I have found limited information on fuel tank replacement process (I.e. tips, videos, etc) so I am contributing my experience. I am not trying to duplicate the Toyota technical manual which should be used for troubleshooting and repair instructions. What follows is diagnosis, fuel tank replacement, and a confirmed fix. Background: new to us 2006 Prius accepted 3.5-4 gallons of fuel when flashing empty on combination meter. Fuel gauge reproducibly dropped gradually to 1/2 full on the meter then suddenly went to empty at approximately 150 miles range. Diagnostics: back seat removed, butyl sealed cover over fuel tank electrical connections pealed off. Gray connector disconnected (only connector with one side integral to tank). I measured the resistance between pins 5 and 6 tank side and found approx 110 ohms on a full tank, and 240 ohms on empty. These readings are out of range for the fuel tank sending unit and implicate the fuel level sending unit (integral to tank) as a problem. I then followed troubleshooting for the combination meter and wiring. I started the car with the same gray connector disconnected (open circuit) and fuel gauge read empty. I shorted pins 5 & 6 in the combination meter side of the gray connector and the fuel gauge read full. These findings confirmed that the wiring integrity to the combination meter and the meter itself were working. Collectively, the fuel sending unit was bad and thus repair would require that the fuel tank assembly be replaced. (I did reset the inclinometer on a flat level surface but this was not technically indicated given symptoms) More about replacement in next post…. This YouTube video was helpful albeit brief:
Here is my experience: Toyota service manual instructs the removal of the exhaust distal to the manifold. I did not find removal of the exhaust necessary. The height of the fuel tank assembly is such that having the car on 4 standard jack stands provides room to replace the assembly. After the battery negative was disconnected, all electrical connectors at the previously mentioned fuel tank access from inside the car. All fuel and vent lines were disconnected. Read the Toyota manual for instructions for the mechanism of each plastic connector. There are 2 fuel lines in the front and three in the back of the fuel tank to be disconnected. Be prepared with a basin and absorbent pads for fuel spillage. Connectors were covered with small plastic bags for protection. All that is left is the filler neck and straps. The “C clip” around the fuel filler neck (found on rear left) was pulled off. The fuel tank filler neck and tank are rigid and can’t be simply pulled apart. This proved to be the most difficult part of removal and installation, although not terrible, A jack was placed under the tank assembly for support. The 4 bolts for the fuel tank assembly supporting straps were removed and the straps pulled down. Once the tank was freed from all connections except the filler neck, and lowered somewhat, the tank was manipulated to disconnect it from the filler neck. Some force was required and ultimately it was apparent that tank needs to slide off following the angle of the filler neck or it will seem stuck. Fuel tank lowered on jack, then to ground and slid out. more…
Although I did not need to remove the exhaust, there was some minor maneuvering of the tank required because of the exhaust. Once the tank was removed, all of the hoses/lines, electrical lines, and charcoal canister attached to the assembly needed to be transferred to the new fuel tank assembly. This process is intuitive but the technical manual has step by step instructions. I won’t detail each step of the transfer. The “new” insulation pads were already adherent to the OEM fuel tank assembly top surface. The manual recommends two new gaskets at two large tank orifices. I had trouble finding a part number in advance, but found the gaskets to be labelled 77179-33010. My gaskets were in good shape and I hadn’t preordered new gaskets so I reused the gaskets. After all lines, hoses, etc were transferred to the new fuel tank, the new tank was installed. The tank was lifted with a jack until close enough to the filler neck to slide the tank onto the filler neck. After tank fully was lifted in place, the straps were reattached with 4 bolts. The 5 fuel/vent connectors were reattached, battery reconnected. Fuel added and vehicle started. No codes were present and vehicle has functioned normally. Hope this will help someone in the future. Comments or ? welcome.
Well done, Redknife! For those who plan to tackle this in the future: One thing to keep in mind for this job is to get the tank as empty as possible prior to removal. Another important item is attention to detail. Recently worked on another members Gen 2 due to a repair shop doing poor quality work on a (improperly diagnosed, not required) fuel tank replacement. During removal, found brackets with fasteners not installed or tightened and hose clamps not put back into position, etc. Not to mention, they didn't even clean the replacement tank. I reinstalled the original fuel tank. Prior to starting work, take PHOTOS of everything from multiple angles. Take good photos of the filler neck and where it attaches. You'll probably need to reference them after you initially get your butt kicked trying to reconnect it. After tank removal, take photos! When you transfer the components from the old tank to the new tank, pay attention to where everything belongs and how it's routed. Photos photos photos!! They don't lie and they don't forget. The constant tension clamps will need to be slid up the hoses so you can disconnect. Do not forget to slide them back into 'clamp' position on the new replacement tank. Lubricate the seals on the replacement tank prior to assembly. Forgetting these small items can lead to future emissions related codes that would require dropping the tank again, and once is enough! Not a difficult job, just awkward for one person. Do it right the first time! Watch some you tube videos first. Most of them have a few things I would avoid, but they do provide a good starting point. When I drained the old tank after removal, I just stood the tank on its end above a funnel feeding a 5 gallon fuel can overnight. I also pulled the entire exhaust prior to the tank job. It does make it a bit easier not having to wiggle the tank around the exhaust piping, but as mentioned, not 100% required.
