TECHNICAL INFORMATION TIP

Reference Number(s): SUB0317AP, Date of Issue: December 1998

MIL COMES ON AT HIGHER ELEVATIONS - NO-KNOCK KNOCK SENSOR TEST

MODEL(S): 1995-98 Subaru Impreza

1990-98 Subaru Legacy

1998 Subaru Forester

1988-91 Subaru XT6

DATE OF ISSUE: December 1998

ISSUE & TIP

My shop is located at a 5000-foot elevation, and I am starting to see MIL's on late model Subarus equipped with 2.z and 2.5 liter engines. As near as I can determine, this is caused by a problem with the ECM programming and is not due to an actual malfunction. I have talked with other shops at similar elevations and they are seeing the same thing.

The ECM apparently tests the knock sensor after startup, but after 60,000 miles or so the engine will no longer knock on command at higher elevations.

Because there is no return signal from the knock sensor following the test, the ECM thinks the knock sensor is defective.

If the MIL does not illuminate at lower elevations, there is no problem. Replacing the sensor will not make any difference. The MIL will still come on at higher elevations and you will have wasted the customer's money and your time. As far as I have been able to determine, there is no permanent fix for this problem at this time.

Courtesy of Import Service Magazine

with thanks to:

Dan Rickert

Almanor Import Repair

Clear Creek, California

REFERENCE NUMBER

SUB0317AP

NOTE: This information has been obtained from sources generally believed to be reliable. Use your own judgment before relying on this data. Neither the suppliers of these Technical Information Tips, nor lemon-25 Repair Information Company, LLC, guarantees or assumes responsibility for data accuracy or completeness, nor is liability assumed by the suppliers of these Technical Information Tips or lemon-25 Repair Information Company, LLC, for any claims or damages resulting from the use of this information.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Mil Illuminates At Higher Elevations - Knock Sensor (SUB0317AP)