Fuel gauge stopped working, replaced FSU - still nothing
02-21-2018, 03:45 AM
#1
Fuel gauge stopped working, replaced FSU - still nothing
Here is my story. A few months ago, after filling up the full tank I got "Check fuel system" warning and my gauge was showing zero. Then a few miles later I got CEL and the code was P0463. I reset it, then it came back right away. I spent the evening at the forum, reading about this issue, especially for earlier C6 vettes. I tried a few treatments of Techron and Lucas oil without any success.
The behavior is always the same: when I have full tank, my gauge shows zero, I get the message about fuel system and CEL. After around half of the tank is gone (meaning that right tank is empty), the fuel gauge starts working and CEL does not come back up (if I reset it). Everything works fine until I fill up the tank. Then, I start getting CEL and gauge stopes working until half of the tank is gone. If I get only 5-7 gallons at a time (thus no fuel in the right tank), everything works fine.
Based on the above, I have concluded that FSU in the right tank went bad. I bit the bullet, purchased new FSU, removed the tank (it was a nightmare, I have auto C6), changed FSU, put the tank back. I filled the car up and I am getting the same behavior.
I did check the new FSU before putting it back and it was showing the expected range of 40-250 Ohms depending on the position of the float.
I tried resetting the CEL, removing the negative cable from the battery for > 30 mins without any success.
Any suggestions on what else could be going on? The car is 2011. I am a loss of what the next steps could be.
Sorry, did not realize I was posting this in General discussion section, I meant to post it in Tech and it does not allow me to move the post to the Tech. Hopefully, I will still get some replies.
The behavior is always the same: when I have full tank, my gauge shows zero, I get the message about fuel system and CEL. After around half of the tank is gone (meaning that right tank is empty), the fuel gauge starts working and CEL does not come back up (if I reset it). Everything works fine until I fill up the tank. Then, I start getting CEL and gauge stopes working until half of the tank is gone. If I get only 5-7 gallons at a time (thus no fuel in the right tank), everything works fine.
Based on the above, I have concluded that FSU in the right tank went bad. I bit the bullet, purchased new FSU, removed the tank (it was a nightmare, I have auto C6), changed FSU, put the tank back. I filled the car up and I am getting the same behavior.
I did check the new FSU before putting it back and it was showing the expected range of 40-250 Ohms depending on the position of the float.I tried resetting the CEL, removing the negative cable from the battery for > 30 mins without any success.
Any suggestions on what else could be going on? The car is 2011. I am a loss of what the next steps could be.
Sorry, did not realize I was posting this in General discussion section, I meant to post it in Tech and it does not allow me to move the post to the Tech. Hopefully, I will still get some replies.
Last edited by Denny79; 02-21-2018 at 04:42 AM.
02-21-2018, 07:53 AM
#2
Safety Car
Member Since: Dec 2006
Location: Pearland / Houston Tx
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I believe P0463 is the DTC for the Fuel Level Sensor 1/primary/left tank sender. Maybe should have replaced both while you had it out.
This is my thread from awhile back that I gave info on how the senders work together. Might help. My right sender went bad so I found a way to add a toggle switch with resistors to act as a sender. Didn't want to do the A6 tank drop. I figure I will eventually have the cracked fitting gas smell problem and will drop the tanks and replace everything while in there.
https://www.corvetteforum.com/forums...68-issues.html
This is my thread from awhile back that I gave info on how the senders work together. Might help. My right sender went bad so I found a way to add a toggle switch with resistors to act as a sender. Didn't want to do the A6 tank drop. I figure I will eventually have the cracked fitting gas smell problem and will drop the tanks and replace everything while in there.
https://www.corvetteforum.com/forums...68-issues.html
02-21-2018, 09:39 AM
#3
Race Director
"I believe P0463 is the DTC for the Fuel Level Sensor 1/primary/left tank sender. Maybe should have replaced both while you had it out.
Really sorry a mistake of this magnitude was made, it'd really **** me off royally w/ only myself to blame. In my case for being penny-wise & dollar foolish.
Upside's having done this before important lessons were hopefully learned making the 2nd time a good deal easier.
02-21-2018, 11:36 AM
#4
Thank you for the replies! I did read about the resistor fix and a few other threads before starting the work. I thought the Code P0463 is fuel level sensor circuit high output, it doesn’t say whether it is left or right, am I missing something?
The reason I thought it was the passenger side is since the gauge works normal when I have less than half a tank, which means that driver side tank sensor is sending correct resistor level while passenger (empty) tank sends the resistance level corresponding to the empty tank.
The reason I did not open the left tank is that I did not take it out, I removed only the right tank.
The reason I thought it was the passenger side is since the gauge works normal when I have less than half a tank, which means that driver side tank sensor is sending correct resistor level while passenger (empty) tank sends the resistance level corresponding to the empty tank.
The reason I did not open the left tank is that I did not take it out, I removed only the right tank.
Last edited by Denny79; 02-21-2018 at 11:37 AM.
02-21-2018, 02:00 PM
#5
I gave it some more thoughts, the only way I think the sensor in left tank is at fault is if it gives wrong resistance when the tank is full (for example it goes out of range). In this case, as soon as the level in the left tank drops below this critical value, I would start getting normal gauge reading.
To check if this is the case, I would need somehow to get resistance reading from the left tank when both tanks are full. If the resistance is out of range, this would mean the problem with the left tank.
To check if this is the case, I would need somehow to get resistance reading from the left tank when both tanks are full. If the resistance is out of range, this would mean the problem with the left tank.
02-21-2018, 06:47 PM
#6
Burning Brakes
find a tuner or someone who has hp tuners software. with that software, you can tell the computer to ignore trouble codes. have them turn the fuel sending unit codes off. your gas gauge will start working again.
years back, mine had the same issue. tried several "easy" fixes( techron, ect...) with no luck. changed my tune to ignore those trouble codes and have never had a gas gauge issue since.
BTW, never replaced sending units.
years back, mine had the same issue. tried several "easy" fixes( techron, ect...) with no luck. changed my tune to ignore those trouble codes and have never had a gas gauge issue since.
BTW, never replaced sending units.
02-21-2018, 07:07 PM
#7
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DTC P0463: Fuel Level Sensor 1 Circuit High Voltage
Circuit/System Description
The primary fuel level sender and the secondary fuel level sender changes resistance based on fuel level. The engine control module (ECM) monitors the signal circuits of the primary fuel level sender and the secondary fuel level sender in order to determine the fuel level. When the fuel tank is full, the resistances of both fuel level senders are low and the ECM senses a low signal voltage on both the signal circuits of the primary fuel level sender and the secondary fuel level sender. When the fuel tanks are empty, the resistances of the fuel level senders are high and the ECM senses a high signal voltage. The ECM uses the signal circuits of the primary fuel level sender and the secondary fuel level sender in order to calculate the percentage of remaining fuel in the tank. The ECM sends the fuel level percentage via serial data circuit to the instrument cluster in order to control the fuel gage.
Conditions for Setting the DTC
• The primary fuel level sensor voltage is greater than 3.5 volts.
• The above condition is present for greater than 24 seconds.
Action Taken When the DTC Sets
• The fuel gage defaults to empty.
• The driver information center (DIC) displays the FUEL LEVEL LOW message.
• The ECM records the operating conditions at the time that the diagnostic test fails. The ECM displays the failure information in the Failure Records on the scan tool.
Conditions for Clearing the DTC
• The DTC becomes history when the conditions for setting the DTC are no longer present.
• The history DTC clears after 40 malfunction-free warm-up cycles.
Circuit/System Testing
Ignition OFF, disconnect the harness connector at the primary fuel level sensor.
Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal 4 and ground.
⇒ If greater than 1 ohm, test the low reference circuit terminal 4 for a short to voltage or an open/high resistance. If the circuits tests normal, replace the ECM.
Ignition ON, install a 3A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 4. Verify the scan tool Fuel Level Sensor Left Tank parameter is less than 0.45 volt.
⇒ If greater than the specified value, test the signal circuit terminal 1 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
If all circuits test normal, perform the fuel level sensor component test before replacing the primary fuel level sensor.
Component Testing
Ignition OFF, disconnect the harness connector at the primary fuel level sensor.
While sweeping the primary fuel level sensor through its full range of motion, test for a minimum value less than 41 ohms and a maximum value greater than 119 ohms of resistance between signal terminal 1 and the low reference terminal 4.
⇒ If not within the specified range, replace the primary fuel level sensor.
Circuit/System Description
The primary fuel level sender and the secondary fuel level sender changes resistance based on fuel level. The engine control module (ECM) monitors the signal circuits of the primary fuel level sender and the secondary fuel level sender in order to determine the fuel level. When the fuel tank is full, the resistances of both fuel level senders are low and the ECM senses a low signal voltage on both the signal circuits of the primary fuel level sender and the secondary fuel level sender. When the fuel tanks are empty, the resistances of the fuel level senders are high and the ECM senses a high signal voltage. The ECM uses the signal circuits of the primary fuel level sender and the secondary fuel level sender in order to calculate the percentage of remaining fuel in the tank. The ECM sends the fuel level percentage via serial data circuit to the instrument cluster in order to control the fuel gage.
Conditions for Setting the DTC
• The primary fuel level sensor voltage is greater than 3.5 volts.
• The above condition is present for greater than 24 seconds.
Action Taken When the DTC Sets
• The fuel gage defaults to empty.
• The driver information center (DIC) displays the FUEL LEVEL LOW message.
• The ECM records the operating conditions at the time that the diagnostic test fails. The ECM displays the failure information in the Failure Records on the scan tool.
Conditions for Clearing the DTC
• The DTC becomes history when the conditions for setting the DTC are no longer present.
• The history DTC clears after 40 malfunction-free warm-up cycles.
Circuit/System Testing
Ignition OFF, disconnect the harness connector at the primary fuel level sensor.
Ignition OFF, test for less than 1 ohm of resistance between the low reference circuit terminal 4 and ground.
⇒ If greater than 1 ohm, test the low reference circuit terminal 4 for a short to voltage or an open/high resistance. If the circuits tests normal, replace the ECM.
Ignition ON, install a 3A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 4. Verify the scan tool Fuel Level Sensor Left Tank parameter is less than 0.45 volt.
⇒ If greater than the specified value, test the signal circuit terminal 1 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
If all circuits test normal, perform the fuel level sensor component test before replacing the primary fuel level sensor.
Component Testing
Ignition OFF, disconnect the harness connector at the primary fuel level sensor.
While sweeping the primary fuel level sensor through its full range of motion, test for a minimum value less than 41 ohms and a maximum value greater than 119 ohms of resistance between signal terminal 1 and the low reference terminal 4.
⇒ If not within the specified range, replace the primary fuel level sensor.
03-05-2018, 07:47 PM
#9
Fixed it!
Thanks everyone!
Just to update on this story, hopefully this will help someone. I checked the resistances of both FSU units when the fuel gauge was at zero and at normal operation. I indeed found out that when the left tank is full, the left FSU is sending infinite (open) resistance. The right FSU is normal. If I pump out a little bit of gas out of the tank (remaining around 7 gallons), the left FSU shows around 40 Ohms and progressively reduces to 250 Ohms when I remove more gas from the left tank. That explained everything. I removed the FSU and found out that the contact pins were somehow bent and when the floater at highest position the pins no longer touch the contacts. I replaced the FSU in the left tank and everything works fine now.
P.S. It was much easier doing it second time around, all in all took less than full day (including diagnostics) and I was taking my time to make sure everything is put together as supposed to be.
I may post somewhere else some tricks I learned on the way. This job is not as indimidating as it might look, even on an automatic transmission (I did not remove the cross-member but dropped the H-pipe).
Just to update on this story, hopefully this will help someone. I checked the resistances of both FSU units when the fuel gauge was at zero and at normal operation. I indeed found out that when the left tank is full, the left FSU is sending infinite (open) resistance. The right FSU is normal. If I pump out a little bit of gas out of the tank (remaining around 7 gallons), the left FSU shows around 40 Ohms and progressively reduces to 250 Ohms when I remove more gas from the left tank. That explained everything. I removed the FSU and found out that the contact pins were somehow bent and when the floater at highest position the pins no longer touch the contacts. I replaced the FSU in the left tank and everything works fine now.
P.S. It was much easier doing it second time around, all in all took less than full day (including diagnostics) and I was taking my time to make sure everything is put together as supposed to be.
I may post somewhere else some tricks I learned on the way. This job is not as indimidating as it might look, even on an automatic transmission (I did not remove the cross-member but dropped the H-pipe).
Last edited by Denny79; 03-05-2018 at 07:49 PM.
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