plugs into the 5 volt wIre (light blue wire). The spade with the two resistors soldered together plug into the black wire. The end of the low value resistor (non soldered) plugs into the black and white connector (ground).
I am traveling and don't have access to all of my wiring diagrams. Also I have a 2006 and don't know what is the year of your Vette.
On my 2006 there are three wires. A black and white wire that goes to ground. You can confirm this with a VOM. There is also a black wire and a light blue wire that go to the PCM. I believe the light blue wire is the 5 volts wire (check with VOM). The black wire is the reference voltage that changes with the fuel level. You can confirm the light blue wire is the 5 volts wire with a VOM with the key on engine off (KOEO). The 5 volts should be either on the light blue or black wire.
I recommend soldering the two resistors together and putting a crimp spade on each of the three resistor wires after you for the wires. The crimp spades will let you plug the resistors into the connectors.
On my 2006 I connected the one (non soldered) end of the 100 ohm resistor into the connector with the light blue wire (5 volts wire). I connected the spade with the two resistors soldered together to the black wire. Then I connected the end of the 400 ohm resistor (non soldered) to the black and white wire on the connector (ground).
If you have a 2007 and later the one (non soldered) end of the high value resistor plugs into the 5 volt wIre (light blue wire). The spade with the two resistors soldered together plug into the black wire. The end of the low value resistor (non soldered) plugs into the black and white connector (ground).
so I gave it a crack this morning using a 510/470 ohm set up and nothing. I tried a couple other resistor combos but same result. I only have the light blue and black wires cut( as the first write up advised to) and spliced into the ground. Right now I have a p02066 code which I would assume is due to me fiddling around with the resistors and or having run it on a 220/33 ohm set up. I followed your last post exactly in terms of wiring it up the only difference we’re the resistor values. And yes you’re right I have a 2007 and I’m using 1/4 watt resistors. I don’t have a radio shack in town I have a rather large kit I purchased online but they are all 1/4 watt. Thanks again. Safe travels.
So many differences between models. Your sensor has two wires because GM saved some money by omitting a wire. The two wires are the voltage out VOUT side of the circuit. The voltage divider does not require "a separate" ground wire. Often circuits are grounded to the housing (typically a screw through the circuit board with the screw touching the second half of the potentiometer and metal on the housing), which is then grounded to the car chassis via a grounding strap. If there are two wires, then you ground the end of the second resistor to the cars chassis. This is actually called a floating ground (no pun intended).
11-27-2015, 05:00 PM
Service fuel system/ gas gauge drops to 0
