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Discussion Starter · #1 ·

New to the forum and I hope someone has an idea to help me. The wife's 2004 SLK 230'S fuel gauge is acting up, in that it won't read below 1/4 tank. I have removed the tank sending unit and using an ohmmeter moved the float from one extreme to the other. There are no dead spots, the resistance changes smoothly as I move the float. Even with the sender out of the tank but connected to the car, with the float at full empty, the gauge only goes to 1/4. When the ignition is OFF the gauge drops to the pin where it normally is.

Using a code reader in the OBD2 port I get a code of B1470, Googling the code shows that means the fuel sending unit is OPEN. But it's clearly not open as proven by the ohmmeter test.

A new sending unit is $400 and I don't want to part with the money unless it's a guaranteed fix, which I doubt.

I also never checked the total resistance of the sending unit's resistance coil. Is that information available somewhere?
I am thinking that if the total resistance of the unit is too low, the ECU may read it as OPEN even though it's not.

Right now we drive the car pretending that the 1/4 mark is EMPTY and we fill it from there... yes.. the gauge moves above the 1/4 mark on it's way to FULL.

Thoughts anyone?

Thank you in advance,


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2005 SLK55 AMG /2005 SLK350
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So you have the sensor out? What is the measured range of the varistor in ohms?

When it's installed, is it sending the minimum value?

On 171's at least, there are STAR tests to diagnose the stepper motor that moves the needle. I don't know about 170's.

The level sensor is wired directly to the Instrument Cluster with no intervening connectors (so no usual suspects are available for introducing corrosion/resistance).

IIRC there is a float involved with this sensor, any chance it's binding?
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