Leakyforlife
NAXJA Forum User
- Location
- GA
1991 laredo 4x4 4.0L. So my stock electric fan is not coming on and I've been checking everything! Tonight I went through the harness with my continuity meter and have some questions for all yall wiring and schematic gurus.
So the first thing I did was test the fan to make sure it was actually working. I bridged at the relay, pin 30 and 87 and the fan came on full power. I checked the resistance of the temp sensor in the thermostat housing at room temp and then with the jeep slightly warm. 8.8k ohm at around 80 degrees and 4.5k with engine warm but not hot. It is a brand new thermostat and the old thermostat at room air measured close at 8.9 ohms.
Next I traced the continuity of the temp sensor back to the main pins on the ECM and found it on the top row left side pin 2 and 4. I'm not sure of the exact pin out so I'm trying the describe what I'm seeing. I had continuity from the sensor wires to the ecm plug.
Then I traced pin 85 on the fan relay in the PDC to the ECM harness and found it on the middle row, right side as pin 1 from left to right with continuity.
The last pin I checked was the fan relay pin 86, which I assumed would be a ground for the relay coil. The interesting thing I found was that this pin goes with continuity to what I think is the chrystler OBD1 port near the ECM and nothing is plugged into it at that connector. The connector has six slots but only 4 terminals installed and a standard auto relay does not fit. One of the pins in this connector goes to ground.
To me it seems this is the missing connection (ungrounded coil from pin 86) and why my fan relay in the PDC is not energizing the coil to turn the fan on. But in my research the connector i am looking at is only for analyzing the ECM. Can anyone confirm this or help point me in the right direction to get my fan to come on when the temp is >218 or what ever the set point is.
I'm sure the engine in this 100 degree weather has gotten that high.
I also know it is somehow wired into the AC system and I do not have the AC compressor hooked up or the dryer for that matter. I have tested trying to get the fan on with the AC on but no luck.
So the first thing I did was test the fan to make sure it was actually working. I bridged at the relay, pin 30 and 87 and the fan came on full power. I checked the resistance of the temp sensor in the thermostat housing at room temp and then with the jeep slightly warm. 8.8k ohm at around 80 degrees and 4.5k with engine warm but not hot. It is a brand new thermostat and the old thermostat at room air measured close at 8.9 ohms.
Next I traced the continuity of the temp sensor back to the main pins on the ECM and found it on the top row left side pin 2 and 4. I'm not sure of the exact pin out so I'm trying the describe what I'm seeing. I had continuity from the sensor wires to the ecm plug.
Then I traced pin 85 on the fan relay in the PDC to the ECM harness and found it on the middle row, right side as pin 1 from left to right with continuity.
The last pin I checked was the fan relay pin 86, which I assumed would be a ground for the relay coil. The interesting thing I found was that this pin goes with continuity to what I think is the chrystler OBD1 port near the ECM and nothing is plugged into it at that connector. The connector has six slots but only 4 terminals installed and a standard auto relay does not fit. One of the pins in this connector goes to ground.
To me it seems this is the missing connection (ungrounded coil from pin 86) and why my fan relay in the PDC is not energizing the coil to turn the fan on. But in my research the connector i am looking at is only for analyzing the ECM. Can anyone confirm this or help point me in the right direction to get my fan to come on when the temp is >218 or what ever the set point is.
I'm sure the engine in this 100 degree weather has gotten that high.
I also know it is somehow wired into the AC system and I do not have the AC compressor hooked up or the dryer for that matter. I have tested trying to get the fan on with the AC on but no luck.