Fuel Gauge Problem

[John333]

Hi All

 

I stalled my 2009 Gen2 987 Cayman S a couple of days ago when I was turning and reversing up a small incline to turn the car around on a street.

Shortly after (20 yards down the toad) I noticed the fuel gauge was reading zero and the message to add fuel came up. I knew that the tank was around 3/4 full so there’s obviously a problem with my fuel gauge/sender circuit. 

Thinking the incline may have jammed the float I removed the sender checked the resistance when moving it (which was normal), then I put it back in. The wires feeding the sender are showing 5v between them.

i tried shorting our the two wires at the senders connector with the battery connected but the gauge never moved. The gauge looks to flicker 1mm every time the ignition is switched on but doesn’t rise.

i can’t find a circuit diagram for the sender and gauge in the workshop manual I have so am not sure what else is in the circuit. Can’t find any reference to a specific fuse feeding the circuit either. 

Is there anything else I should check (relay somewhere?) before I go to the effort of taking the dash to hits to get at the gauge.? If the supply voltage is 5v then it must be dropped from 12v somewhere.? 

 

 Anyone Ideas?

 

Cheers

John

 

[Mavrik]

Hmm... Found this on the forum... May help? 

 

 

 

[John333]

Hi

Many thanks for the link... Info on this topic is very limited across the web in terms of Caymans. Fault usually lies with the sender in most cars and gauges tend to be pretty robust. This was the reason I went to the effort of removing the sender anyway.

If I was getting some form of reading on the gauge then it would point to a faulty sender but i’ve got nothing on it and it’s not moved from zero. An open circuit (high resistance value at the sender) would cause this I suppose.

 

The reason I think the sender is okay in my instance is that it not only tested okay when out the tank (moved freely giving the 10 to 300 ohms or so, but once back in again it reads around 80ohms which seems to tie in with how much fuel is in the tank.

 

The normal way to test if it’s a sender or gauge is the issue is to short the two wires at the sender connector (as if there was a full tank or well 0 ohms) and this should make the gauge go to full. I’ve done this (with the battery connected) and the gauge doesn’t move.

 

I just don’t have any info on is between  the gauge and the sender (just wires.?) and whether there are any other connectors or components in the circuit. If I knew I could maybe check them out for a bad connection and open circuit etc.Maybe the stall vibrated something loose.?

 

An open circuit at the gauge would cause the same issue that I have but i’m puzzled by the gauge needle flicking a tiny little on start up. I suppose a bad connection may still do this?

 

is the back of the fuel gauge hard to get at?

Assume it means dismantling the dash? Another weekend job..

 

Would appreciate any other info you are aware of...

 

Many thanks for your support on this it’s really appreciated. Only had the Cayman since March and this is the first real problem i’ve had on it.

 

i’ll have to make more trips to the service station to fill up until I bottom out the problem.

 

Cheers

John

 

 

 

 

[Aaron]

The dial cluster is easy to remove.

 

Replicate the resistance using a resistor.  I wouldn't rely on grounding it.  I'm not sure if the analogue signal is passed directly to the cluster, or if it's passed through a digital interface of some sorts.

[John333]

Hi All

 

Many thanks for the info. I think I’ve sorted the problem and thought I’d give an update so it might help others in the future.

 

So basically I thought it was too much of a coincidence that it happened right after I’d been parked with engine running on a steep incline (nose down).

 

 Thought I’d check other websites focussing on 911’s as I assumed Porsche probably used similar or identical fuel gauge systems on other models.

 

i read an article saying that if you run a 911 fuel tank empty then the gauge system can’t reset unless the tank fuel level is over a certain amount. I now think that my float in the tank dropped low (even though I had just under 2/3 tank full of petrol and this confused the system as I say there for a minute or so waiting for a breakdown van getting past and this may have made the gauge read empty. As I didn’t have a full tank then it couldn’t recalibrate after I set off again.

 

Thats my thinking anyway. So yes you guessed it, I have just been to the petrol station to brim my tank with super unleaded and when I switched the engine on the gauge was showing just under half a tank.

 

20mins of driving and the gauge slowly crept up to now show a full tank.  Switched engine off then on again when I got home and it jumped straight to full again.  Sounds like it might be a rare thing to happen on Caymans..

 

Happy days. Am back in love my Cayman 😁

[Windymiller]

That’s great intel John, thanks for reporting back on your fix - a good one to know. 👍🏻