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Donny
Donny, Shop Foreman
Category: Jeep
Satisfied Customers: 828
Experience:  A.S.E. Certified A1-A8,L1,X1,T1,T2 Over 25 years Experience with Chrysler - Dodge - Jeep
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p1491 code on a 1999 jeep cherokee. replaced relay and still

Customer Question

p1491 code on a 1999 jeep cherokee. replaced relay and still have the code
Submitted: 7 years ago.
Category: Jeep
Expert:  Donny replied 7 years ago.

Hello

 

When Monitored and Set Condition:

P1491-RAD FAN CONTROL RELAY CIRCUIT

When Monitored: With the ignition key on, battery voltage greater than 10.0 volts and

the PCM requests the radiator fan to be turned on.

Set Condition: An open or shorted circuit is detected in the radiator fan relay control

circuit.

 

POSSIBLE CAUSES

RADIATOR FAN CTRL RLY CIRCUIT WIRE HARN INTERMITTENT DEFECT

RADIATOR FAN CTRL RLY CIRCUIT WIRE HARN OBSERVABLE DEFECT

RADIATOR FAN RELAY GROUND CIRCUIT OPEN

RAD FAN RELAY CONTROL CIRCUIT OPEN

RADIATOR FAN RELAY CONTROL CIRCUIT SHORT TO GROUND

RAD FAN CONTROL RELAY DEFECTIVE

PCM DEFECTIVE

 

Ignition On, Engine Not Running

With the Scan tool, actuate the Radiator Fan Control.

Does the Radiator Fan Motor Cycle on and off?

Yes Go To 641

No Go To 643

 

641

Ignition On, Engine Not Running

With the DRB, actuate the Radiator Fan Control.

Wiggle the Wiring Harness from the Relay to the Powertrain Control Module.

Did the wiggling interrupt the Radiator Fan Motor cycling?

Yes Repair as necessary where wiggling caused the cycling to be

interrupted.

No Go To 642

 

642

Turn ignition off.

inspect the Wiring and Connectors.

Were any problems found?

Yes Repair as necessary.

No Test Complete.

 

643

Turn ignition off.

Disconnect the Radiator Fan Relay.

Using an ohmmeter, measure the Radiator Fan Relay Ground Circuit to Ground.

Is the resistance below 5.0 ohms?

Yes Go To 644

No Repair the open Ground Circuit.

 

644

Turn ignition off.

Disconnect the PCM Connector.

Note: Check connectors - Clean/repair as necessary.

 

Disconnect the Radiator Fan Relay Connector.

Note: Check connectors - Clean/repair as necessary.

 

Using an Ohmmeter, measure the resistance of the Rad Fan Relay Control Circuit

from the Relay to the PCM.

Is the resistance below 5.0 ohms?

Yes Go To 645

No Repair the open Radiator Fan Relay Control Circuit.

 

645

Turn ignition off.

Disconnect the Radiator Fan Relay Connector.

Note: Check connectors - Clean/repair as necessary.

Disconnect the PCM Connector.

Using an Ohmmeter, measure the Radiator Fan Relay Control Circuit to ground.

Is the resistance below 5.0 ohms?

Yes Repair the Radiator Fan Relay Control Circuit for a short to

ground.

No Go To 646

 

646

Turn ignition off.

Disconnect the PCM Connector.

Note: Check connectors - Clean/repair as necessary.

 

Connect a jumper wire to the Radiator Fan Relay Control Circuit at PCM.

Momentarily connect the other end of the jumper wire to a good ground.

Did the Radiator Fan actuate?

Yes Replace the Radiator Fan Relay.

No Go To 647

 

647

If there are no other potential causes remaining, the PCM is assumed to be defective.

View repair options.

Repair

Replace the PCM.

 

I hope that this helps you

 

Thank you

 

Donny

 

RADIATOR FAN RELAY - 4 WAY
CAVCIRCUITFUNCTION
10BKGROUND
2DB/BKRADIATOR FAN RELAY CONTROL
3DGRADIATOR FAN RELAY OUTPUT
4GYFUSED B(+)

 

POWERTRAIN CONTROL MODULE C2 - WHITE 32 WAY
CAVCIRCUITFUNCTION
1VT (4.0L)TRANSMISSION TEMPERATURE SENSOR SIGNAL
2DB/TN (4.7L)FUEL INJECTOR NO. 7 DRIVER
3--
4WT/DBFUEL INJECTOR NO. 2 DRIVER
5YL/WTFUEL INJECTOR NO. 3 DRIVER
6GYFUEL INJECTOR NO. 5 DRIVER
7BR (4.7L)COIL DRIVER NO. 7
8PK (4.0L)GOVERNOR PRESSURE SOLENOID CONTROL
9TN/PK (4.7L)IGNITION COIL DRIVER NO. 2
9TN/PK (4.0L)IGNITION COIL DRIVER NO. 2
10DGGENERATOR FIELD DRIVER
11DG/LB (4.0L)TORQUE CONVERTER CLUTCH SOLENOID CONTROL
12BR/DBFUEL INJECTOR NO. 6 DRIVER
13DG/GY (4.7L)FUEL INJECTOR NO. 8 DRIVER
14--
15TNFUEL INJECTOR NO. 2 DRIVER
16LB/BRFUEL INJECTOR NO. 4 DRIVER
17DB/PKRADIATOR FAN RELAY CONTROL
18--
19--
20--
21BR/WT (4.0L)3-4 SHIFT SOLENOID CONTROL
22--
23GY/YLENGINE OIL PRESSURE SENSOR SIGNAL
24--
25DB/BK (4.0L)SPEED SENSOR GROUND
26--
27WT/ORVEHICLE SPEED SENSOR SIGNAL
28LG/WTOUTPUT SPEED SENSOR SIGNAL
29LG/RDGOVERNOR PRESSURE SENSOR SIGNAL
30PK/YL (4.0L)TRANSMISSION CONTROL RELAY CONTROL
31VT/WT5V SUPPLY
32--