Im working on a friend of mines van. The cooling fans will work sometimes and sometimes they wont. I jumped the fan motors with a jumper wire and both run when jumped. The fuse is good. I checked the two plugs that plug into the motors and both prongs on both plugs are grounded. One should be hot and the other grounded. However, like i said, both are grounded. I am thinking i need a cooling fan relay? Anyone else dealt with this? I hate to spend a hundred bucks and that not be the problem. Thanks for any help.

 

I use an drb3 to actuate the fans. If they come on the relay in most cases is good. You may want to look at the temp sensor or wiring. Do you have a ck engine lite on?

 

Check engine light was on. However, we live about 30 minutes from anywhere that can read the code. The tempature gauge is working. The reason i suspect the relay is because both prongs on the plugs are grounded. Even if the tempature sensor was bad shouldnt one of the fans come on when the ac is turned on?

 

Depends on the year of the van, 1996 to 2000 is on the frame rail under the air filter box.2001 to 2007 is in the front bumper on the passenger side.

 

I know where the relay is. But doesnt both prongs on both connectors being grounded sound like a stuck relay? Is there anyway to test the relay?

 

Not really. plug in a known good relay and recheck.

 

RADIATOR FAN RELAY
DESCRIPTION
The radiator fan relay is a solid state type and is located under the left front headlamp module Radiator Fan Relay Refer to WIRING DIAGRAMS for a circuit schematic.

OPERATION
The solid state radiator fan relay is controlled by the Powertrain Control Module (PCM) by way of a Pulse Width Modulated (PWM) signal. The relay control circuit supplies a 12 volt signal to the PCM. The PCM then pulses the ground circuit to achieve fan on time. The relay provides a voltage to the fan motors which is proportional to the pulse width it receives from the PCM. The duty cycle ranges from 30% for low speed operation, then ramps-up to 100% for high speed operation. This fan control system provides infinitely variable fan speeds, allowing for improved fan noise, A/C performance, better engine cooling, and additional vehicle power.

To control operation of the relay, the PCM looks at inputs from:

•Engine coolant temperature
•A/C pressure transducer
•Ambient temperature from the body controller
•Vehicle speed
•Transmission oil temperature
The PCM uses these inputs to determine when the fan should operate and at what speed. Refer to Specifications - Radiator Fan Operation in this section.

 

OPERATION
The solid state radiator fan relay is controlled by the Powertrain Control Module (PCM) by way of a Pulse Width Modulated (PWM) signal. The relay control circuit supplies a 12 volt signal to the PCM. The PCM then pulses the ground circuit to achieve fan on time. The relay provides a voltage to the fan motors which is proportional to the pulse width it receives from the PCM. The duty cycle ranges from 30% for low speed operation, then ramps-up to 100% for high speed operation. This fan control system provides infinitely variable fan speeds, allowing for improved fan noise, A/C performance, better engine cooling, and additional vehicle power.

To control operation of the relay, the PCM looks at inputs from:

Engine coolant temperature
A/C pressure transducer
Ambient temperature from the body controller
Vehicle speed
Transmission oil temperature
The PCM uses these inputs to determine when the fan should operate and at what speed.

This is for the 2001 thru 2007.

 

Hi, I'm new to this forum and have a question about the PWM Relay function.
I recently replaced the PWM relay on my 2002 jeep grand cherokee and it worked fine for a few days, then it stopped working. I bought a replacement from Rock Auto parts and it came with a new connector. I replaced the relay and connector. I also cleaned the metal surface where it mounts and applied white thermal grease. I checked the Fan to see it it turned freely and checked the operating current draw and it was ~25 amps, when connected directly to the battery. I wonder if one of the crimped wires came loose (need to check). Now for the question: What is the voltage level and frequency/pulse width of the signals that are sent to the PWM relay to control the fan? Does anyone have a schematic of the relay itself? I'm thinking or replacing it with a more robust relay.
Thanks,
Matt