BCarter
Junior Member
All, I have a 2003 2500 with the 5.7 and the condenser fan will not run with the A/C on as it should. Additionally, I'm getting a Check Engine Light with a P0408 Condenser Fan Relay Circuit Error. Here is what I've done so far:
1) Confirmed the fan itself works, applied 12 volts to the connector and it works.
2) Checked the fuse, verified continuity across the fuse.
3) Bench tested the relay which passed. Confirmed continuity across 30 and 87A when disengaged, applied power across 85/86, heard the click and confirmed continuity across 30/87.
4) Confirmed fuse 12 and 27 were good from the diagram below and continuity between 85/30 to fuse 12.
5) No voltage to the fan connector, but getting ground.
Here is where I am and need some help.
I have the condenser fan circuit diagram, attached. From what I understand pin 85 should receive power and pin 86 should receive ground from the PCM engaging the relay. Pin 85 is getting power, but pin 86 does NOT have continuity to ground when the A/C is on and I believe it should.
If my understanding is correct, what else in the circuit would stop the ground from coming to 85 from the PCM, what would be the next test steps or am I misunderstanding the functionality? How would this coincidence with no voltage at the connector, but a good ground per number 5 above?
Side note, this is a new truck to me. I was also having issues with the AC blower fan staying on after turning the truck off, a new ignition switch resolved this. I'm also having issues with the wipers coming on as soon as the key is turned on even though the switch is off, they stop when cycling on/off a few seconds later. I suspect this will be resolved with a new wiper switch which I'm waiting to receive, but figured it was worth mentioning in case they may be related in anyway. The ignition switch did have noticeable dark burn like marking around one of the pins almost like there has been some electrical arcs.
Appreciate any and help on this!
1) Confirmed the fan itself works, applied 12 volts to the connector and it works.
2) Checked the fuse, verified continuity across the fuse.
3) Bench tested the relay which passed. Confirmed continuity across 30 and 87A when disengaged, applied power across 85/86, heard the click and confirmed continuity across 30/87.
4) Confirmed fuse 12 and 27 were good from the diagram below and continuity between 85/30 to fuse 12.
5) No voltage to the fan connector, but getting ground.
Here is where I am and need some help.
I have the condenser fan circuit diagram, attached. From what I understand pin 85 should receive power and pin 86 should receive ground from the PCM engaging the relay. Pin 85 is getting power, but pin 86 does NOT have continuity to ground when the A/C is on and I believe it should.
If my understanding is correct, what else in the circuit would stop the ground from coming to 85 from the PCM, what would be the next test steps or am I misunderstanding the functionality? How would this coincidence with no voltage at the connector, but a good ground per number 5 above?
Side note, this is a new truck to me. I was also having issues with the AC blower fan staying on after turning the truck off, a new ignition switch resolved this. I'm also having issues with the wipers coming on as soon as the key is turned on even though the switch is off, they stop when cycling on/off a few seconds later. I suspect this will be resolved with a new wiper switch which I'm waiting to receive, but figured it was worth mentioning in case they may be related in anyway. The ignition switch did have noticeable dark burn like marking around one of the pins almost like there has been some electrical arcs.
Appreciate any and help on this!
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