subaru legacy check engine light

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					     insider info.
Rough Idle On MPFI Vehicles
  If you encounter a rough idle
                                       plete before it can be inspected
                                       for proper emissions.
                                                                              23 consists simply of one wire
                                                                              from the ECM to the TCM. How-
complaint on any sequential              Misfire, Fuel System and Com-        ever, since this is a 1995 Manual,
injection MPFI vehicle, basic          ponent Monitoring are continu-         the pin terminal connection for
checks should be made to ensure        ously checked and will change          the ECM referred to in the diag-
that the correct injector wire con-    from Incomplete to Complete            nostic flow charts is B84, pin 33,
nector is on the correct injector.     while the ignition is turned from      which is correct for only the gray
Injector wiring will either be         off to on.                             connector of a 1995 ECM, not the
numbered or can be checked by            The Readiness Codes will all         blue connector on the 1996 vehi-
comparing wire colors with the         indicate incomplete after the mem-     cle you are working on. Referring
wiring diagrams. This may seem         ory of an ECM has been cleared.        to the engine control module
like an obvious check, but some-         Follow the steps below to acti-      (ECM) I/O (input/output) chart
times in your zeal to quickly diag-    vate the Readiness Codes to            (Sec. 2-7, page 68-70) in the 1996
nose a vehicle, the obvious can be     complete:                              Legacy service manual Supple-
overlooked. If two injector con-       • 1996 models: Connect the Test        ment, we find that the correct pin
nectors have been inadvertently        Mode (inspection mode connec-          location for the engine speed sig-
switched, the symptoms can be a        tor) and drive on a flat road (high-   nal for a 1996 blue connector is
slightly rough or irregular idle on    way) at approximately 50 to 55         B84, pin terminal 64.
a fully warmed up engine and a         mph for 20 to 30 minutes.                Without taking the extra step of
hesitation coming off the line.        • 1997 and later: Drive on flat road   looking in the 1996 Manual, the
                                       (highway) at approximately 50 to 55    wrong wire would be checked at
Reading OBD Readiness Codes            mph for 30 minutes for warm-up.        the ECM and the wrong diagnos-
  Many states are now including        Then perform 10 minutes at steady      tic conclusion would be reached.
an inspection of the OBD system        speed (without any throttle angle      To minimize the possibility for
as part of their emissions test pro-   change) at 50-60 mph.                  error, always double check the
cedure. This includes, but may                                                connector colors before attempt-
not be limited to, inspection of       Blue Versus Gray Connectors            ing to locate the pertinent pins.
the MIL or Check Engine Light for      During Diagnosis
proper illumination, operation,          When performing electrical diag-     Legacy (Non Turbo), SVX
and status of the Readiness            nostics involving the fuel injection   and Impreza ISC Valves
Codes.                                 ECM on 1995 through 1997 Legacy          If you encounter a vehicle with a
  Readiness Codes can be               and Impreza vehicles, pay particu-     driveability complaint (stalling, idle
checked with a generic scan tool       lar attention to the color of the      surge or a whistle noise) and you
and the New Select Monitor             connector that mates to the engine     have determined that it is caused by
(NSM). Follow the tree below to        control module. Some will be gray      the ISC valve, this condition may be
access the Readiness Codes with        and some will be blue. The con-        due to carbon buildup inside the
the New Select Monitor:                nectors are not the same and the       valve. In these cases, use the ISC
• Each System Check                    pin terminal locations that corre-     cleaning procedures found in the
• EGI                                  spond to the related systems in the    1995 Legacy service manual, Book
• OBD System                           car are different.                     1, Section 2-7. Use Subaru Top
• 12 Data Display                        An example of where this could       Engine Cleaner (SOA868V9160).
  Any item that is a Readiness         cause confusion would be diag-         Products such as Brake Clean do not
Code will have an indicator to the     nosing a TCM Code 23 (engine           effectively remove the deposits.
right that tells you whether it is     speed signal) on a 1996 Legacy           White exhaust smoke during ISC
Complete or Incomplete. Com-           vehicle. Looking in the 1996 Sup-      valve cleaning is normal. An odor
plete means that the system has        plement Manual, you’ll find that       also may linger for a few days.
been tested by the onboard diag-       there is no Troubleshooting Sec-         These valves are pre-set. Never
nostic system. Incomplete means        tion 3-2. This means the transmis-     try to adjust them in an attempt
that the system has not been test-     sion control system has not            to repair a vehicle. If you find
ed. In either case the results of      changed since 1995 and is, there-      yourself working on a driveability
the test are not indicated. No sup-    fore, not included in the Supple-      concern, and this valve shows
port indicates that this vehicle is    ment. Opening the 1995 service         signs of tampering, the valve
not equipped with that system.         manual, you will see that in Trou-     must be replaced. There are no
  A vehicle must have all of the       bleshooting Section 3-2, the cir-      procedures to return them to the
Readiness Codes reading Com-           cuit pertaining to Trouble Code        factory settings.

                 insider info.
             Impreza Throttle Position Switch
                                                         sion is premature. Instead, you should
                                                         replace the idle air control solenoid,
               When checking voltages for the            clear the memory and test drive the
             Impreza throttle position switch, the       vehicle. Confirm proper operation of
             engine must be at operating tempera-        the air control valve and see that no
             ture and normal warm idle speed. If         Check Engine Light occurs. If the Check
             not, the readings you get will be incor-    Engine Light illuminates again with
             rect and you may make an adjustment         DTC P0505, perform all the other
             that is not necessary.                      checks for the code as detailed in the
               The throttle opener system which pro-     service manuals. If the checks are good
             vides cold fast idle, mechanically opens    but the code still occurs, only then
             the throttle valve and will cause your      should the ECM be replaced.
             throttle position sensor readings to          Remember: This only pertains to situ-
             change. The Impreza service manual          ations where the resistance of the idle
             instructs you to be certain the engine is   air control valve has been measured to
             at normal operating temperature when        be 5 ohms or less.
             making this adjustment. Changes when
             cold can affect driveability and vehicle    2.2 Liter Impreza Fuel Senders
             emissions during cold engine operation.       2.2 liter AWD Impreza vehicles have a
                                                         dual fuel sending unit configuration simi-
             DTC P0507 - Idle Control                    lar to the system that has been used on
             System RPM                                  Legacy vehicles. There are main and sub-
             Higher Than Expected                        senders that operate the fuel gauge. The
                                                         senders are wired in series, just like the
               If you find yourself diagnosing a DTC     Legacy.
             P0507 — Idle Control System RPM               The sub-sender is listed in the parts
             higher than expected — check to see if      books but not shown in the illustrations.
             the accelerator or cruise control cables
             are adjusted properly.                      Understanding P0440
                                                           In order to understand Code P0440,
                                                         Evaporative Emissions Control System
                                                         Malfunction (EVAP), we must first
                                                         understand that it is a performance
                                                         code rather than an electrical circuit
                                                         code. What this means is that to pro-
                                                         duce this code, the computer is not
                                                         looking for any improper resistances,
                                                         electrical opens, shorts, or sensor out of
                                                         range situations. Rather, it uses infor-
                                                         mation from various sensors to draw
                                                         conclusions about the proper or
                                                         improper physical operation of the
             DTC P0505                                   Evaporative Fuel Emission System.
               When following the diagnostic flow        Any electrical failures have different
             chart in the service manuals for DTC        failure codes associated with them.
             P0505, where the resistance of the idle       The job of the Evaporative Fuel Emis-
             air control valve has been measured to      sions System is to prevent evaporating
             be 5 ohms or less, make the following       fuel vapors from entering the atmos-
             revision to step #3 “Check Idle Air         phere and contributing to air pollution.
             Control Solenoid Valve.” After check-       In order to keep this from happening,
             ing the resistance of the Idle Control      the entire fuel system needs to be able
             Solenoid valve for “5 ohms or less,” if     to be sealed from any access to the out-
End Wrench

             the answer is “yes,” the service manual     side air. Vapors in the system are
             tells you to “Replace idle air control      trapped in a charcoal canister, and
             solenoid valve and ECM.” This conclu-       those vapors are later purged into the

intake manifold to be burned dur-       ister) and a line that goes to the      the tank is warmer than the fuel
ing the next driving cycle.             front of the vehicle, where it is       in the tank. This returning warm
   Only vehicles with the               attached to the electrically con-       fuel mixes with the tank fuel
Enhanced Evaporative Emissions          trolled purge control valve (pas-       and gradually warms it up. As
system can produce Code P0400.          senger’s side of the engine com-        the fuel in the tank warms, its
To identify which vehicles have         partment). Within the fuel tank,        rate of evaporation increases.
the enhanced system and which           there are fuel level sensors (the       Because the tank and system are
do not, look for the location of the    same ones that are used for the         sealed, the pressure in the fuel
charcoal canister. If it is small and   dash gauge) and a fuel temperature      tank increases.
under the hood, the vehicle does        sensor (attached to the passenger’s       The control unit looks for this
not have the enhanced system. If        side fuel sender). Tapped into the      pressure rise to determine if the
the canister is not under the hood      fuel filler neck air bypass pipe is a   system is sealed. If the desired
but is large and under the right        fuel tank pressure sensor (inside       pressure is achieved, the comput-
rear of the vehicle, the vehicle has    the trunk of a sedan or the luggage     er will continue on to the next
the enhanced system.                    area of a wagon).                       part of the test. In this part, the
   In the enhanced system, evapo-         To test the integrity of the sys-     control unit will close the canis-
rative vapors leave the fuel tank       tem, the system shuts off all           ter vent valve, open the tank pres-
and pass through lines to an elec-      access of the tank to the outside       sure control valve, and open the
trically controlled pressure con-       atmosphere. When the engine is          canister purge valve. This should
trol valve and a mechanical             running, gasoline is being deliv-       draw a low pressure on the tank.
rollover valve (both by the pas-        ered to the injectors and the             The computer monitors the fuel
senger’s side front of the fuel         excess unused fuel is returned to       tank pressure sensor to determine
tank) heading to the canister. The      the tank. Since the injector rails      whether the low pressure is
canister has an electrically con-       are hot due to their proximity to       achieved. If it is, it then proceeds
trolled vent valve (next to the can-    the engine, the fuel returning to       to the next part of the test. In this
                                                                                                    Continued on page 24.
                 insider info.
             part, it repeats the first part of the test
             to watch the pressure rise in the tank.
                                                           valve, apply a hand vacuum pump to
                                                           the valve and cycle the valve with the
               After the pressure rises, the control       Select Monitor in the compulsory valve
             unit does some math comparing the             operation mode while confirming that
             initial high pressure and the difference      the valve actually opens, fully closes
             between the low pressure and the final        and fully seals.
             high pressure. If the values fall within
             a specified range, the test passes. If the    Note: The tank pressure control valve
             values are outside the specified range,       and the canister purge control valve
             the test fails. After two consecutive fail-   should open when energized,. but the
             ures, the Check Engine Light is illumi-       canister vent valve is a normally open
             nated.                                        valve so it should close when energized.
               The testing of this system is only
             conducted once per drive cycle and              If the valves work properly, try pres-
             only under very specific conditions:          surizing the fuel tank (engine off) and
             • The fuel tank must contain less than 9.6    evaporative system with air to check
             gallons of fuel.                              for leaks. Do not exceed 3 psi when
             • The fuel temperature must be less than      pressurizing the tank or major fuel tank
             113°F.                                        damage can occur. You can pressurize
             • Engine speed must be over 1500 RPM.         the system through the fuel return line
             • Vehicle speed over 28 MPH.                  or with a modified gas cap with hose
             • Throttle position must be mid-range.        attached. Close or block off the canister
             • Intake manifold vacuum must be              vent solenoid to seal the system.
             equivalent to cruising vacuum.                  Another situation can exist if you do
             • 455 seconds must have elapsed since         see a pressure rise on the Select Moni-
             engine start.                                 tor while conducting the first part of
               The vast majority of P0400 codes            the tests when running the engine. In
             occur due to gas caps that have been          this case, you may have a situation
             left loose or the gas cap retaining tether    where the pressure won’t go high
             has become caught under the cap dur-          enough (due to a very small leak or a
             ing tightening. With the cap loose, no        poorly seating valve) or the pressure
             pressure rises or falls in the tank, so the   won’t go low enough (due to insuffi-
             test fails. If a loose cap can be positive-   cient purging vacuum). A vacuum of -
             ly eliminated as the cause of the code,       1.338 kpa in the tank is required to sat-
             follow the diagnostics in the service         isfy the test. A functional valve test and
             manual. If the diagnostics don’t lead to      a check of the supply of purging vacu-
             a definitive failure, there are a few         um would be required.
             other steps that can be taken.                  Remember, because a precise set of
               The Select Monitor has a screen that        parameters must be met before the test
             displays fuel tank pressure. After starting   is conducted and two trips are required
             the vehicle, you should see a gradual         to turn on the Check Engine Light, a
             pressure rise in the tank due to the          considerable number of days can pass
             warming of the fuel. If you open the cap,     after a gas cap is left loose before a
             the pressure should drop immediately.         Check Engine Light may come on. This
               If you don’t see a pressure rise, there     may convince a customer that the light
             must be a vapor leak to the outside.          could not possibly be due to their leav-
             Closely inspect all lines and hoses.          ing the cap loose. Nevertheless, it may
             Physically check the operation of the         well be, and most likely is, the cause.
             pressure control valve solenoid, the
             purge control valve solenoid and the          Enhanced Evaporative
             canister vent valve. The service manual       Emissions Test
             instructs you to listen to these valves to      When the car is first started and you
End Wrench

             click, but that does not necessarily          begin to drive, the Pressure Control
             mean they are closing completely.             Solenoid comes on a few seconds later.
               Disconnect the hoses from each              The computer is looking for some pres-

sure change in the fuel tank to         see the Pressure Control Solenoid        the vehicle is judged to be okay.
indicate that the system has been       and the Vent Solenoid come on at
sealed and can be purged.               the same time. When the Pressure         More P0440 Information
  If the computer sees a change in      Control Solenoid comes on, the             With the introduction of the
the pressure, after about 40 sec-       computer is looking for a pressure       New Select Monitor (NSM), late
onds the Pressure Control Sole-         change in the tank. If it sees one,      model 1997 and newer vehicles
noid will turn off, and the vehicle     part two of the test has passed.         with Enhanced Evaporative Sys-
will have passed the first part of        The Vent Solenoid then comes           tems can be diagnosed more easi-
the test for the Enhanced Evapo-        on to shut off the vent to the out-      ly for DTC P0440. The NSM can
rative Emission System.                 side air. Since the Canister Purge       be set up to monitor the Pressure
  If the computer doesn't see any       Valve is also open at this time, the     Control Solenoid with one LED
pressure change, the Pressure Con-      entire evaporative system is             and the Vent Solenoid with
trol Solenoid will remain on for        drawn down to a low pressure: If         another LED while simultaneous-
the remainder of the drive cycle.       the pressure in the tank can be          ly reading the fuel tank pressure.
  If the first part of the test pass-   lowered to below -1.338kpa, part         With this setup, there is no neces-
es, the computer will wait until        three of the test has passed and         sity for the rapid button juggling
you are driving in a cruising con-      the Vent Solenoid shuts off, open-       that was necessary with the old
dition to perform the next three        ing the vent to the outside air.         Select Monitor to catch the chang-
steps of the test. If the vehicle is      The low pressure in the tank           ing pressures in the tank during
cruising over 45 mph but under          should begin to recover toward           the diagnostic phases of P0440.
80mph and has less than a half of       atmospheric pressure. If the pres-       After the system does its tests,
a tank of fuel, the next part of the    sure rise in the tank is sufficient to   save the data. You can then graph
test will begin.                        satisfy the fault code formula, part     the information on the screen.
  This second part of the test is       four of the test has passed, the Pres-     LED 6 (on the old Select Moni-
the only time when you will ever        sure Control Solenoid shuts off and      tor) corresponds to the Vent
                                                                                                             Continued on page 30.

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                 insider info.
             Solenoid (on the new Select Monitor),
             and LED 8 (on the old Select Monitor)
                                                      Continued from page 25.

                                                                Another unusual computer response
                                                              is if the computer is deprived of its
             corresponds to the PCV (Pressure                 “back up power supply.” If deprived of
             Control Valve) solenoid (on the new              this power, some computers will gener-
             Select Monitor).                                 ate a false code for the Idle Air Control
                                                              valve and kill the injector for cylinder
             OBD II Cylinder Misfire Codes                    #1. The pin location of this power sup-
                If you encounter cylinder misfire             ply can be found in the Control Unit
             codes on Subaru vehicles equipped                Module I/O Signal pages of the appro-
             with the OBD II system, check the past           priate service manual.
             service history to see if the vehicle’s
             fuel filter was recently changed.                1995 Subaru Legacy - DTC P0505 -
                There is a short period of time when          Idle Control System Malfunction
             the vehicle is first started, after the fil-       If you encounter a 1995 Subaru
             ter has been changed, when the cylin-            Legacy with a DTC P0505 (Idle Con-
             ders may not get the fuel charge they            trol System Malfunction), check to
             should. This may translate into a slight         see that the wire pins in connector
             cylinders misfire, which is enough to            B22 are securely fastened in the con-
             trigger a misfire DTC.                           nector. If pin 13 (BY) has backed out
                                                              of the connector, you will lose two
                                                              grounds at the ECU.

                                                              Diagnostic Trouble Code P1507
                                                                If you are diagnosing a manual trans-
                                                              mission-equipped vehicle with a DTC
                                                              P1507 and can find nothing wrong after
                                                              following the trouble tree in the appropri-
                                                              ate service manual, inspect the Neutral
                                                              Switch Circuit before replacing any parts.
                                                              The Neutral Switch Circuit may cause
                                                              this code to set. This could falsely indi-
                                                              cate to the ECU that the transmission is
                                                              in neutral when, in fact, it is actually in
                                                              gear. This can cause the MIL to illumi-
                                                              nate and set Code P1507.
               If the fuel filter was changed recently,         Keep in mind that the problem can
             clear the codes and test drive the vehi-         be intermittent and it may be necessary
             cle. Chances are good that the codes             to pin test the connection and to shift
             will not return if the filter change was         into and out of neutral many times
             the cause of the problem.                        before the switch shows any problems.

             Legacy and Impreza Engines with                  1995 Subaru Legacy - DTC PO325 -
             No Injection Pulse #1 Cylinder                   Knock Sensor Circuit Malfunction
               Built into the fuel injection control            If you encounter a Check Engine
             unit is logic that will shut off the #1          Light with a DTC P0325 on a 1995 Sub-
             injector if the computer believes that it        aru Legacy, check to see if the knock
             can no longer control the Idle Air Con-          sensor mounting bolt has been torqued
             trol valve. Remember this while trying           too tightly upon installation. Also
             to diagnose a “hard” code for the Idle           check the threads of the sensor mount-
             Air Control Valve or a dead miss in              ing bolt and the thread surfaces of the
             number one cylinder due to no injec-             block to see that they are clean and not
             tion at idle. A problem in the Idle Air          corroded. Any corrosion should be
End Wrench

             Control valve circuit can be responsi-           removed before installing the bolt.
             ble. (Component testing shows that it is           The correct mounting bolt torque is
             usually not the valve itself.)                   15-19 ft. lbs.