Sub tank fault on 04 TD42

[Phat Patroller]

Ok patrollers I have encountered a problem.....

went through rather large bog hole, and about 10 mins later down the track the sub tank gauge had dropped to empty, and the sub tank light is on solid. Confirming that the tank had not been punctured (filled it up at the next servo)

I have read the repair manual and have tried the "sub fuel tank diagnosis system" but have been unable to to get it in diagnosis mode to find problem.

Things I have checked in sub tank unit:

Pump sender unit has resistance (roughly 5 ohms)
Pins on both plugs have good earths

Anyone with some experience in this matter please come to my rescue!!!!!!!!!!!

[Yendor]

Remove the sender from the tank and see if the float has fallen off.

[Phat Patroller]

Ok I shall give that a go tomoz, have you had that happen before?

[Yendor]

Yeah it's happened a few times.

[MudRunnerTD]

Have you tried disconnecting the Earth lead? i have had the subtonic light come on a few times and have disconnected the earth for 30minutes and cleared the fault. The gauge has never dropped to empty though? How hard is it to remove the sender Rodney? Drop the tank first?

[Phat Patroller]

I have tried to clear the fault, it keeps coming back within 30 sec of starting vehicle.

Yh I thought it was a bit different to some of the other problems on here no one mentioned a sub gauge showing empty.

And I already have access to the sender from inside the truck under the rear right hand seat. I'll check out the float today hopefully if it has come off, the thing is easy to find in a full tank :-/

[Yendor]

Have you tried disconnecting the Earth lead? i have had the subtonic light come on a few times and have disconnected the earth for 30minutes and cleared the fault. The gauge has never dropped to empty though? How hard is it to remove the sender Rodney? Drop the tank first?

Hey mate,

The key to this problem is the fuel gauge not reading at all.

There's an inspection cover in the floor for the sub tank just behind the drivers seat. Just lift up the carpet remove the inspection cover and you have access to the sender unit in top of the fuel tank. You don't need to remove standard fuel tanks to access the senders.

[Yendor]

I have tried to clear the fault, it keeps coming back within 30 sec of starting vehicle.

Yh I thought it was a bit different to some of the other problems on here no one mentioned a sub gauge showing empty.

And I already have access to the sender from inside the truck under the rear right hand seat. I'll check out the float today hopefully if it has come off, the thing is easy to find in a full tank :-/

You will more then likely have to disconnect the battery to clear the code once you have fixed the problem.

[Phat Patroller]

Just checked the float, no problem there. I confirmed by raising and lowering float in tank and checking for varying resistance.

I tend to agree it's the gauge not reading, but it's not at the tank.

Any other ideas?

[Yendor]

Next step is to confirm continuity in the wire between the sender unit and fuel gauge.

Get under the rear of the vehicle and check the wire harness as it comes out near the back of the sub fuel tank and runs across the chassis cross brace, just in front of the rear diff. Look for any signs of damage to this harness.

With ignition on measure the voltage in the fuel sender wire at the sender unit (sender disconnected). Try touching that wire onto earth and see if the gauge moves.

edit: Don't use the earth wire in the harness. Test using the body.