Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual - part 865

6E–189

3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P1509 (Flash DTC=22) IAC System High RPM

060RW076

Circuit Description

The engine control module (ECM) controls engine idle
speed by adjusting the position of the idle air control (IAC)
motor pintle.  The IAC is a bi-directional stepper motor
driven by two coils.  The ECM applies current to the IAC
coils in steps (counts) to extend the IAC pintle into a
passage in the throttle body to decrease air flow.  The
ECM reverses the current to retract the pintle, increasing
air flow.  This method allows highly accurate control of idle
speed and quick response to changes in engine load.  If
the ECM detect a condition where too high of an idle
speed is present and the ECM is unable to adjust idle
speed by increasing the IAC counts, DTC P1509 will set,
indicating a problem with the idle control system.

Conditions for Setting the DTC

D

No Tech 2 test is being run.

D

None of these DTCs are set:  TP sensor, CMP, CKP,
MAF.

D

Barometric pressure is above 75 kpa.

D

Engine coolant temperature (ECT) is above 75

°

C.

D

Ignition voltage is above 11 volts.

D

The throttle is closed.

D

Engine speed is between 1000 RPM and 6000 RPM.

D

Relation of IAC step and MAF in wrong.

D

All of the above conditions are met for 1 seconds.

Action Taken When the DTC Sets

D

The ECM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.

D

The ECM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.

Conditions for Clearing the MIL/DTC

D

The ECM will turn the MIL “OFF” on the third
consecutive trip cycle during which the diagnostic has
been run and the fault condition is no longer present.

D

A history DTC P1509 will clear after 40 consecutive
warm-up cycles have occurred without a fault.

D

DTC P1509 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the ECM battery
feed.

Diagnostic Aids

Check for the following conditions:

D

Poor connection at ECM or IAC motor – Inspect
harness connectors for backed-out terminals,
improper mating, broken locks, improperly formed or
damaged terminals, and poor terminal-to-wire
connection.

D

Damaged harness – Inspect the wiring for damage.

D

Vacuum leak – Check for a condition that causes a
vacuum leak, such as disconnected or damaged
hoses, leaks at the EGR valve and the EGR pipe to the
intake manifold, leaks at the throttle body, faulty or

6E–190 3.2L ENGINE DRIVEABILITY AND EMISSIONS

incorrectly installed PCV valve, leaks at the intake
manifold, etc.

D

Throttle body – Check for sticking throttle plate.  Also
inspect the IAC passage for deposits or objects which
keep the IAC pintle from fully extending.

Reviewing the Failure Records vehicle mileage since the
diagnostic test last failed may help determine how often
the condition that caused the DTC to be set occurs.  This
may assist in diagnosing the condition.

DTC P1509 –IAC System High RPM

 

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to 

Step 2

Go to 

OBD

System

Check

2

1. Start the engine.
2. Turn all accessories “OFF” (A/C, rear defroster,

etc.).

3. Using a Tech 2, command RPM up to 1500, down to

500, and then up to 1500 while monitoring “Engine
Speed” on the Tech 2.

NOTE: This Tech 2 command may cause the engine to
“cut out” when RPM goes above 1500.  If this occurs,
the “cutting out” will stop when the Tech 2 command for
the test is discontinued, or if the Tech 2 command is
changed to less than 1500 RPM.

Does the “Engine Speed” remain within the specified
value of “Desired Idle” for each RPM command?

±

 50 RPM

No trouble

found.  Go to

Diagnostic

Aids

Go to 

Step 3

3

1. Disconnect the IAC.
2. Install IAC Node Light J 37027 or equivalent.
3. With the engine running, command RPM up to

1500, down to 500, and then up to 1500 while
observing the node light.

NOTE: This Tech 2 command may cause the engine to
“cut out” when RPM goes above 1500.  If this occurs,
the “cutting out” will stop when the Tech 2 command for
the test is discontinued, or if the Tech 2 command is
changed to less than 1500 RPM.

Does each node light cycle red and green (never
“OFF”)?

—

Go to 

Step 5

Go to 

Step 4

4

1. Check the following circuits for an open, short to

voltage, short ground, or poor connections at the
ECM:

D

IAC “A” Low.

D

IAC “A” High.

D

IAC “B” Low.

D

IAC “B” High.

2. If a problem its found, repair as necessary.

Was a problem found?

—

Verify repair

Go to 

Step 8

5

Visually/physically inspect for the following conditions:

D

Vacuum leaks.

D

Throttle plate or throttle shaft for binding.

D

Accelerator and cruise control cables for being
misadjusted or for binding.

D

Faulty, missing, or incorrectly installed PCV
valve.

Do any of the above require a repair?

—

Refer to

appropriate

section for

on-vehicle

service

Go to 

Step 6

6E–191

3.2L ENGINE DRIVEABILITY AND EMISSIONS

DTC P1509 –IAC System High RPM

  (Cont'd)

Step

No

Yes

Value(s)

Action

6

1. Check for a poor connection at the IAC harness

connector.

2. If a problem is found, replace faulty terminals as

necessary.

Was a problem found?

—

Verify repair

Go to 

Step 7

7

Replace the IAC valve.

Is the action complete?

—

Verify repair

—

8

Replace the ECM.

Is the action complete?

—

Verify repair

—

6E–192 3.2L ENGINE DRIVEABILITY AND EMISSIONS

Symptom Diagnosis

Surges and/or Chuggles Symptom

 

Step

Action

Value(s)

Yes

No

1

DEFINITION:
Engine power variation under steady throttle or cruise.
Feels like the vehicle speeds up and slows down with
no change in the accelerator pedal.

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to 

Step 2

Go to 

OBD

System

Check

2

1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is found,

correct the condition as instructed in the bulletin.

Was a bulletin found that addresses the symptom?

—

Verify repair

Go to 

Step 3

3

Was a visual/physical check performed?

—

Go to 

Step 4

Go to

Visual/Physic

al Check

4

Be sure that the driver understands transmission
torque converter clutch and A/C compressor operation
as explained in the owner’s manual.
Inform the customer how the TCC and the A/C clutch
operate.

Is the customer experiencing a normal condition?

—

System OK

Go to 

Step 5

5

1. Check the the fuel control heated oxygen sensors

(HO2S).  The fuel control heated oxygen sensors
(HO2S) should respond quickly to different throttle
positions.  If they don’t, check them for silicon or
other contaminants from fuel or use of improper
RTV sealant.  The sensors may have a white
powdery coating.

Silicon contamination causes a high but false
HO2S signal voltage (rich exhaust indication).
The ECM will then reduce the amount of fuel
delivered to the engine, causing a severe
driveability problem.  For more information, refer
to 

Engine Control Module (ECM) and Sensors.

2. If a problem is found, repair as necessary.

Was a problem found?

—

Verify repair

Go to 

Step 6

6

1. Check the fuel pressure.  Refer to 

Fuel System

Pressure Test.

2. If a problem is found, repair as necessary.

Was a problem found?

—

Verify repair

Go to 

Step 7

7

Monitor the long term fuel trim on the Tech 2.

Is the long term fuel trim significantly in the negative
range (rich condition)?

—

Go to 

Step 8

Go to 

Step 9

8

1. Check items that can cause the engine to run rich.

Refer to 

Diagnostic Aids in DTC P0172 Diagnostic

Support.

2. If a problem is found, repair as necessary.

Was a problem found?

—

Go to 

Step 10

Verify repair