Safety Warning

DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.

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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM & COMPONENT TESTSCOMPUTERIZED ENGINE CONTROLSPOWERTRAIN CONTROL MODULE (PCM) CONNECTOR TERMINAL IDENTIFICATIONPOWERTRAIN CONTROL MODULE (PCM) - 3.4L

1999 GMC Forward Control 5.7 R, Automatic

Powertrain Control Module (Pcm) - 3.4L

1999 GMC Forward Control 5.7 R, AutomaticSECTION Powertrain Control Module (Pcm) - 3.4L

POWERTRAIN CONTROL MODULE (PCM) - 3.4L ⁽¹⁾

Connector

Terminal No.

Wire Color

Function

C1 (Blue)

1 & 2

.....

Not Used

C1 (Blue)

ORG

Fuel Level Output

C1 (Blue)

LT GRN

Shift Solenoid A Control

C1 (Blue)

DK BLU

Cooling Fan High Speed Control

C1 (Blue)

DK GRN

Cooling Fan Low Speed Control

C1 (Blue)

BLK

Camshaft Position PCM Input

C1 (Blue)

PPL/WHT

CKP 3x Reference Signal

C1 (Blue)

LT BLU/BLK

CKP 24x Reference Signal

C1 (Blue)

10 & 11

.....

Not Used

C1 (Blue)

BLK

Engine Coolant Temperature Sensor Ground

C1 (Blue)

ORG/BLK

Manifold Absolute Pressure Sensor Ground

C1 (Blue)

.....

Not Used

C1 (Blue)

TAN

Serial Data

C1 (Blue)

BLK/WHT

PCM Ground

C1 (Blue)

YEL

Intake Air Temperature Sensor Ground

C1 (Blue)

.....

Not Used

C1 (Blue)

PNK

Ignition Voltage

C1 (Blue)

ORG

Battery Voltage

C1 (Blue)

21-27

.....

Not Used

C1 (Blue)

TAN/WHT

HO2S Sensor 2 Signal Low

C1 (Blue)

TAN

HO2S Sensor 1 Signal Low

C1 (Blue)

PPL

TCC Brake Switch

C1 (Blue)

BLK

EGR Valve Ground

C1 (Blue)

GRY

EGR Valve Ground

C1 (Blue)

DK BLU

Knock Sensor Signal

C1 (Blue)

34 & 35

.....

Not Used

C1 (Blue)

BRN

Generator Light Signal

C1 (Blue)

.....

Not Used

C1 (Blue)

LT GRN/WHT

Idle Air Control B High

C1 (Blue)

39-42

.....

Not Used

C1 (Blue)

BLK

Fuel Injector No. 1 Control

C1 (Blue)

YEL/BLK

Shift Solenoid B Control

C1 (Blue)

.....

Not Used

C1 (Blue)

PNK/BLK

Fuel Injector No. 3 Control

C1 (Blue)

LT GRN/BLK

Fuel Injector No. 2 Control

C1 (Blue)

RED/BLK

Reference Low

C1 (Blue)

49-52

.....

Not Used

C1 (Blue)

TAN/BLK

By-Pass

C1 (Blue)

WHT

Ignition Control

C1 (Blue)

DK GRN

4k Pulse Per Mile

C1 (Blue)

BLK/WHT

PCM Ground

C1 (Blue)

BLK/WHT

PCM Ground

C1 (Blue)

.....

Not Used

C1 (Blue)

PPL

Serial Data (Class 2)

C1 (Blue)

BLK/WHT

PCM Ground

C1 (Blue)

PPL

TP Sensor Ground

C1 (Blue)

62 & 63

.....

Not Used

C1 (Blue)

YEL

Vehicle Speed Sensor High

C1 (Blue)

PPL

Vehicle Speed Sensor Low

C1 (Blue)

66 & 67

.....

Not Used

C1 (Blue)

YEL

Transaxle Range Switch Input B

C1 (Blue)

YEL

Mass Airflow Signal

C1 (Blue)

DK BLU

Theft Deterrent Input

C1 (Blue)

ORG/BLK

Required Torque

C1 (Blue)

DK GRN

Cruise Control Inhibit

C1 (Blue)

BLK/WHT

Fuel Injector No. 5 Control

C1 (Blue)

.....

Not Used

C1 (Blue)

DK GRN

Engine Hot Light Control

C1 (Blue)

DK GRN/WHT

EVAP Canister Purge Control

C1 (Blue)

77 & 78

.....

Not Used

C1 (Blue)

YEL/BLK

Fuel Injector No. 6 Control

C1 (Blue)

.....

Not Used

C2 (Red)

.....

Not Used

C2 (Red)

WHT

EVAP Canister Vent Valve Control

C2 (Red)

DK GRN/WHT

Fuel Pump Relay Control

C2 (Red)

RED

EGR Valve Control

C2 (Red)

BRN/WHT

MIL Control

C2 (Red)

BRN/WHT

Low Oil Level Light Control

C2 (Red)

LT BLU/WHT

Intake Air Control A High

C2 (Red)

WHT

Tachometer Output

C2 (Red)

TAN/BLK

Delivered Torque

C2 (Red)

PPL

HO2S Sensor 1 Signal High

C2 (Red)

PPL/WHT

HO2S Sensor 2 Signal High

C2 (Red)

12-15

.....

Not Used

C2 (Red)

WHT

Transaxle Range P

C2 (Red)

.....

Not Used

C2 (Red)

BLK/WHT

Transaxle Range D

C2 (Red)

19-21

.....

Not Used

C2 (Red)

DK GRN/WHT

A/C Request Signal

C2 (Red)

23 & 24

.....

Not Used

C2 (Red)

LT GRN

MAP Sensor Signal

C2 (Red)

YEL

ECT Sensor Signal

C2 (Red)

RED/BLK

A/C Refrigerant Pressure Sensor Signal

C2 (Red)

BRN

EGR Pintle Position Signal

C2 (Red)

29-32

.....

Not Used

C2 (Red)

GRY

Reference Voltage A

C2 (Red)

GRY

Reference Voltage B

C2 (Red)

ORG

Sensor Ground

C2 (Red)

36-38

.....

Not Used

C2 (Red)

DK GRN/WHT

A/C Compressor Clutch Relay Control

C2 (Red)

40 & 41

.....

Not Used

C2 (Red)

LT BLU/BLK

Fuel Injector No. 4 Control

C2 (Red)

.....

Not Used

C2 (Red)

LT BLU/BLK

Intake Air Control Valve A Low

C2 (Red)

45-48

.....

Not Used

C2 (Red)

LT GRN/BLK

Intake Air Control Valve B Low

C2 (Red)

TAN

Intake Air Temperature Sensor Signal

C2 (Red)

51-54

.....

Not Used

C2 (Red)

DK GRN

Fuel Tank Pressure Sensor Signal

C2 (Red)

GRY

Transaxle Range C

C2 (Red)

.....

Not Used

C2 (Red)

BRN

Engine Oil Level Sensor Signal

C2 (Red)

WHT

Cruise Status

C2 (Red)

.....

Not Used

C2 (Red)

RED

Generator Control

C2 (Red)

62-65

.....

Not Used

C2 (Red)

DK BLU

Throttle Position Sensor Signal

C2 (Red)

.....

Not Used

C2 (Red)

YEL/BLK

Transaxle Fluid Temperature Sensor

C2 (Red)

PPL

Fuel Level Input

C2 (Red)

70 & 71

.....

Not Used

C2 (Red)

RED/WHT

CMP Sensor Ignition Voltage

C2 (Red)

BLK

CMP Sensor Ground

C2 (Red)

74-77

.....

Not Used

C2 (Red)

BRN

TCC PWM Solenoid Control

C2 (Red)

TAN/BLK

TCC Enable Solenoid

C2 (Red)

.....

Not Used

⁽¹⁾	See Figure.

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.
• Brakes feel soft, pull hard to one side, or make grinding noises.
• The engine overheats, stalls repeatedly, or misfires under load.
• You are missing required tools, torque specs, or safe lifting equipment.
• You are not confident in the next step or safety outcome.