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P0183 & Replacement of Fuel Temp Sensor in 2004 Sonata.
A garage I thought I could trust charged $200 to read the check engine light and determine the FTS was out of spec. They wanted another $800 to replace the fuel pump assembly which they said included the non-separable FTS. I said no to the replacement and got the $200 bill down to $120 and left. I was surprised, but pleased, that the check engine light was out so I assumed that fiddling with the wire harness/connector caused the light to go out. During the 2 weeks or so the light was on, there was no noticeable change in engine operation or gas mileage.

Six months later the check engine light came on again. I bought a code checker for $95 and got the same P0183 code. With Google and the Hyundai forums I found out the FTS was a separate component that could be replaced once the fuel pump was removed from the fuel tank. The FTS (hyundai part no 31435-38300) cost $34.58 plus $9.99 shipping and was bought from Courtesy Hyundai (www.courtesyri.com) on the internet.

I have a 4-door sedan and the fuel pump assembly is easily accessible. Open the rear passenger-side door, lower the seatback, lift the black trunk floor covering and there is a plastic access plate with a wire harness passing through its center. Lift the access plate, mine has a black stickum holding it to the white trunk bottom surface. You’re now looking at the mounting plate of the fuel pump assembly which attaches to the top of the fuel tank. (see attachment)

You will see 2 hose connections: a high pressure hose held in place by a hex-head metal bolt and a return line held in place by a squeeze clamp. There are 2 electrical connectors: a white one with 5 pins that supplies power to the pump and a black 2 pin connector that attaches to 2 screws that pass through the mounting plate. The FTS has long leads which attach to the underside of these 2 screws. Both electrical connectors are easily separated by pressing a small tab near the midline.

At this point I had dropped the rear seat back, moved the trunk floor covering, lifted the plastic access plate and disconnected the black connector. This reveals two metal prongs on the half of the connector still connected to the pump mounting plate. I connected an ohm-meter to each prong and got an open (infinite) reading. This meant I had to remove the fuel pump assembly because even if FTS was okay and one of the leads that connect to the underside of the mounting plate had come undone I still had to remove the pump assembly to reconnect the lead. I ordered the FTS but didn’t open the packaging until I confirmed the leads were connected properly and the FTS was bad.

Following shop manual instructions I depressurized the fuel system by disconnecting the white 5-prong connector, removing the gas cap, attempting to start the engine (it will stall) for 3-4 seconds, then turning the key to off. Next, I disconnected the negative battery cable, then disconnected those two hoses on top on the mounting plate. The high pressure hose held in place by the mounting bolt lifts straight up. At this point you need to have packed some paper towels under the hoses because some gas will spill. Next, I removed the six phillips head screws holding the mounting plate to the top of the fuel tank. I was concerned about the gasket that sits between the bottom of the mounting plate and the top of the fuel tank. The local Hyundai parts manager was very helpful, e.g. he called the gasket a packing ring, but couldn’t recall ever ordering one which meant that the mechanics reuse the original packing ring.
Now come the crux moves. If anyone with more experience (I’ve done this exactly once) or knowledge wants to refine the next paragraph please do.
With the six mounting screws removed I broke the seal which had formed between the mounting plate and the gasket by lifting on one side of the plate then the other then both sides. It took a minute or so of careful pressure and then the mounting plate came free. The gasket looked new. Before the next step I made a mark on the trunk flooring to match up with a tape label ( EF + in the picture) attached to the mounting plate so I’d replace the assembly in the correct orientation. The float level and filter require you to tilt the pump assembly when lifting so neither is damaged. I was having a difficult time until I raised the mounting plate an inch or three from its resting position, rotated it about 90 degrees CCW, and tilted the top away from me and out of the tank. During this quasi-obstetrical procedure I was kneeling on the rear passenger seat with my arm resting on the lowered seat back.

With the assembly out of the car I looked into the tank and it seemed like the float sits in a small enclosure within the fuel tank and that first 2-3 inch lift is necessary for it to clear the enclosure wall and the 90 degree ccw turn is needed to allow you to tilt the assembly. I found the FTS right where it should have been near the bottom of the assembly and the long wire leads were solidly connected to the underside of the mounting plate. I connected the ohmmeter to each lead and the resistance was still infinite meaning the FTS was open and no good. I undid the new FTS packaging, and the resistance measured about 2K ohms.

I replaced the FTS, reconnected the leads, reinserted the assembly into the fuel tank, screwed down the mounting plate, connected the hoses and connectors, replaced the fuel cap, reattached the negative battery cable, turned the key, and the motor started. Start to finish the repair was about an hour. Best of all, that damned irritating check engine light isn’t on.

After word - I typically don’t do more than clean the car, change the oil and air filters, top off liquids, replace bulbs, and add air to the tires. In short I am not a mechanic so if I can do it so can you. If nothing else I ‘saved’ hundred of dollars and got the satisfaction of doing it myself, with the help of the hmauser.com website and forums.

My reading leads me to believe that P0183 is not a cause for immediate concern. The fuel consumption may be affected but I really didn't notice any change in gas mileage.

Following the safety precautions I put the car on the driveway, had all the windows down and the trunk lid open. I had lots of rags/paper towels at the ready in case of a gas spill and a fire extinguisher within arms reach the entire time. But I’ve spilled a lot more gas just filling the lawn mower.
There weren’t a lot of tools needed. Phillips head screwdriver, pliers for the squeeze clamp, socket/crescent wrench for the bolt holding the high pressure hose in place, needle nose pliers for fastening the tiny nuts that hold the FTS leads in place on the underside of the mounting plate, ohmmeter, and flashlight.