Tech Tip: Subaru Fuel Gauge Inconsistency On Forester – UnderhoodService

Main Navigation

Advertisement
Social Connect
Resources
Our Brand Family
Underhood Service Logo
Technical resources to help diagnose and repair engine-related service issues.
Engine

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.

Underhood Service Staff Writers
By Underhood Service Staff Writers
Published:

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 www.bsecorp.com/hds.php.)

Related Articles

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 www.mitchell1.com.

You May Also Like

External Engine

Alternator Testing For No Charge Conditions

Many alternator problems turn out to be nothing more than a bad connection at the alternator or a bad wiring harness.

Andrew Markel
By Andrew Markel
Andrew Markel is the director of content for Underhood Service magazine. He has been with Babcox Media for 20 years. He is a technician and former service writer and holds several automotive certifications from ASE and ­aftermarket manufacturers.
Published:

If only battery voltage is present at the battery on a running engine, does this mean the alternator is “bad?” No, it does not. It only means that the alternator is not charging, but does not reveal why. Therefore, it does not point to a faulty alternator. All too often, the alternator is condemned by technicians due to this test alone. The cause could instead be a module that distributes the power to the vehicle and regulates the alternator.

Read Full Article

More Engine Posts
Understanding Coolants

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

By Andrew Markel
Ignition System Do’s and Don’ts

Why do ignition systems give technicians problems when diagnosing ignition-related misfires? The answer is that some technicians use tests that might give inconclusive results or do damage to the coil or drivers inside a module.

By Andrew Markel
Tools To Service Serpentine Belts

Servicing the serpentine belt on some vehicles is a tough task.

By Andrew Markel
Battery Charging and Diagnostics

Here are six tips to use when diagnosing a vehicle with a dead battery. 

By Andrew Markel

Other Posts

Why Do Timing Chains Stretch?

As the timing chain wears, it can change the timing of the camshaft and crankshaft.

By Andrew Markel
Carbon Deposits and Direct Injection Engines

The primary cause of these problems is that fuel and added detergents are not hitting the back of the intake valves.

By Underhood Service Staff Writers
Acura Turbo Engine Service

It is important to check the operation of the solenoids that control vacuum to the actuators.

By Andrew Markel
Subaru EJ25 Head Gasket Problems

Most of the EJ head gasket failures occur around the 100,000-mile mark and start as a slow oil or coolant leak.

By Andrew Markel