Ha when did that happen?? Wonder what he moved into.
Auxiliary Fuel tank for the empty space under the LX600?
- Thread starter CyanideRide
- Start date
This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.
We are missing some weldments on the frame for the tank mounting straps; so I've started designing some hanger brackets that will bolt up as a substitute for the missing weldments. Aside from taking care of some other priorities, I'm also wanting for my sliders from Slee to arrive before I move forward. I want to make sure the fuel tank bracket won't conflict with the slider mounting.
In watching the video, towards the end as he’s lowering the vehicle, it looks like the spare tire might be lowered somewhat. Like it now hangs a bit lower.
Is that correct or am I just looking at it wrong?
The aux tank is, by far, my favorite mod on my LC, but I had to move the spare tire to a swing-out on my rear bumper - which is annoying in day-to-day use.
So I’m envious if you can have the extended range without drawbacks.
EscapeWagon62
SILVER Star
PROBLEM!
I’ll cross post this to the FK fuel tank.
Driving down the freeway today I got a check engine light “parking assist inop” warning message (which toyota seems to use as a default in many models)
Total luck - I was two exits away from my Lexus store and they agreed to let me roll in at 4:55pm
Bad luck - The fault is due to fuel level mismarch based on miles driven. Also of note…I have 326 miles since fillup, averaging 18.4 MPG and the gas gauge is still pegged above full (I should be well into the main tank at this point)
I’ll readh out to FK
Has anyone else already experienced this and knows of a solution.
Error readout and fuel/trip/gauge photos attached.
I’ll cross post this to the FK fuel tank.
Driving down the freeway today I got a check engine light “parking assist inop” warning message (which toyota seems to use as a default in many models)
Total luck - I was two exits away from my Lexus store and they agreed to let me roll in at 4:55pm
Bad luck - The fault is due to fuel level mismarch based on miles driven. Also of note…I have 326 miles since fillup, averaging 18.4 MPG and the gas gauge is still pegged above full (I should be well into the main tank at this point)
I’ll readh out to FK
Has anyone else already experienced this and knows of a solution.
Error readout and fuel/trip/gauge photos attached.
EscapeWagon62
SILVER Star
No solution but did receive a timely response.
I will follow up with my tech at Lexus.
I’m going to drive it some additional miles to see if my gas gauge starts coming down (which is more of a concern to me than check engine as of today)
FK Note back on my inquiry:
Yes, we have encountered this issue before.
Based on our analysis and real-world testing, the root cause is related to the auxiliary tank’s fuel transfer behavior. During driving, the auxiliary tank continuously supplies fuel to the main tank, which causes the fuel level in the main tank to remain nearly unchanged for an extended period of time.
This is exactly where the issue originates. From the LX600 ECU’s perspective, a stable fuel level despite ongoing fuel consumption is considered abnormal. After several driving and calculation cycles, the ECU may trigger a diagnostic trouble code such as P0460.
At this stage, we have observed that this phenomenon is specific to certain models, most notably the LX600 and GX550, after the installation of an auxiliary fuel tank.
In summary, the root cause is:
the fuel level float in the main tank remains within a very narrow movement range for a prolonged period, even though fuel is being consumed.
Our currently discussed solution option is:
Please feel free to let us know if there is anything we can assist with. We are happy to provide any available technical support or further clarification.
I will follow up with my tech at Lexus.
I’m going to drive it some additional miles to see if my gas gauge starts coming down (which is more of a concern to me than check engine as of today)
FK Note back on my inquiry:
Yes, we have encountered this issue before.
Based on our analysis and real-world testing, the root cause is related to the auxiliary tank’s fuel transfer behavior. During driving, the auxiliary tank continuously supplies fuel to the main tank, which causes the fuel level in the main tank to remain nearly unchanged for an extended period of time.
This is exactly where the issue originates. From the LX600 ECU’s perspective, a stable fuel level despite ongoing fuel consumption is considered abnormal. After several driving and calculation cycles, the ECU may trigger a diagnostic trouble code such as P0460.
At this stage, we have observed that this phenomenon is specific to certain models, most notably the LX600 and GX550, after the installation of an auxiliary fuel tank.
In summary, the root cause is:
the fuel level float in the main tank remains within a very narrow movement range for a prolonged period, even though fuel is being consumed.
Our currently discussed solution option is:
- Masking or disabling the P0460 diagnostic trouble code. This approach is sometimes used in China in similar scenarios. However, we would like to better understand whether this solution is compliant with U.S. regulations, or whether this method is used in practice by installers or off-road specialists in the U.S. market.
Please feel free to let us know if there is anything we can assist with. We are happy to provide any available technical support or further clarification.
EscapeWagon62
SILVER Star
Good idea. I’ll get with my technician and figure out any and all options and report back. I seem to remember that his day off is Thursday but I’ll swing by the dealership.
Everyone at the store wants this tank setup to work. Several are cruiser heads plus some of their other clients are looking for better range.
An alternative idea is to use a fuel signal integrator.
The OEM aux tank has a secondary fuel level sender unit which is direct fed to the ECU. In my investigation the wiring harness for the secondary fuel sender unit is not installed in the truck. The next step (whenever I get around to it) will be to check the ECU the signal goes back to for the same pin out as the international truck. In which case it may be as "simple" as running new wiring to the ECU.
An aftermarket fuel integrator module may be able to take both sender unit signals and appropriately scale and output a signal the USDM ECU will like. I've not gone very far with the aftermarket option research at this time.
The OEM aux tank has a secondary fuel level sender unit which is direct fed to the ECU. In my investigation the wiring harness for the secondary fuel sender unit is not installed in the truck. The next step (whenever I get around to it) will be to check the ECU the signal goes back to for the same pin out as the international truck. In which case it may be as "simple" as running new wiring to the ECU.
An aftermarket fuel integrator module may be able to take both sender unit signals and appropriately scale and output a signal the USDM ECU will like. I've not gone very far with the aftermarket option research at this time.
I'm assuming because the aux tank is only 30L, that it's being triggered by (a) instead of A?
EscapeWagon62
SILVER Star
Really intriguing idea!
I’ll keep testing this thing and we’ll see where it ends up.
I knew this would be somewhat of an adventure but confident I’ll figure out a livable solution.
It’s just too good having the extra range to go back to full stock.
EscapeWagon62
SILVER Star
Not sure
More to come over the coming days
I just read your account on the other thread. If you drove 265 miles since fill-up, you should definitely not be on full for the primary tank. Did you get their extended range primary as well, or just the aux addition?
EscapeWagon62
SILVER Star
Just Aux and that is what I’m watching now.
On my first full cycle I had gauge anxiety as it wasn’t dropping when I thought it should but I hadn’t set a trip/odo to track it.
This time I did zero out the trip and waiting to see if and at what mileage the gauge begins to drop.
He traded for a F250 for towing reasons if im correct..
EscapeWagon62
SILVER Star
Good news - Updates and info (I'll cross post to the FK offroad tank thread as well)
OK, here is what I'm seeing.
1. Gas gauge
4. How am I feeling overall?
OK, here is what I'm seeing.
1. Gas gauge
- It's working - we can chalk this up to "gauge anxiety" but I did learn more about how it's functioning
- The fuel sender unit in the main tank is from FK.
- It seems to be biased towards full (shows above full at max) which gives the impression that it's stuck on full when in fact it is not.
- My gauge stayed above full, then to full and started dropping at ~360 miles (at 18.2 MPG avg) and then started to come down as normal. I've had vehicles in the past that can be full biased or empty biased. Now that I know how this one operates I'm fine.
- It was cleared easily
- In the USA, Lexus dealerships are not given access to mute or suppress codes nor would it be legal for them to do it if they did have access
- I'll have to buy a $30 OBDII tool to clear a code if it comes back.
- According to my techs, it is LIKELY that the CELs will stop as these systems are smart and always learning. It should (not guaranteed) realize over time that the vehicle is functioning normally.
- As I mentioned in an earlier post, the gas gauge wobbled a bit when transitioning form the Aux tank to the main tank.
- My bet is that this wobble as it sucked the last gas from the AUX was what caused the system to flag it as this was right around the mileage I'd expect the Aux tank to be emptying.
4. How am I feeling overall?
- I'd do it all over again in a heartbeat.
- I'll get about 630 miles out of one fill up (maybe more with freeway only)
- Do I wish I didn't throw a CEL? Yes but for $30 I'm not too concerned.
- Now that I know the behavior of the gas gauge/sending unit I won't have gauge anxiety anymore
- FK's customer support response time and willingness to help address issues is solid.
- I may end up ordering an extra fuel sending unit from FK as it's the only significant operational item (the others being hoses and the physical tank) that are not OEM at this point. Having a spare may be in my future just in case
- There are folks on this forum plus my technicians who are thinking about ways to get combined tank level readings. I'll just watch and see if anything solid comes along.
EscapeWagon62
SILVER Star
Just a quick update.
I’ve cycled thought the aux tank to main tank transition three more times with no CEL appearing.
I bought a $30 OBDII tool which I have in my glove compartment just in case I need to clear a code.
I’ll keep track and report back if I notice any reappearance and under which specific circumstances it appears.
I’ve cycled thought the aux tank to main tank transition three more times with no CEL appearing.
I bought a $30 OBDII tool which I have in my glove compartment just in case I need to clear a code.
I’ll keep track and report back if I notice any reappearance and under which specific circumstances it appears.
Just installed the aux tank by myself as a DIY job. I found myself wishing for a block diagram to confirm hose locations since the video moves quickly through the certain parts of the hook up. a transmission jack and a lift would have made things way quicker and more comfortable. I took my time and it was about 8 hours of work. Mine shipped with a new design of the rear bracket that does not require removing the trailing arm nut.
Tools I wished I had:
Trans jack
Crows foot wrenches (metric)
a 12 mm wrench, pretty sure mine is on vacation with a 10mm socket somewhere
Tools I wished I had:
Trans jack
Crows foot wrenches (metric)
a 12 mm wrench, pretty sure mine is on vacation with a 10mm socket somewhere
EscapeWagon62
SILVER Star
Just a longer term update.
No further CEL lights since my January post. My hypothesis is that I had some moisture in the system, it had been parked for a couple of days with a high temp of 20F and a low of -1F on the day of incident. Possible that the float was stuck since I was at roughly 300 miles and still reading full.
After several cycles it seems to wobble from 8/8 full to 7/8ths full when I’ve gone through approx 12.5 gallons and seems to start coming down predictably from 7/8ths full at around 14.5 gallons.
From that point everything tracks as it did before the aux tank install.
Absolutely love this modification.
No further CEL lights since my January post. My hypothesis is that I had some moisture in the system, it had been parked for a couple of days with a high temp of 20F and a low of -1F on the day of incident. Possible that the float was stuck since I was at roughly 300 miles and still reading full.
After several cycles it seems to wobble from 8/8 full to 7/8ths full when I’ve gone through approx 12.5 gallons and seems to start coming down predictably from 7/8ths full at around 14.5 gallons.
From that point everything tracks as it did before the aux tank install.
Absolutely love this modification.