My 2002 C5 threw a P1431 code tonight, and the gas gauge went from just below half down to zero. I had driven 270 miles @ 23mpg since last fillup, leaving at least 6 gallons in the car. I pulled out my Tech2 clone and thought I would share my observations and readings.

Parked, the left tank sender voltage was 1.94V, and right tank sender was a stable 0.86V. Driving a few miles to the gas station, the right tank sender fluctuated from 0.80V up to 1.02V. Based on the service manual, an empty tank should read between 0.4V and 1.0V. A half tank is around 1.5V. A full tank reads between 2.5V and 2.9V. Below 0.4V or above 2.9V is out of range and will throw codes P1432 or P0463.

I am surmising the times I observed the right tank reading over 1.0V may be the cause of the P1431 not thinking the right tank was truly empty. I intend to check the resistance of the right sender next time I get P1431 and see how much lower than 250 ohms it is. I may even attempt to clean the existing sender with Top engine cleaner and see how the resistance and voltage are affected before replacing it.

Lastly, I filled my tank and stopped at each gallon to snapshot the voltage from both sensors and percent-full reading. The voltage readings were quite stable, but the liters was a moving target and would slowly climb. Hope this information may help someone else troubleshooting fueling sender issues.

Gallons Added, Left Volts, Right Volts, Liters Left, Percent Full
0 1.94 0.86 26.8 38%
1 2.14 0.84 28.4 41%
2 2.45 0.84 34.9 50%
3 2.57 0.84 39.2 56%
4 2.57 1.02 41.5 59%
5 2.57 1.25 45.2 65%
6 2.57 1.37 48.2 69%
7 2.57 1.55 51 73%
8 2.57 1.71 54 77%
9 2.57 1.98 58 83%
10 2.57 2.22 62 89%
11 2.57 2.49 67 96%
12 2.57 2.51 68.7 98%
12.26 2.57 2.55 70 100%



Todd

 

Almost every tank this past year has thrown a P1431 code and sent the gas gauge to zero just after passing half-tank, so I was aggravated enough to tear into it today. I had already run the tank down to the last 2 gallons, then pulled the passenger side wheel well liner, fuel tank shield, and removed the sender for a good cleaning. The float arm removed pretty easily by removing a black plastic retainer. I used both a pencil eraser, then a light emery paper to remove the 18 years of buildup from the contact surface. The two electrical "pucks" on the float-arm side did not need much attention.

During the test drive after assembly, the passenger tank reading was a rock-solid 0.71V compared to the variations noted last year. Hopefully this 90 minutes of cleaning will solve the issue for a good many years.

If you're thinking about trying this, run the tank down pretty far, and jack the back end up high to prevent fuel leakage when removing the sender. An empty gas tank with fuel vapors can be more dangerous than a full one, so keep it ventilated.



Todd




Electrical contact points before cleaning

Electrical contact points after cleaning

 

Just to toss this in there. If it looks like this don't waste your time. After 8 bottles of techron i gave up. LOL

 

nice right ups

 

Did you take full and empty resistance readings of a good unit or do you know what they should be? Question applies to both left and right sides. Thanks,.