
TEST ACTION APPLICABILITY
6 Turn the ignition on.
With the DRB, actuate the Low Speed Rad Fan and observe the Radiator Fans.
NOTE: Both Radiator Fans should operate at low speed.
Did both Radiator Fans operate as they should?All
Ye s®Go To 7
Fans do not operate on Low
Go To 15
Fan 1 on High/Fan 2 not on
Go To 23
Fan 1 not on/Fan 2 on High
Go To 26
7 Turn the ignition on.
With the DRB, actuate the High and Low Speed Rad Fans at the same time and
observe the Radiator Fans.
NOTE: Both Radiator Fans should operate at high speed.
Did both Radiator Fans operate as they should?All
Ye s®The test is complete. Ensure the ECM will turn the fans on when
the engine is hot.
Perform ROAD TEST VERIFICATION - VER-2.
Fan 1 on High/Fan 2 not on
Go To 8
Fan 1 not on/Fan 2 on High
Go To 11
8 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 2 harness connector.
Using a 12-volt test light connected to ground, check the Fused B+ circuit.
Did the test light illuminate brightly?All
Ye s®Go To 9
No®Repair the Radiator Fan Relay No. 2 Fused B+ circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
9 Turn the ignition off.
Install a substitute relay in place of Radiator Fan Relay No. 2.
Turn the ignition on.
With the DRB, actuate the High Speed Fan Relay.
Does Radiator Fan No. 2 cycle on and off?All
Ye s®Replace Radiator Fan Relay No. 2.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 10
188
DRIVEABILITY - DIESEL
*CHECKING THE ELECTRIC RADIATOR FAN OPERATION ÐContinued

TEST ACTION APPLICABILITY
10 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 2 harness connector.
Disconnect the Radiator Fan No. 2 harness connector.
Measure the resistance of the Radiator Fan Relay No. 2 and No. 3 Common Output
circuit from Radiator Fan Relay No. 2.
Is the resistance below 5.0 ohms?All
Ye s®Test Complete.
No®Repair the Radiator Fan Relay No. 2 and No. 3 Common Output
circuit from Radiator Fan Relay No. 2 for an open.
Perform ROAD TEST VERIFICATION - VER-2.
11 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Using a 12-volt test light connected to ground, check the Fused B+ circuit.
Did the test light illuminate brightly?All
Ye s®Go To 12
No®Repair the Radiator Fan Relay No. 3 Fused B+ circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
12 Turn the ignition off.
Install a substitute relay in place of Radiator Fan Relay No. 3.
Turn the ignition on.
With the DRB, actuate the High Speed Fan Relay and then actuate the Low Speed
Fan Relay.
Does Radiator Fan No. 2 cycle on and off and then both fans cycle on and off when
requested?All
Ye s®Replace Radiator Fan Relay No. 3.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 13
13 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the Radiator Fan No. 2 harness connector.
Using a 12-volt test light connected to 12-volts, check the Radiator Fan Relay No. 3
Ground circuit at the Radiator Fan Relay No. 3 harness connector.
Did the test light illuminate brightly?All
Ye s®Go To 14
No®Repair the Radiator Fan Relay No. 3 Ground circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
14 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the ECM harness connectors.
Measure the resistance of the High Speed Radiator Fan Dual Relay Control circuit.
Is the resistance below 5.0 ohms?All
Ye s®Test Complete.
No®Repair the High Speed Radiator Fan Dual Relay Control circuit
for an open.
Perform ROAD TEST VERIFICATION - VER-2.
189
DRIVEABILITY - DIESEL
*CHECKING THE ELECTRIC RADIATOR FAN OPERATION ÐContinued

TEST ACTION APPLICABILITY
15 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 1 harness connector.
Using a 12-volt test light connected to ground, check the Fused B+ circuit.
Did the test light illuminate brightly?All
Ye s®Go To 16
No®Repair the Radiator Fan Relay No. 1 Fused B+ circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
16 Turn the ignition off.
Install a substitute relay in place of Radiator Fan Relay No. 1.
Turn the ignition on.
With the DRB, actuate the Low Speed Fan Relay.
Do both Radiator Fans cycle on and off?All
Ye s®Replace Radiator Fan Relay No. 1.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 17
17 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 1 harness connector.
Disconnect the Radiator Fan No. 1 harness connector.
Using a 12-volt test light connected to 12-volts, check the Radiator Fan Relay No. 1
Output circuit in the Radiator Fan Relay No. 1 harness connector.
Did the test light illuminate?All
Ye s®Repair the Radiator Fan Relay No. 1 Output circuit for a short to
ground.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 18
18 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the Radiator Fan No. 2 harness connector.
Using a 12-volt test light connected to 12-volts, check the Radiator Fan Relay No. 3
Ground circuit at the Radiator Fan Relay No. 3 harness connector.
Did the test light illuminate brightly?All
Ye s®Go To 19
No®Repair the Radiator Fan Relay No. 3 Ground circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
19 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 1 harness connector.
Disconnect the Radiator Fan No. 1 harness connector.
Measure the resistance of the Radiator Fan Relay No. 1 Output circuit.
Is the resistance below 5.0 ohms?All
Ye s®Go To 20
No®Repair the Radiator Fan Relay No. 1 Output circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
190
DRIVEABILITY - DIESEL
*CHECKING THE ELECTRIC RADIATOR FAN OPERATION ÐContinued

TEST ACTION APPLICABILITY
20 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the Radiator Fan No. 1 harness connector.
Measure the resistance of the Radiator Fan No. 1 Control circuit.
Is the resistance below 5.0 ohms?All
Ye s®Go To 21
No®Repair the Radiator Fan No. 1 Control circuit for an open.
Perform ROAD TEST VERIFICATION - VER-2.
21 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the Radiator Fan No. 2 harness connector.
Measure the resistance of the Radiator Fan Relay No. 2 and No. 3 Common Output
circuit from Radiator Fan Relay No. 3.
Is the resistance below 5.0 ohms?All
Ye s®Go To 22
No®Repair the Radiator Fan Relay No. 2 and No. 3 Common Output
circuit from Radiator Fan Relay No. 3 for an open.
Perform ROAD TEST VERIFICATION - VER-2.
22 Turn the ignition off.
Disconnect the Radiator Fan No. 1 harness connector.
Connect a fused jumper wire between the Radiator Fan No. 1 harness connector
cavities.
Turn the ignition on.
With the DRB, actuate the Low Speed Fan Relay.
Did Radiator Fan No. 2 activate on High speed?All
Ye s®Replace Radiator Fan No. 1.
Perform ROAD TEST VERIFICATION - VER-2.
No®Replace Radiator Fan No. 2.
Perform ROAD TEST VERIFICATION - VER-2.
23NOTE: Radiator Fan No. 2 is fed voltage from Radiator Fan Relay No. 3
during low speed operation and then fed voltage from Radiator Fan Relay
No. 2 during high speed operation by a common circuit connected to both
relays.
Turn the ignition off.
Disconnect the Radiator Fan Relay No. 2 harness connector.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the Radiator Fan No. 2 harness connector.
Measure the resistance between ground and the Radiator Fan Relay No. 2 and No. 3
Common Output circuit.
Is the resistance above 100k ohms?All
Ye s®Go To 24
No®Repair the Radiator Fan Relay No. 2 and No. 3 Common Output
circuit for a short to ground.
Perform ROAD TEST VERIFICATION - VER-2.
191
DRIVEABILITY - DIESEL
*CHECKING THE ELECTRIC RADIATOR FAN OPERATION ÐContinued

TEST ACTION APPLICABILITY
24 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the Radiator Fan No. 1 harness connector.
Using a 12-volt test light connected to 12-volts, check the Radiator Fan No. 1 Control
circuit.
Did the test light illuminate?All
Ye s®Repair the Radiator Fan No. 1 Control circuit for a short to
ground.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 25
25 If there are no possible causes remaining, view repair. All
Repair
Replace the Radiator Fan No. 2.
Perform ROAD TEST VERIFICATION - VER-2.
26 Turn the ignition off.
Disconnect the Radiator Fan Relay No. 3 harness connector.
Disconnect the Radiator Fan No. 1 harness connector.
Measure the voltage on the Radiator Fan No. 1 Control circuit.
Is the voltage above 1.0 volt?All
Ye s®Repair the Radiator Fan No. 1 Control circuit for a short to
voltage.
Perform ROAD TEST VERIFICATION - VER-2.
No®Go To 27
27 If there are no possible causes remaining, view repair. All
Repair
Replace Radiator Fan No. 1.
Perform ROAD TEST VERIFICATION - VER-2.
192
DRIVEABILITY - DIESEL
*CHECKING THE ELECTRIC RADIATOR FAN OPERATION ÐContinued

ENGINE CONTROL MODULE C1 (DIESEL) - BLACK 81 WAYCAV CIRCUIT FUNCTION
51 - -
52 K121 20DB BOOST PRESSURE SENSOR GROUND
53 - -
54 K957 20BK/OR MASS AIR FLOW SENSOR GROUND
55 N7 20DB/OR VEHICLE SPEED SENSOR SIGNAL
56 C918 20BK/LB A/C PRESSURE SENSOR GROUND
57 - -
58 K4 20BK/LB LOW IDLE POSITION SWITCH GROUND
59 - -
60 K9 20LB FUEL PRESSURE SENSOR 5 VOLT SUPPLY
61 K51 20BR/WT ECM/PCM RELAY CONTROL
62 - -
63 D21 20WT/BR SCI TRANSMIT
64 K151 20WT LOW IDLE POSITION SWITCH SENSE
65 - -
66 K936 20BR/YL ENGINE OIL PRESSURE SENSOR GROUND
67 - -
68 - -
69 C13 20LB/OR A/C COMPRESSOR CLUTCH RELAY CONTROL
70 N210 20DB/DG LOW SPEED RADIATOR FAN RELAY CONTROL
71 - -
72 N21 20DB/TN LIFT PUMP RELAY CONTROL
73 - -
74 T752 20DG/OR ENGINE STARTER MOTOR RELAY CONTROL
75 - -
76 - -
77 K152 20DB/WT GLOW PLUG RELAY CONTROL
78 N122 20DB/YL HIGH SPEED RADIATOR FAN DUAL RELAY CONTROL
79 - -
80 K87 20BR FUEL PRESSURE SOLENOID CONTROL
81 K87 20BR FUEL PRESSURE SOLENOID CONTROL
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CONNECTOR PINOUTS

A/C COMPRESSOR CLUTCH RELAYCAV CIRCUIT FUNCTION
30 INTERNAL FUSED B(+)
85 C13 18LB/OR (GAS) A/C COMPRESSOR CLUTCH RELAY CONTROL
85 C13 20LB/OR (DIESEL) A/C COMPRESSOR CLUTCH RELAY CONTROL
86 F202 18PK/GY (GAS) IGNITION SWITCH OUTPUT (RUN-START)
86 K342 16BR/WT (DIESEL) ECM/PCM RELAY OUTPUT
87 C3 18DB/YL A/C COMPRESSOR CLUTCH RELAY OUTPUT
87A --
ECM/PCM RELAY (DIESEL)CAV CIRCUIT FUNCTION
30 INTERNAL FUSED B(+)
85 K51 20BR/WT ECM/PCM RELAY CONTROL
86 INTERNAL FUSED B(+)
87 K342 16BR/WT ECM/PCM RELAY OUTPUT
87A --
FUEL HEATER RELAY (DIESEL)CAV CIRCUIT FUNCTION
30 INTERNAL FUSED B(+)
85 Z114 18BK/LG GROUND
86 INTERNAL IGNITION SWITCH OUTPUT (RUN-START)
87 N1 16DB/OR FUEL HEATER RELAY OUTPUT
87A --
LIFT PUMP RELAY (DIESEL)CAV CIRCUIT FUNCTION
30 INTERNAL FUSED B(+)
85 N21 20DB/TN LIFT PUMP RELAY CONTROL
86 F202 18PK/GY FUSED IGNITION SWITCH OUTPUT (RUN-START)
87 N2 18DB/YL LIFT PUMP RELAY OUTPUT
87A --
STARTER MOTOR RELAYCAV CIRCUIT FUNCTION
30 INTERNAL FUSED B(+)
85 T752 18DG/OR (GAS) ENGINE STARTER MOTOR RELAY CONTROL
85 T752 20DG/OR (DIESEL) ENGINE STARTER MOTOR RELAY CONTROL
86 INTERNAL IGNITION SWITCH OUTPUT (START)
87 T750 12YL/GY ENGINE STARTER MOTOR RELAY OUTPUT
87A --
RADIATOR FAN NO. 1 (DIESEL) - GRAY 2 WAYCAV CIRCUIT FUNCTION
1 N202 12DB/OR RADIATOR FAN NO. 1 CONTROL
2 N201 12DB/LG RADIATOR FAN RELAY NO. 1 OUTPUT
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CONNECTOR PINOUTS

RADIATOR FAN NO. 2 (DIESEL) - GRAY 2 WAYCAV CIRCUIT FUNCTION
1 Z823 12BK GROUND
2 N112 12DB/OR RADIATOR FAN RELAY NO. 2 AND NO. 3 COMMON OUTPUT
RADIATOR FAN RELAY NO. 1 (DIESEL) - BLUE 9 WAYCAV CIRCUIT FUNCTION
1- -
2 N201 12DB/LG RADIATOR FAN RELAY NO. 1 OUTPUT
3- -
4 K342 16BR/WT ECM/PCM RELAY OUTPUT
5- -
6 N210 18DB/DG LOW SPEED RADIATOR FAN RELAY CONTROL
7- -
8 A201 12RD/LG FUSED B(+)
9- -
RADIATOR FAN RELAY NO. 2 (DIESEL) - BLUE 9 WAYCAV CIRCUIT FUNCTION
1- -
2 N112 12DB/OR RADIATOR FAN RELAY NO. 2 AND NO. 3 COMMON OUTPUT
3- -
4 K342 16BR/WT ECM/PCM RELAY OUTPUT
5- -
6 N122 18DB/YL HIGH SPEED RADIATOR FAN DUAL RELAY CONTROL
7- -
8 A112 12OR/RD FUSED B(+)
9- -
RADIATOR FAN RELAY NO. 3 (DIESEL) - BLUE 9 WAYCAV CIRCUIT FUNCTION
1- -
2 Z823 12BK GROUND
3- -
4 K342 16BR/WT ECM/PCM RELAY OUTPUT
5 N112 12DB/OR RADIATOR FAN RELAY NO. 2 AND NO. 3 COMMON OUTPUT
6 N122 18DB/YL HIGH SPEED RADIATOR FAN DUAL RELAY CONTROL
7- -
8 N202 12DB/OR RADIATOR FAN NO. 1 CONTROL
9- -
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CONNECTOR PINOUTS