Tech Tip: Subaru Fuel Gauge Inconsistency On Forester – UnderhoodService

Tech Tip: Subaru Fuel Gauge Inconsistency On Forester

The Subaru Techline has received calls about a customer concern that the vehicle's fuel gauge shows only 3/4-full immediately after filling the vehicle. There are some easy checks that can be performed that will save diagnostic time.

The first thing that should be done is to verify that the vehicle is full of fuel. Once confirmed, check the fuel level resistance reading using the Subaru Select Monitor III (SSMIII). (According to Subaru, the aftermarket version of the SSMIII, referred to as the ­Hitachi Diagnostic System [HDS], is available through Blue Streak Electronics [BSE]. The HDS tool provides the aftermarket with the exact same functionality as the SSMIII. For more information on the HDS, go to

The reading should be anywhere from 2 to 8 ohms. If the reading is higher, remove the rear seat bottom so that the sending units can be individually checked. The fuel gauge position is an output from the BIU (body integrated unit), which takes a combined resistance reading from the two sending units, then ­averages them to determine how much fuel is in the vehicle.

Once the rear seat bottom is removed, unplug both sending units so that resistance can be checked across each unit. With the vehicle full of fuel, each sending unit should have 1 to 4 ohms of resistance. While checking the resistance, tap lightly on the top of each sending unit. If the resistance reading fluctuates while tapping on it, closer inspection or replacement of the sending unit is necessary. Sending units do not need to be replaced in pairs. Replace only the sending unit that has failed.

While you have the sending units exposed, you should check the operation of the fuel gauge. On the sub-unit, install a jumper lead between the two pins of the harness connector when it’s unplugged from the sending unit. On the main unit, jump pins 1 to 4 of the harness connector (unplugged from the sending unit). Keep in mind that it may take up to 45 minutes for the gauge to read full depending on the fuel level in the tank.
Fig. 1
Also, be sure to check connector I-10 at the combination meter for any signs of poor contact. See Fig. 1.

Technical service bulletin courtesy of Mitchell 1.

For more information on Mitchell 1 products and services, automotive professionals can log onto the company’s website at

You May Also Like

How (And Why!) To Clean An Engine

Beauty is more than skin deep. Here are 11 steps to help clean any car’s engine compartment.

A well-kept car looks amazing when rolling down the street, and it drives better. But, more driving means exposing a car to pebbles, grime, greasy and oily residues, dirt and particles. This unwanted debris can also accumulate under a car’s hood.

For a car owner to enjoy the beauty of a clean car, it’s vital to address the cleanliness of the interior, exterior and under the hood — the engine.

Spark Plug Fouling

Understanding why spark plugs get dirty.

Aging Plastic Intake Components May Cause Leaks

BMW valve covers and intake manifolds made of plastic are susceptible to warpage and gasket failure.

Diagnosing Intercooler Boost Trouble Code P0299

The criteria for setting the code is very basic.

Understanding Coolants

All-season coolant used inorganic acid technology and worked great for almost 30 years.

Other Posts

Misfire Codes P0300, P0301-P0312 and P0313+P0314

The only way to clear the code is to use a crankshaft position relearn with a scan tool.

Belt-In-Oil Timing Systems

Oil contamination of the belt drive has been a death sentence, due to the rubber and fiber construction of the belt.

What Caused The Turbo To fail?

Up to 50% of turbocharger failures are due to oiling problems.

New Oil Specifications

Many 0W16 oils have a new donut certification mark on the bottle called API SN-PLUS and SN-PLUS Resource Conserving.