Changing Battery / Fuel Gauge

[dlipka]

Hi Folks,

I have just changed the battery in my car (99 C4) and now the fuel gauge has an error in it. Prior to changing the battery, the fuel gauge read at 1/4 full. With the new battery fitted, the gauge was on empty and warning light was illuminated. I went and filled the car up (I made absolutely sure that it was full) and the gauge now reads 3/4 full. Switching the car on / off makes no difference to the situation.

Any suggestions?

Thanks,

Derek

[topmech0]

Hi Folks,

I have just changed the battery in my car (99 C4) and now the fuel gauge has an error in it. Prior to changing the battery, the fuel gauge read at 1/4 full. With the new battery fitted, the gauge was on empty and warning light was illuminated. I went and filled the car up (I made absolutely sure that it was full) and the gauge now reads 3/4 full. Switching the car on / off makes no difference to the situation.

Any suggestions?

Thanks,

Derek

it sounds like you will have to take it to OPC or an indy with system 2 tester. the gauge will have to be recalibrated. its a strange sequence but in general tank must be completely drained and a measured amount(think its 28 litre) put in and gauge then calibrated with the porsche system 2 tester. oh and that figure is european,not US litres. yours are about 0.9 of ours!!

[PAULSPEED]

Hi,

I would fill the car up, then disconnect the battery

for five minutes, and then connect the battery.

Good luck.

Paul

[Loren]

topmech0 is correct.

If you disconnect the battery on a C4, C4S or TT with under 1/4 tank - you will need to get the tank re-calibrated using a PST2 or PIWIS.

Those cars use a "saddle bag" gas tank and the sensor is only on one side. So one side of the tank is "estimated" on the fuel gauge - based on the a specific amount of fuel in the tank at calibration time.

If you lose that calibration setting by disconnecting the battery (with a low tank) the tank/cluster has no guess as to remaining fuel and MUST be re-calibrated.

As I recall there is a warning about this in the Owners Manual.

[dlipka]

topmech0 is correct.

If you disconnect the battery on a C4, C4S or TT with under 1/4 tank - you will need to get the tank re-calibrated using a PST2 or PIWIS.

Those cars use a "saddle bag" gas tank and the sensor is only on one side. So one side of the tank is "estimated" on the fuel gauge - based on the a specific amount of fuel in the tank at calibration time.

If you lose that calibration setting by disconnecting the battery (with a low tank) the tank/cluster has no guess as to remaining fuel and MUST be re-calibrated.

As I recall there is a warning about this in the Owners Manual.

Hi - Thanks for all the advice - for the record I have just checked the owners manual - there is no reference to the fuel tank with respect to changing the battery....

Can I fix this myself?

Derek

[Loren]

You are correct the warning did not make it in the MY99 Owners Manual - I think it was added in MY01.

This is not a DIY unless you own a PST2 or PIWIS.

You have to empty the gas tank. Refill it with an exact amount of fuel.

Then the PST2 (or PIWIS) recalibrates the sensor and puts the calibration number in your instrument cluster.

[Last Car]

topmech0 is correct.

If you disconnect the battery on a C4, C4S or TT with under 1/4 tank - you will need to get the tank re-calibrated using a PST2 or PIWIS.

Those cars use a "saddle bag" gas tank and the sensor is only on one side. So one side of the tank is "estimated" on the fuel gauge - based on the a specific amount of fuel in the tank at calibration time.

If you lose that calibration setting by disconnecting the battery (with a low tank) the tank/cluster has no guess as to remaining fuel and MUST be re-calibrated.

As I recall there is a warning about this in the Owners Manual.

Hi Loren,

If I'm reading this right, a basic 1999 C2 will not have this problem, if the battery is disconnected; or should I make sure the tank is full anytime I disconnect the battery?

thanks,

[Loren]

topmech0 is correct.

If you disconnect the battery on a C4, C4S or TT with under 1/4 tank - you will need to get the tank re-calibrated using a PST2 or PIWIS.

Those cars use a "saddle bag" gas tank and the sensor is only on one side. So one side of the tank is "estimated" on the fuel gauge - based on the a specific amount of fuel in the tank at calibration time.

If you lose that calibration setting by disconnecting the battery (with a low tank) the tank/cluster has no guess as to remaining fuel and MUST be re-calibrated.

As I recall there is a warning about this in the Owners Manual.

Hi Loren,

If I'm reading this right, a basic 1999 C2 will not have this problem, if the battery is disconnected; or should I make sure the tank is full anytime I disconnect the battery?

thanks,

Correct it is only 4WD cars where Porsche used the "saddle bag" gas tank. Those would include C4, C4S, and TT.

[Last Car]

topmech0 is correct.

If you disconnect the battery on a C4, C4S or TT with under 1/4 tank - you will need to get the tank re-calibrated using a PST2 or PIWIS.

Those cars use a "saddle bag" gas tank and the sensor is only on one side. So one side of the tank is "estimated" on the fuel gauge - based on the a specific amount of fuel in the tank at calibration time.

If you lose that calibration setting by disconnecting the battery (with a low tank) the tank/cluster has no guess as to remaining fuel and MUST be re-calibrated.

As I recall there is a warning about this in the Owners Manual.

Hi Loren,

If I'm reading this right, a basic 1999 C2 will not have this problem, if the battery is disconnected; or should I make sure the tank is full anytime I disconnect the battery?

thanks,

Correct it is only 4WD cars where Porsche used the "saddle bag" gas tank. Those would include C4, C4S, and TT.

Thanks you Sir.

[AgeRebel]

Is this issue and warning applicable to subsequent MY's too? I have an 04 C4S and did not see any warning in the User's Manual. Was wondering and hoping that Porsche/Audi improved on this somewhere along the way.

[Loren]

Have a look at TSB 9/99 2015 Carrera 4 – Running Out of Fuel -- dated 10-14-99

"To summarize, if the battery is disconnected with the fuel level less than 1/4 tank, the fuel level and driving range on remaining fuel values will be incorrect. When the battery is reconnected, the fuel calculation will default to 19 liters, when in fact, the fuel level is most likely less than 19 liters. This can result in the vehicle running out of fuel, with a seemingly good fuel level indication."

[AgeRebel]

Have a look at TSB 9/99 2015 Carrera 4 – Running Out of Fuel -- dated 10-14-99

"To summarize, if the battery is disconnected with the fuel level less than 1/4 tank, the fuel level and driving range on remaining fuel values will be incorrect. When the battery is reconnected, the fuel calculation will default to 19 liters, when in fact, the fuel level is most likely less than 19 liters. This can result in the vehicle running out of fuel, with a seemingly good fuel level indication."

Thanks Loren! I found it in my owner's manual ('04 C4S), in a different section and it says;

"If the remaining fuel is less than approx. 1/3 of the overall tank capacity while the battery is discharged or disconnected, incorrect information will be displayed when the battery is charged or reconnected.

The fuel level gauge may indicate more fuel than is actually in the tank.

The range on remaining fuel displayed by the onboard computer may be higher than in reality.

In this case, in order to ensure that gauges are precise and that you do not run out of fuel, you should fill up your car with fuel."

Firstly, I found the last sentence very amusing :D

So it looks like there were some changes since the TSB. However, its still unclear to me if the tank needs to be re-calibrated. The way I read it, it self recovers once you fill up the car. Be nice to know so we don't inadvertently run dry!