©
2001 Caterpillar
All Rights Reserved
Printed in U.S.A.
RENR1368-04
May 2001
3126B and 3126E Truck Engine
Electrical System
BKD1-UP
1AJ1-UP
8YL1-UP
CKM1-UP
7AS1-UP
8SZ1-UP
9SZ1-UP
CRP1-UP
A
MPH
15
5
0
25
45
35 55
65
75
85
RPM X 1000
5
10
15
20
25
30
Engine
Control
Module
Cab Diagnostic Connector
Batteries
- 12 V +
Cruise Control On/Off &
Set/Resume Switches
Accelerator Pedal Position Sensor
Ignition Key Switch
Clutch and Service Brake Switches
6 HEUI Injectors
Injection Actuation Pressure Control Valve
(IAPCV)
Top Camshaft Speed/Timing Sensor
Bottom Camshaft Speed/Timing Sensor
Injection Actuation Pressure Sensor
Boost Pressure Sensor
Atmospheric Pressure Sensor
Oil Pressure Sensor
(Optional)
(Optional)
(Specific Ratings Only)
Coolant Temperature Sensor
Intake Manifold Air Temperature Sensor
Intake Air Heater Relay
Intake Air Heater
Coolant Level Sensor
Oil Level Switch
Check Engine Lamp
Warning Lamp
Speedometer & Tachometer
A/C High Pressure Switch
Cooling Fan
Vehicle Speed
Sensor
PTO Accelerator
Position Sensor
Fast Idle Enabled Lamp
Or Wait To Start Lamp
PTO Switch On Lamp
Fast Idle Enable Switch
Exhaust Brake On/Off Switch
PTO On/Off & PTO
Set/Resume Switches
Transmission Neutral Switch
AT/MT/HT Transmission Relay
Exhaust Brake
Intake Air Heater Lamp
Caterpillar Installed
OEM Installed
PID-FMI Description Flash
Codes
PID-FMI Description Flash
Codes
0-00 No Detected Faults 55 102-04 Boost Press Sensor Short Circuit 25
1-11 Cylinder 1 Fault 72 102-07 Excessive Boost Pressure 25
2-11 Cylinder 2 Fault 72 105-03 Inlet Manifold Air Temp Sensor Open Circuit 38
3-11 Cylinder 3 Fault 73 105-04 Inlet Manifold Air Temp Sensor Short Circuit 38
4-11 Cylinder 4 Fault 73 108-03 Atmospheric Press Sensor Open Circuit 26
5-11 Cylinder 5 Fault 74 108-04 Atmospheric Press Sensor Short Circuit 26
6-11 Cylinder 6 Fault 74 110-00 High Coolant Temp Warning 61
22-13 Check Timing Sensor Calibration 42 110-03 Coolant Temp Sensor Open Circuit 27
30-08 Invalid PTO Throttle Signal 29 110-04 Coolant Temp Sensor Short Circuit 27
30-13 PTO Throttle Sensor Calibration 29 110-11 Very High Coolant Temp 61
41-03 8 Volt Supply Above Normal 21 111-01 Low Coolant Level Warning 62
41-04 8 Volt Supply Below Normal 21 111-02 Coolant Level Sensor Fault 12
42-11 Injection Actuation Press
Control Valve Driver Fault
18 111-11 Very Low Coolant Level 62
43-02 Ignition Key Switch Fault 71 164-00 Injection Actuation Press Out of Range 17
64-02 Loss of Engine RPM Signal on Engine
Speed and Timing Sensor Number 2
34 164-02 Injection Actuation Press Sensor Erratic 15
64-11 No Pattern on Engine Speed
and Timing Sensor Number 2
34 164-03 Injection Actuation Press Open Circuit 15
70-05 Inlet Air Heater Open Circuit 49 164-04 Injection Actuation Press Short Circuit 15
70-06 Inlet Air Heater Short Circuit 49 164-11 Injection Actuation Press System 39
71-00 Idle Shutdown Override 01 168-02 Intermittent Battery Power to the ECM 51
71-01 Idle Shutdown Occurrence 47 190-00 Engine Overspeed Warning 35
71-14 PTO Shutdown Occurrence 47 190-02 Loss of RPM Signal on Engine Speed
and Timing Sensor Number 1
34
84-00 Vehicle Overspeed Warning 41 190-11 No Pattern on Engine Speed
and Timing Sensor Number 1
34
84-01 Loss of Vehicle Speed Signal 31 224-11 Theft Deterrent Enabled 00
84-02 Invalid Vehicle Speed Signal 36 224-14 Engine Cranking / Theft Deterrent Enabled 00
84-08 Vehicle Speed Out of Range 36 231-11 J1939 Data Link Fault 58
84-10 Vehicle Speed Rate of Change 36 232-03 5 Volt Supply Above Normal 21
91-08 Invalid Throttle Signal 32 232-04 5 Volt Supply Below Normal 21
91-13 Throttle Sensor Calibration 28 246-11 Service Brake Switch Number 1 Fault 00
100-03 Oil Press Sensor Open Circuit 24 247-11 Service Brake Switch Number 2 Fault 00
100-04 Oil Press Sensor Short Circuit 24 252-11 Incorrect Engine Software 59
100-11 Very Low Oil Press 46 253-02 Check Customer or System Parameters 56
102-03 Boost Press Sensor Open Circuit 25 253-14 Truck Manuf. Parameter Not Programmed 56
Diagnostic Code Listing
HarnessSide
HarnesECM Connector P1
ECM Connector P2
sSide
ECMSide
ECMSide
ECM Connectors
DT Connector Receptacle DT Connector Plug
Plug Wedge
Plug Wedge
Plug Wedge
Receptacle Wedge
Receptacle Wedge
Receptacle Wedge
HD Connector Receptacle
HD Connector Plug
Pin Contact
Sealing Plug
Socket Contact
Speed/Timing Sensor Connectors
150 Series Receptacle
IAPCV Connector
150 Series Plug
G809-GN
G828-WH
A
B
INJECTION ACTUATION
PRESSURE CONTROL VALVE
(IAPCV)
J500 P500
J400 P400
B
A
TOP CAMSHAFT SPEED/TIMING-
TOP CAMSHAFT SPEED/TIMING+
BOTTOM CAMSHAFT SPEED/TIMING-
BOTTOM CAMSHAFT SPEED/TIMING+
E963-BK
E964-WH
49
48
13
19
20
21
28
29
30
59
58
31
43
51
22
23
56
57
65
66
69
8
G856-WH
G857-YL
A
B
TOP CAMSHAFT ENGINE
SPEED/TIMING SENSOR
TOP CAMSHAFT SPEED/TIMING-
TOP CAMSHAFT SPEED/TIMING+
J401 P401
J402 P402
B
A
BOTTOM CAMSHAFT SPEED/TIMING-
BOTTOM CAMSHAFT SPEED/TIMING+
BOTTOM CAMSHAFT ENGINE
SPEED/TIMING SENSOR
1
2
ENGINE COOLANT
TEMPERATURE
995-BU
G833-PK
J100 P100
ENGINE COOLANT TEMPERATURE
ENGINE TEMPERATURE SENSOR COMMON
ENGINE INTAKE MANIFOLD AIR TEMPERATURE
ENGINE TEMPERATURE SENSOR COMMON
J103 P103
C967-BU
G833-PK
ENGINE INTAKE
MANIFOLD AIR
TEMPERATURE
1
2
995-BU
C967-BU
G883-GN
G458-GY
G833-PK
C
B
A
G849-BR
G829-GN
G828-WH
A746-PK
G849-BR
A747-GY
G829-GN
P204 J204
ENGINE OIL PRESSURE SENSOR
ENGINE OIL PRESSURE SENSOR COMMON
ENGINE OIL PRESSURE SENSOR +5V
ENGINE ATMOSPHERIC
PRESSURE
NOTE A
GN
YL
OR
ENGINE INJECTION
ACTUATION
PRESSURE
ENGINE INJECTION ACTUATION PRESS.
ENGINE PRESSURE SENSOR COMMON
ENGINE PRESSURE SENSOR +5V
GN
YL
OR
P201 J201
994-GY
G827-BU
G826-BR
A
B
C
J200 P200
A746-PK
G829-GN
G828-WH
A
B
C
SENSOR
ENGINE BOOST
PRESSURE
ENGINE BOOST PRESSURE
ENGINE PRESSURE SENSOR COMMON
ENGINE PRESSURE SENSOR +5V
GN
YL
0R
COMPONENTS ARE SHOWN WITH THE KEY OFF
UNLESS OTHERWISE SPECIFIED:
ALL WIRES TO BE 18 AWG OR LARGER SAE J1560 TYPE TXL
OR EQUIVALENT. FOR TWISTED PAIR SPECIFICATION SEE J1708.
INTAKE AIR HEATER RELAY
ENGINE COOLANT TEMPERATURE
ENGINE OIL LEVEL SWITCH
INPUT #16
ENGINE INTAKE MANIFOLD AIR TEMPERATURE
ENGINE TEMPERATURE SENSOR COMMON
ENGINE ATMOSPHERIC PRESSURE
ENGINE PRESSURE SENSOR COMMON
ENGINE PRESSURE SENSOR +5V
IAP CONTROL VALVE
IAP CONTROL VALVE COMMON
ENGINE BOOST PRESSURE
ENGINE INJECTION ACTUATION PRESSURE
ECM GROUND STRAP
G854-PK
G855-PU
TO ECM
MOUNTING
BOLT
ENGINE HARNESS CONNECTOR
C987-RD
G850-BU
P648
NOTE A
A
B
K995-OR
G850-BU
C987-RD
1
2
ENGINE TIMING CALIBRATION PROBE+
ENGINE TIMING CALIBRATION PROBE-
TO ENGINE CYLINDER HEAD
(NOT CYLINDER HEAD GROUND STUD)
INTAKE AIR
HEATER
G850-BU
P2 J2
ENGINE TIMING CALIBRATION PROBE+
ENGINE TIMING CALIBRATION PROBE-
J501 P501
N/O
RELAY
32
35
9
34
26
18
10
11
12
15
16
17
24
25
41
42
50
52
53
60
33
40
27
6
7
14
3
2
INJECTOR
CYLINDER
NO.5
1
63
64
4
5
61
62
70
INJECTOR
CYLINDER
NO.6
J306 P306J305 P305
J304 P304J303 P303
J302 P302
L984-OR
INJECTOR
CYLINDER
NO.4
INJECTOR HARNESS GROMMET
J301 P301
INJECTOR
CYLINDER
NO.1
A704-GN
A705-BU
A703-BR
A702-PU
A701-GY
L985-YL
L984-OR
A706-GY
L985-YL
L983-WH
L983-WH
INJECTOR
CYLINDER
NO.3
INJECTOR
CYLINDER
NO.2
P300 J300
L983-WH
L984-OR
L985-YL
A706-GY
A705-BU
A704-GN
A703-BR
A702-PU
A701-GY
INJECTOR COMMON CYLINDERS 1 & 2
INJECTOR COMMON CYLINDERS 3 & 4
INJECTOR COMMON CYLINDERS 5 & 6
INJECTOR CYLINDER 6
INJECTOR CYLINDER 5
INJECTOR CYLINDER 4
INJECTOR CYLINDER 3
INJECTOR CYLINDER 2
INJECTOR CYLINDER 1
44
45
46
55
54
39
38
37
36
47
67
68
12
11
10
9
8
7
6
5
4
3
2
1
3126B & 3126E ENGINE HARNESS WIRING DIAGRAM
SENSOR
SENSOR
1
2
ENGINE OIL LEVEL
SWITCH
NOTE A
G458-GY
G829-GN
J802 P802
ENGINE OIL LEVEL
ENGINE OIL LEVEL COMMON
SENSOR
SENSOR
ENGINE ATMOSPHERIC PRESSURE
ENGINE PRESSURE SENSOR COMMON
ENGINE PRESSURE SENSOR +5V
GN
YL
OR
P203 J203
A747-GY
G829-GN
G828-WH
A
B
C
994-GY
ENGINE OIL PRESSURE SENSOR
ENGINE OIL
PRESSURE
NOTE A
SENSOR
G827-BU
G826-BR
ENGINE OIL PRESSURE SENSOR COMMON
ENGINE OIL PRESSURE SENSOR +5V
NOTE A
FLYBACK
DIODE
EXHAUST BRAKE
SOLENOID
TO ALLISON AT/MT/HT SHIFT
MODULATOR FOR AUTOMATIC
TRANSMISSIONS
COOLING FAN SOLENOID
NOTE A
INTAKE AIR
HEATER LAMP
J648
100A WITH 130A PEAK AT 11V
C987-RD
SENSOR ACCELERATOR
PEDAL POSITION
BK
RD
WH
J403 P403
ACCELERATOR PEDAL SENSOR/SWITCH SENSOR COMMON
+8 V
ACCELERATOR PEDAL POSITION
B
A
C
L901-GY
C977-BU
G879-OR
H795-PK
H795-PK
A/C HIGH PRESSURE SWITCH N/C
E971-GN
450-YL
451-BR
SIGNAL+
SIGNAL-
NOTE A
TACHOMETER
NOTE A
INPUT SENSOR COMMON #1
CLUTCH PEDAL POSITION SWITCH
+5V
E793-BU
E794-YL
INPUT #12
INPUT #11
INPUT #7
ENGINE COOLANT LEVEL NORMAL
ENGINE COOLANT LEVEL LOW
VEHICLE SPEED IN POSITIVE
VEHICLE SPEED IN NEGATIVE
INPUT #8 (REMOTE ACCELERATOR)
20A
14 AWG GXL
14 AWG GXL
14 AWG GXL
14 AWG GXL
AP SENSOR/SWITCH SENSOR COMMON
+8V
ACCELERATOR PEDAL POSITION
OUTPUT #5
18
22
23
2
46
49
54
PASSIVE MAGNETIC
VEHICLE SPEED
SENSOR
G808-BU
G809-GN
H795-PK
H795-PK
SET/RESUME SWITCH
ENGINE
BLOCK
62
24
409-OR
E971-GN
E793-BU
E794-YL
A249-BK
K990-GN
K900-YL
A249-BK
K990-GN
K900-YL
J906-BR
COMPONENTS WITHIN THIS AREA ARE CATERPILLAR PROVIDED
CLUTCH PEDAL POSITION SWITCH N/C
SERVICE BRAKE PEDAL POSITION SWITCH N/C
(PEDAL RELEASED POSITION)
NOTE A
NOTE A
NOTE A
NOTE A
NOTE A
NOTE A
NOTE A
CRUISE CONTROL ON/OFF SWITCH
CHECK ENGINE
LAMP
WARNING LAMP
+BAT.
-BAT.
NOTE A
NOTE A
J1587 -
J1587 +
J1939 -
J1939 SHIELD
J1939 +
1
2
J
H795-PK
A
B
H
9 PIN CAB
CONNECTOR
G
F
E
D
C
5
4
66
11
41
69
32
33
68
VEHICLE HARNESS CONNECTOR
H795-PK
C985-BU
C986-BR
G837-YL
B
A
659-PK
L994-YL
G880-PK
K998-BU
CIRCUITS WITHIN THIS AREA ARE RECOMMENDATIONS
SERVICE BRAKE PEDAL POSITION SWITCH
INPUT #5
INPUT #13
INPUT #6
+BAT.
NOTE A
(TRANSMISSION IN GEAR)
START
ON
OFF
NOTE A
45
55
47
64
6
C992-PU
G842-GY
G882-WH
G843-OR
K995-OR
C987-RD
993-BR
F713-OR
STARTER
MOTOR
(12V)
FLYBACK
DIODE
NOTE A
CRUISE CONTROL ON/OFF SWITCH
INPUT #3
INPUT #4
59
60
7
BATTERY 2
C975-WH
K982-YL
G841-GN
N/O
RELAY
H795-PK
C985-BU
C986-BR
SET
RESUME
INPUT #1 (PTO ON/OFF SWITCH)
INPUT #2
INPUT #18
OUTPUT #8
C978-BR
C979-OR
C977-BU
C992-PU
C975-WH
35
44
56
58
40
21
C978-BR
C979-OR
K999-GN
K980-PK
L902-GN
G840-PU
KEY SWITCH
659-PK
GROUND
L994-YL
ALTERNATOR
-
12V
+
-
12V
+ +
P1 J1
12V
-
BATTERY 3
BATTERY 1
G808-BU
G845-PU
J1587 DATA LINK NEGATIVE
J1587 DATA LINK POSITIVE
J1939 DATA LINK SHIELD
J1939 DATA LINK NEGATIVE
J1939 DATA LINK POSITIVE
IGNITION KEY SWITCH
UNSWITCHED +BATTERY
UNSWITCHED +BATTERY
-BATTERY
-BATTERY
OUTPUT #6
OUTPUT #7
52
53
65
67
19
20
51
101-RD
101-RD
229-BK
229-BK
G838-BR
G839-BU
9
8
42
34
50
1
14
70
25
TACHOMETER POSITIVE
TACHOMETER NEGATIVE
38
39
57
43
G844-PK
C983-WH
C984-YL
450-YL
451-BR
C974-PU
C973-GN
C974-PU
C973-GN
SIGNAL+
SIGNAL-
NOTE A
SPEEDOMETER
NOTE A
H795-PK
FAST IDLE ENABLE SWITCH
L902-GN
N/O MOMENTARY SWITCH
NOTE A
G880-PK
FAST IDLE
ENABLED LAMP
OR
WAIT TO
START LAMP
N/O MOMENTARY SWITCH
G844-PK
SPEEDOMETER POSITIVE
EXHAUST BRAKE ON/OFF SWITCH
SPEEDOMETER NEGATIVE
INPUT SENSOR COMMON #2
INPUT #14
36
37
27
26
3
17
DIAGNOSTIC ENABLE SWITCH
H795-PK
(PEDAL RELEASED POSITION)
+BAT.
29
28
30
31
48
61
10
12
13
15
16
63
NOTE A
G882-WH
SERVICE BRAKE PEDAL POSITION SWITCH #2 N/O
(PEDAL RELEASED POSITION)
WARNING LAMP
CHECK ENGINE LAMP
ENGINE CONTROL MODULE ENGINE CONTROL MODULE
OUTPUT #1
OUTPUT #9
TRANSMISSION NEUTRAL SWITCH N/O
409-OR
OUTPUT #2
OUTPUT #3
OUTPUT #4
E718-PK
E991-GY
G836-WH
C981-GY
3126B & 3126E OEM VEHICLE HARNESS WIRING DIAGRAM
NOTE A: THIS IS AN OPTIONAL FEATURE NOT INSTALLED ON ALL VEHICLES.
NOTE A: THIS IS AN OPTIONAL FEATURE NOT INSTALLED ON ALL VEHICLES.
NOTE A
INPUT SIGNAL WIRES TO ECM
OUTPUT SIGNAL WIRES FROM ECM
SENSOR SUPPLY VOLTAGE
(+) BATTERY SUPPLY WIRES
SIGNAL PLUS
(-) BATTERY / SENSOR RETURN
SIGNAL MINUS
E965-BU
E966-YL
EXHAUST BRAKE ON/OFF SWITCH
INJECTOR HARNESS
GROMMET
INJECTION ACTUATION
PRESSURE SENSOR
INLET AIR HEATER
INLET AIR
TEMPERATURE
SENSOR
ATMOSPHERIC
PRESSURE
SENSOR
(SELECT RATINGS ONLY)
BOOST
PRESSURE
SENSOR
ENGINE HARNESS
CONNECTOR
J2/P2
ENGINE GROUND
STUD CONNECTION
VEHICLE HARNESS
CONNECTOR
J1/P1
INJECTION ACTUATION
PRESSURE CONTROL
VALVE
(IAPCV)
ENGINE SPEED/TIMING
SENSORS
COOLANT
TEMPERATURE
SENSOR
OIL PRESSURE
SENSOR
(OPTIONAL)
OIL LEVEL
SWITCH
(OPTIONAL)
ENGINE
CONTROL
MODULE
INJECTOR HARNESS
GROMMET
INLET AIR
HEATER
RELAY
INJECTION ACTUATION
PRESSURE SENSOR
INLET AIR HEATER
TOP VIEW
LEFT SIDE VIEW
INLET AIR
TEMPERATURE
SENSOR
ATMOSPHERIC
PRESSURE
SENSOR
BOOST
PRESSURE
SENSOR
ENGINE GROUND
STUD CONNECTION
INJECTION ACTUATION
PRESSURE CONTROL
VALVE
B
A
B
A
B
A
B
A
B
A
B
A
