Hummer H1 (2002+). Manual - part 295

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PCM/Tech 1 Scan Tool 113

05745159

DTC P1641 Malfunction Indicator Lamp
(MIL) Control Circuit

Circuit Description

A dash light is illuminated by the PCM if diagnostics have de-
tected certain errors related to the engine performance or en-
gine sensor status. Illumination is accomplished by the PCM
providing a ground path for the lamp circuit. This is a type D
DTC.

Conditions for Setting the DTC

• MIL requested “ON”.

• Voltage at the MIL control circuit is greater than 0 volts.

• MIL requested “OFF”.

• Voltage at the MIL control circuit is greater than 0 volts.

Action Taken When the DTC Sets

Will not turn “ON” the MIL.

Conditions for Clearing the MIL/DTC

• A History DTC will clear when forty consecutive

warm-up cycles that the diagnostic does not fail (coolant
temperature has risen 5°C (40°F) from start up coolant
temperature and engine coolant temperature exceeds
71°C (160°F) that same ignition cycle).

• Use of a scan.

Diagnostic Aids

A faulty bulb or the control circuit shorted to ground will cause
a P1641 to set.

Test Description

Number(s) below refer to the number(s) on the diagnostic ta-
ble.

3. This test will check the control circuit for a short to ground.

5. This test will check the control circuit for an open.

FUSE 2D
20 AMP
INTERIOR

STS

LAMP

MIL

LAMP

FUSE 3A
20 AMP
EXTERIOR

HOT AT
ALL TIMES

HOT IN RUN
AND START

HOT IN RUN

AND START

FUSE 4B
5 AMP
INTERIOR

FUSE 1H
5 AMP
INTERIOR

DLC

POWERTRAIN

CONTROL

MODULE

SERIAL DATA

CLASS II

MIL

CONTROL

STS LAMP

CONTROL

914 PP

59 BK

C28-C8

570 BK

C28-D7

C28-D6

GROUND

570 BK

BATT

IGN

C28-C13

C28-D13

C28-C12

C28-C11

C28-D11

C29-B3

537 OR

239 PK

C1-10

C10-J

C10-H

C10-C

C3-G5

C3-F3

C1-25

C1-28

C28-C14

658 BR

714 RD

STATUS
CENTER

HOT AT

ALL TIMES

9-S12-064

554 GRY

114

PCM/Tech 1 Scan Tool

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DTC P1641 - Malfunction Indicator Lamp (MIL) Control Circuit

Step

Action

Value(s)

Yes

Important:

Before clearing DTC(s) use the scan tool “Capture Info” to

record freeze frame and failure records for reference, as data will be lost
when “Clear Info” function is used.

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

—

Go to Step 2.

Go to OBD

System Check.

1. Scan tool connected.
2. Ignition “ON” engine “OFF”.

Is the MIL “OFF”?

—

Go to Step 3.

Go to Step 5.

1. Ignition “OFF”.
2. Disconnect the blue 32 way PCM electrical connector.

3. Ignition “ON” engine “OFF”.

Is the MIL “ON”?

—

Go to Step 4.

Go to Step 6.

MIL control circuit is shorted to ground.

Is the action complete?

—

Go to Step 7.

—

1. Check the MIL control circuit for the following:

• opens

• poor connection at PCM

• faulty bulb

• faulty fuse.

Was a problem found?

—

Go to Step 7.

Go to Step 6.

Replace the faulty PCM. Notice: If the PCM is faulty, the new PCM must
be programmed. Go to PCM replacement and programming procedures.
Is the action complete?

—

Go to Step 7.

—

1. Using the Scan Tool, select “DTC”, “Clear Info”.
2. Start engine and idle at normal operating temperature.

3. Select “DTC”, “Specific”, then enter the DTC number which was set.

4. Operate vehicle within the conditions for setting this DTC as specified in

the supporting text.

Does the Scan Tool indicate that this diagnostic Ran and Passed?

—

Go to Step 8.

Go to Step 2.

Using the Scan Tool, select “Capture Info”, “Review Info”.
Are any DTCs displayed that have not been diagnosed?

—

Go to the

applicable

DTC table

System OK.

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PCM/Tech 1 Scan Tool 115

05745159

DTC P1643 Wait to Start Lamp Control Circuit

Circuit Description

A dash light (Wait To Start) is illuminated by the PCM when
the glow plugs are commanded ON. When the PCM is com-
manding the Wait To Start lamp ON, the voltage potential of
the circuit will be low (near 0 volts). When the PCM is com-
manding the Wait To Start lamp OFF, the voltage potential of
the circuit will be high (near battery volts). The primary func-
tion of the PCM is to supply the ground for the Wait To Start
lamp circuit. This is a type B DTC.

Conditions for Setting the DTC

• Wait To Start lamp requested ON.

• Voltage on Wait To Start tamp circuit high (near battery

volts).

• Wait To Start lamp requested OFF.

• Voltage on Wait To Start lamp control circuit low (near

0 volts).Action Taken When the DTC Sets

Action Taken When the DTC Sets

No Wait To Start lamp.

Conditions for Clearing the MIL/DTC

• The PCM will turn the MIL off after three consecutive

trips without a fault condition.

• A History DTC will clear when forty consecutive

warm-up cycles that the diagnostic does not fail (coolant
temperature has risen 5° C (40° F) from start up coolant
temperature and engine coolant temperature exceeds
71° C (160° F) that same ignition cycle.

• Use of a Scan tool.

Diagnostic Aids

A faulty bulb or the control circuit shorted to ground will cause
a P1643 to set.

Test Description

5. Repeat the command as many times as necessary (when

glow plugs are commanded ON by the scan tool, an internal
PCM timer protects the glow plugs from damage by cycling
them ON for 3 seconds and OFF for 12 seconds. After the
12 seconds has elapsed, the glow plugs can be commanded
ON again).

9. If no trouble is found in the control circuit or the connection

at the PCM, the PCM maybe malfunctioning, however, this
is an extremely unlikely failure.

FUSE 3A
20 AMP
EXTERIOR

HOT IN RUN
AND START

GLOW PLUG
RELAY

IGN

POWER

FUSIBLE
LINK

AIT

WAIT TO START
LAMP CONTROL

C9-J

C9-A

C3-D1

C1-27

C28-C7

GLOW PLUGS RH

GLOW PLUG

RELAY

CONTROL

GLOWPLUG

FEEDBACK

SIGNAL

POWERTRAIN
CONTROL
MODULE
(PCM)

C27-D7

C27-C6

30 GY

466 YL

C5-A4

338 DB

C3-N7

RIGHT
BANK
OUTPUT

00-S12-011

B+

C5-C11

C5-B4

GLOW PLUGS LH

BATT +

LEFT

BANK

OUTPUT

RH STATUS

CENTER

506 LB

239 PK

STARTER

POS. STUD

FUSE 4B
5 AMP
INTERIOR
FUSE BOX

IGNITION

SWITCH

116

PCM/Tech 1 Scan Tool

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DTC P1643 Wait to Start Lamp Control Circuit

Step

Action

Value(s)

Yes

Important:

Before clearing DTC(s) use the scan tool “Capture Info” to

record freeze frame and failure records for reference, as data will be lost
when “Clear Info” function is used.

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

Go to step 2

Go to Power-

train OBD

System
Checke

1. Turn the ignition ON leaving the engine OFF.
2. Using a scan tool, command the Glow Plug system ON.

Does the lamp turn ON?

Go to step 3

Go to step 4

The DTC is intermittent. If no additional DTCs are stored, refer to Diag-
nostic Aids. If additional DTCs were stored refer to those tables(s)

Are additional DTCs stored?

Go to the

applicable

DTC table

Go to Diag-

nostic Aids

1. Turn the ignition OFF.
2. Disconnect the PCM connector containing the Wait To Start lamp con-

trol circuit.

3. Turn the ignition ON leaving the engine OFF.

Is the lamp OFF?

Go to step 5

Go to step 7

With a fused jumper wire connected to ground, probe the Wait to Start
lamp control circuit in the PCM harness connector.

Is the lamp ON?

Go to step 6

Go to step 8

Check the connections at the PCM.

Was a repair performed?

Go to step 10

The Wait To Start lamp control circuit is shorted to ground, repair as nec-
essary.

Is the action complete?

Go to step 10

Check the Wait To Start circuit for the following:

• Open ignition feed to the bulb

• malfunctioning bulb

• Control circuit open or shorted to B+

Was a repair performed?

Go to step 10

Replace the PCM.

Is the action complete?

Go to step 10

1. Using the Scan Tool, select “DTC”, “Clear Info”.
2. Start engine and idle at normal operating temperature.

3. Select “DTC”, “Specific”, then enter the DTC number which was set.

4. Operate vehicle within the conditions for setting this DTC as specified

in the supporting text.

Does the Scan Tool indicate that this diagnostic Ran and Passed?

Go to step 11

Go to step 2

Does the Scan tool display any additional undiagnosed DTCs?

Go to the

Applicable

DTC table

System OK

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