Opel Frontera UBS. Manual - part 1222

6E–254

ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P1509 IAC System High RPM

T321115

Circuit Description

The powertrain control module (PCM) 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 PCM 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
PCM 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 PCM detect a condition where too high of an idle
speed is present and the PCM 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, VSS, ECT,
EGR, fuel system, MAF, MAP, IAT, canister purge,
injector control or ignition control.

D

Barometric pressure is above 75 kPa.

D

Engine coolant temperature is above 50

°

C (120

°

F).

D

Engine speed is more than 100-200 RPM lower than
desired idle, based upon coolant temperature.

D

The engine has been running for at least 125 seconds.

D

Vehicle speed is less than 1 mph.

D

Canister purge duty cycle is above 10%.

D

Ignition voltage is between 9.5 volts and 16.7 volts.

D

Engine speed is lower than desired idle.

D

All of the above conditions are met for 5 seconds.

Action Taken When the DTC Sets

D

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

D

The PCM 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

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

Diagnostic Aids

Check for the following conditions:

D

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

6E–255

ENGINE DRIVEABILITY AND EMISSIONS

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 5-8840-2312-0 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
PCM:

D

IAC “A” Low

D

IAC “A” High

D

IAC “B” Low

D

IAC “B” High

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

Was a problem found?

—

Verify repair

Go to 

Step 8

5

Visually/physically inspect for 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–256

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 PCM.

IMPORTANT: The replacement PCM must be
programmed,  Refer to 

UBS 98model year Immobilizer

Workshop Manual.

Is the action complete?

—

Verify repair

—

6E–257

ENGINE DRIVEABILITY AND EMISSIONS

Diagnostic Trouble Code (DTC) P1618 Serial Peripheral Interface (SPI) PCM

Interprocessor Communication Error

Circuit Description

The serial peripheral interface (SPI) communication is
used internally by the PCM to send messages between
the engine processor and the automatic transmission
processor.  Included in each message sent between the
two-processors is a checksum of the message.  Both the
engine processor and automatic transmission processor
will compare this check sum value with the calculated
value.  If the checksums don’t match, the processor will
view the new data as being corrupted and ignore the
values.  The processor will then use the previous
message.  The receiving processor will then send a
message to the sending processor informing it that it’s
last message was corrupted.

Conditions for Setting the DTC

D

Battery voltage is above 9.0 V for 2 seconds.

D

The PCM detects an internal program fault (check sum
of data communications error).

D

Check sum fault present for 3 out 6 seconds.

D

No TCM resets for 2 seconds.

Action Taken When the DTC Sets

D

The PCM will flash the “Check Trans” lamp the first
time the fault is detected.

D

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

D

The automatic transmission will operate in the “safety
mode” to protect the mechanical parts of the
transmission.  Shift quality and/or gear changes may
not be normal.

Conditions for Clearing the MIL/DTC

D

DTC P1618 can be cleared by using the Tech 2 “Clear
Info” function or by disconnecting the PCM battery
feed.

DTC P1618 – Serial Peripheral Interface (SPI) PCM Interprocessor

Communication Error

 

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

Is the EEPROM calibration the latest version
available?

—

Go to 

Step 4

Go to 

Step 3

3

Reprogram the PCM with the latest available
calibrations.

Does DTC 1618 re-appear when the 

OBD System

Check is repeated?

—

Go to 

Step 4

Repair

completed

4

Replace the PCM.

IMPORTANT: The replacement PCM must be
programmed.  Refer to 

UBS 98model year Immobilizer

Workshop Manual.

Is the action complete?

—

Verify repair

—