Hummer H1 (2002+). Manual - part 212

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Electrical System 12-74.1

05745159

Digital Ratio Adapter

Location

The digital ratio adapter is located under the center console on
the engine cover, just above the powertrain control module.

Removal

Remove the cup holder from the center console.

Disconnect the two harness connectors from the digital
ratio adapter.

Pull the digital ratio adapter off of the hook and loop and
remove from the center console.

Installation

Install the digital ratio adapter in the center console on the
hook and loop.

Connect the harness connectors to the bottom of the digital
ratio adapter.

Install the cup holder in the center console.

Figure 12-93.1 Digital Ratio Adapter Removal

√

Circuit Description

The speed sensor circuit consists of a magnetic induction type
sensor, a Digital Ratio Adapter (DRA) and wiring. Geared
teeth pressed on the output shaft induce an alternating current
in the sensor. This A/C signal is transmitted to the DRA. The
DRA compensates for various axle ratios and converts the sig-
nal into a digital signals for use by the speedometer, cruise
control, and the PCM. The DRA sends two different signal to

the PCM. Circuit 565 sends a signal of 40 pulses per revolution
of the output shaft to the PCM. This signal is used to control
shift points, line pressure, TCC and diagnostic codes. Circuit
223 sends a signal of 4000 pulses per mile to the PCM. This
signal is used for cruise and DTCs. The DRA sends a separate
signal to the speedometer on circuit 353. This signal is a
128,000 pulse per mile signal.

NOTE:

The above table only applies to 2000 model year vehicles.

01-S12-017

DIGITAL

RATIO

ADAPTER

POWERTRAIN

CONTROL

UNIT

ENGINE

COVER

Digital Ratio Adapter Out Put Signal to Speedometer

Approximate Reading

Input

Ascending

Descending

30 MPH

1066.6 Htz

60 MPH

2133.3 Htz

30 MPH

1066.6 Htz

3-1-01

Section 12 Electrical System

12-74.2

Electrical System

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Figure 12-93.2 Digital Ratio Adapter Wiring Diagram

TWISTED

PAIR

VEHICLE

SPEED

SENSOR

(VSS)

GROUND

VEHICLE

SPEED

SENSOR
RETURN

679 LG

VEHICLE

SPEED

DIGITAL RATIO ADAPTER

CRUISE

CONTROL

REFERENCE

SIGNAL

4000 PPM

SPEEDO

REFERENCE

SIGNAL

00-S12-038

+12 VOLT

IGNITION

SIGNAL

OUTPUT SHAFT

REVOLUTION

SIGNAL

570 BK

POWERTRAIN

CONTROL

MODULE

( PCM )

GROUND

4000 PPM

CRUISE

CONTROL

REFERENCE

SIGNAL

570 BK

565 BR

C29

C28

FUSE

15 AMP

570 BR

239 PK

676 PP

565 BR

353 YL

IGNITION

EXTERIOR
FUSE
BOX

C1-18

C3-P9

SPEEDO

C33

223 DB

40 PULSE

OUTPUT SHAFT
REVOLUTION

SIGNAL

TO PCM

3-1-01

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Electrical System 12-75

05745159

HVAC Main Blower Inoperative ALL BUT High

Step

Action

Value(s)

Yes

Ignition on, blower switch set to Med2, mode dial
set to face. Measure voltage on the yellow
wire(CKT754) at the blower relay. Is voltage
present?

8 -10v

Replace the

blower relay.

Go to step 2.

Ignition on, blower switch set to Med2, mode dial
set to face. Measure voltage on the grey
wire(CKT752) at the blower resistor. Is voltage
present?

12v

Replace blower

resistor.

Go to step 3.

Ignition on, blower switch set to Med2, mode dial
set to face. Measure voltage on the grey
wire(CKT752) at pin C of the 8pin connector on
the back of the HVAC control head. Is voltage
present?

12v

Repair open,

bad connection

or short to

ground in CKTS

751, 752, and

755 between

HVAC control

head and resis-

tor block.

Replace control

head.

HVAC Compressor Inoperative

Step

Action

Value(s)

Yes

Perform On-board diagnostic system check. Is
system functioning properly?

Go to step 2.

Diagnose prob-

lem in on-board

diagnostic sys-

tem first.

Does A/C system have an adequate charge?

Go to step 3.

Diagnose leak

and recharge.

Is engine in an overheated condition?

Cool down and

recheck.

Go to step 4.

Connect scan tool to vehicle. Ignition on, find
misc. tests and command compressor clutch on.
Does clutch come on?

Go to step 10.

Go to step 5.

Disconnect the compressor clutch. Connect a test
lamp to ground, and probe the brown wire at the
clutch connector. Using the scan tool, command
the clutch on. Does the test light come on?

Replace the

compressor

clutch.

Go to step 6.

Remove A/C relay from the exterior fuse box.
Using a DVOM set to measure voltage, ignition
on, check for voltage at cavities 4E and 6E
(CKT400) in the exterior fuse box. Is voltage
present?

12v

Go to step 7.

Repair open,

bad connection

or short in

CKT400

between exte-

rior fuse box

and ignition

switch.

4-1-00

Section 12 Electrical System

12-76

Electrical System

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Using a DVOM set to measure voltage, place the
positive lead on a battery power source. Place the
ground lead in cavity 6F(CKT440). Using the
scan tool, command the compressor clutch on.
Does meter display battery voltage?

12v

Go to step 8.

Go to step 9.

Using a DVOM set to measure resistance. Check
resistance between cavity 4F(CKT348) and the
brown wire(CKT348)at the compressor clutch
connector. Is resistance below specification?

<.2

Ω

Replace com-

pressor relay.

Repair open or

bad connection

in CKT348

between clutch
relay and com-

pressor clutch.

Ignition on, using a DVOM set to measure volt-
age, backprobe pin D5 in C28 at the
PCM(CKT440) with the negative lead. Place the
positive lead on a battery voltage source. Using
the scan tool, command the compressor clutch on.
Does the meter display battery voltage?

12v

Repair open, or

bad connection

in CKT440

between PCM

and A/C clutch

relay.

Replace the

PCM.

Ignition on, locate engine data list, and “A/C
Request”. Turn mode dial on HVAC control head
to MAX A/C. Does scan tool display indicate A/C
request?

Replace PCM.

Go to step 11.

Ignition on, mode dial set to MAX A/C. Using a
DVOM set to measure voltage, backprobe the tan
wire(CKT198) at the temperature cutout switch
on the HVAC unit with the positive probe. Place
the negative lead on a known good ground. Is
voltage present?

12v

Go to step 14.

Go to step 1.

Ignition on, mode dial set to MAX A/C. Using a
DVOM set to measure voltage, backprobe the yel-
low wire(CKT347) at the temperature cutout
switch on the HVAC unit with the positive probe.
Place the negative lead on a known good ground.
Is voltage present?

12v

Replace the

temperature cut-

out switch.

Go to step 13.

Using a DVOM set to measure voltage, ignition
on, mode dial set to MAX A/C, backprobe for
voltage on pin H (CKT347) in the 8 wire connec-
tor at the rear of the HVAC control head. Is volt-
age present?

12v

Repair open,

bad connection

or short in

CKT347

between HVAC

control head and
temperature cut-

out switch.

Replace control

head.

HVAC Compressor Inoperative (Continued)

Step

Action

Value(s)

Yes

4-1-00

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