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Discussion Starter #21

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Discussion Starter #22
lol you all won't believe this...

Completely forgot there is a fuse in the cabin for the radiator fans.



The one on the right was that fuse, compared to a different 10A fuse on the left. The fuse is also noticeably "loose" like the contacts are loose. Not sure if that'll be the cause but it could be that simple.
 

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Any way of tightening up the fuse contact points? Maybe a small screwdriver and carefully tweaking the metal contacts by bending them a little? Could be the source of the intermittant problems.

Without looking at the wiring diagrams...I'd guess with that being a mini 10 amp fuse it's mainly for the relays and not the fan motors. You probably have a much larger fuse in the PDC under the hood for the motors.
 

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Discussion Starter #24
Any way of tightening up the fuse contact points? Maybe a small screwdriver and carefully tweaking the metal contacts by bending them a little? Could be the source of the intermittant problems.

Without looking at the wiring diagrams...I'd guess with that being a mini 10 amp fuse it's mainly for the relays and not the fan motors. You probably have a much larger fuse in the PDC under the hood for the motors.
I mean the fuse itself rattles. Maybe just separated from the plastic. The fuse under the hood in the power distribution box is a 40A and looks fine. I know it still doesn't explain why the fans would run seconds after starting the car then kick off.

Looking at how the PCM 60-way connector is oriented, a lot of the connections which could be related seem close to each other if I'm reading the diagram correctly:

 

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Good work! Guess you'll find out if any of that was the root cause of your issues.
 

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Discussion Starter #27
So are you thinking the disconnect is in the low speed fan circuit?
No clue. I'm just examining the pin locations on the 60-way connector to the PCM and all of the sensors required for fan operation seem to connect to pins within the same vicinity.

If it happens again, I'm going to use a DVOM and check the connector at the fan to see if it is getting power. If the fans turn off and power is still being sent, then perhaps the issue is within the RFI module. I'm not sure exactly what the RFI module consists of. If there is a switch in there or if it is just a junction for the fans. Maybe it overheats and shorts out.
 

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I think it would be helpful for you to sketch the entire radiator control circuit from the FSM - everything from the PCM fan control outputs, through the two fan control relays, to the fan motors. Unless you do that, I don’t see how you can troubleshoot it down to point of failure. And what I said in my earlier post may start making sense.
 

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Discussion Starter #29
Well, it happened again but I think I've made a little progress.

I was idling and a/c and fans turn off. Engine temp begins to rise so I shut the car off. But this time when I turn the car off and start it, I turn the a/c off and the fans keep running. I can't remember if I tried that the other day (could have swore I did) but the issue seems to lie with the a/c. So I tried again, started the car and kept the a/c on, fans turn off.

However, WHY would my fans stay off if my car is overheating? I wonder if a failing alternator could cause this. Going to test it.
 

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Why would the PCM turn off the fans is a more important question. The fans don't turn off and off by themselves.

If a PCM is cheap enough that would be my next route. After that you're looking at a possible wiring/connector problem. Again possible temperature related to break a connection somewhere.
 

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Discussion Starter #31
Why would the PCM turn off the fans is a more important question. The fans don't turn off and off by themselves.

If a PCM is cheap enough that would be my next route. After that you're looking at a possible wiring/connector problem. Again possible temperature related to break a connection somewhere.
So yeah, I agree it seems to be the PCM.

Today I drove without touching the a/c. It was fine through highway and some lights until I turned the car off. Turned it back on and didn't drive one block before I clearly noticed a change. Even my transmission was shifting weird a couple of times. At a stop, if my car was in gear, it would jolt forward slightly shortly after stopping.

Going to order a PCM and hope it fixes it. Otherwise it could be a ground issue.
 

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So yeah, I agree it seems to be the PCM.

Today I drove without touching the a/c. It was fine through highway and some lights until I turned the car off. Turned it back on and didn't drive one block before I clearly noticed a change. Even my transmission was shifting weird a couple of times. At a stop, if my car was in gear, it would jolt forward slightly shortly after stopping.

Going to order a PCM and hope it fixes it. Otherwise it could be a ground issue.
Have you verified the engine temp? As in a thermal gun pointed at the thermostat housing? All LHs have differen't points on the gauge they operate at. A new sensor can change it.


Also, that surge forward may be it shifting into 1st. What other changes did you see?
 

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Discussion Starter #33 (Edited)
The engine temp and sensor are good.

I disconnected the battery for a few hours yesterday and I'll drive it tomorrow to see how it runs.

The tranny issue is what convinced me of the PCM. Before the cooling fan issue manifests itself, the car shifts perfect with no issues. Once the car has warmed up and has been driving awhile, and usually after turning it off and starting again, it's as if the PCM gets 'confused' for some reason and cuts off the cooling fans. At the same time, the shifting is noticeably different. Around 5 seconds or so after stopping, sometimes the transmission feels like it wants to go into gear, only does it once until I go and stop again.

But those are the only symptoms of the issue. All of the gauges look fine. The coolant gauge behaves normally. A/C works just fine until the fans cut off. Refrigerant pressure is good. No CEL or codes.

I've contacted a few shops from car-parts and haven't gotten a quote yet for a PCM.

I also thought about just eating the diagnostic fee at the dealer since they have the DRB III scanner they could probably tell me immediately what is wrong. But their fee is 3x the price of a used bone yard PCM, figure I'll try it first.
 

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The engine temp and sensor are good.

I disconnected the battery for a few hours yesterday and I'll drive it tomorrow to see how it runs.

The tranny issue is what convinced me of the PCM. Before the cooling fan issue manifests itself, the car shifts perfect with no issues. Once the car has warmed up and has been driving awhile, and usually after turning it off and starting again, it's as if the PCM gets 'confused' for some reason and cuts off the cooling fans. At the same time, the shifting is noticeably different. Around 5 seconds or so after stopping, sometimes the transmission feels like it wants to go into gear, only does it once until I go and stop again.

But those are the only symptoms of the issue. All of the gauges look fine. The coolant gauge behaves normally. A/C works just fine until the fans cut off. Refrigerant pressure is good. No CEL or codes.

I've contacted a few shops from car-parts and haven't gotten a quote yet for a PCM.

I also thought about just eating the diagnostic fee at the dealer since they have the DRB III scanner they could probably tell me immediately what is wrong. But their fee is 3x the price of a used bone yard PCM, figure I'll try it first.

Of course the Transmission act different once warm. Fluid viscosity changes. The TCM will change shifting with fluid temp. If you unhooked battery then you reset the adaptive learning for the transmission. Drive it normally for 100 or so miles as it reads into your driving style.


I did not ask about rather the gauge works. I asked have you verified the overheating issue? Also, a/c transducer can cause several fan issues although most the time it cuts them on. or keeps a/c from turning on. I suggest re looking at it cause if it fails the system will turn fans off ad a/c system off. The factory sensor is no longer easily found so I always grabb a few junkyard ones. Or you have to re wire a new connector for the replacement.

PCM does not control shifting. TCM does. TCM does talk to PCM but ultimately TCM decided shifting not PCM.
 

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Discussion Starter #35
Of course the Transmission act different once warm. Fluid viscosity changes. The TCM will change shifting with fluid temp. If you unhooked battery then you reset the adaptive learning for the transmission. Drive it normally for 100 or so miles as it reads into your driving style.


I did not ask about rather the gauge works. I asked have you verified the overheating issue? Also, a/c transducer can cause several fan issues although most the time it cuts them on. or keeps a/c from turning on. I suggest re looking at it cause if it fails the system will turn fans off ad a/c system off. The factory sensor is no longer easily found so I always grabb a few junkyard ones. Or you have to re wire a new connector for the replacement.

PCM does not control shifting. TCM does. TCM does talk to PCM but ultimately TCM decided shifting not PCM.
The engine coolant temperature sensor provides an input to the Powertrain Control Module (PCM) on circuit K2. This sensor input is also used for the instrument cluster coolant temperature gauge. See: Instrument Panel, Gauges and Warning Indicators\Temperature Gauge\Description and Operation
If the gauge is reading/behaving normally, then it is giving good info to the PCM. They are on the same circuit. The coolant temp sensor is new and has operated fine since I installed it. I have no reason to believe it is faulty. So yes, overheating is confirmed. When fans turn off, engine temp begins to heat up beyond 220* C. Fans do not come on until I turn off vehicle and restart with A/C off.

The A/C pressure transducer could very well be faulty. If so, the compressor would turn off and fans would turn off... IF my engine temp was below the threshold for the PCM to keep them on. When engine heats up, PCM should ground the fans. But it doesn't... until I restart the vehicle then fans stay on until engine reaches normal temperature. I don't believe transducer is faulty either as a/c performs perfectly. The PCM only receives signals from those two sensors, which are working fine, to run the cooling fans, thus PCM is suspect.

The TCM relies on data from the PCM also. A faulty PCM can definitely alter shifting of the transmission based on that data if it is bad. Which only happens during this period of odd behavior. So unless the TCM can control the cooling fans (can't) then the PCM is still the common denominator. Won't know for sure until I get one... don't know why these shops aren't calling me back.
 

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Discussion Starter #36
Did it again today... this is honestly the weirdest thing I've ever experienced in a car. You can damn near time it to your watch when it will happen if you drive the same route. Within a mile every time.

Today I had the heat on the whole time. Driving to my destination was fine, temp didn't get higher than 1/3 and tranny shifted great, quick and firm, but smooth shifts. Coming back is when it happens and sure enough. Only this time while sitting at a light, instead of the transmission trying to go in gear, my brake pedal sinks about an inch, the idle changes a bit then everything is normal. Transmission shifts noticeably different after this point as well as the cooling fans being off.

Weirdest ****ing thing I've ever seen by far. Just hope it really is the PCM and my entire car isn't falling apart all at once. So when the PCM gets here I'll update more.
 

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Discussion Starter #37
I think I am on to something now.

I've been probing away with the DVOM and I get a 5V reference at the A/C transducer, but that 5V reference shorts out very easily. Moving the connector slightly drops it to 0V. It shares that 5V reference with the MAP and TPS. It also shares a ground connection with the air temperature sensor, coolant temperature sensor and crank position sensor.

My A/C transducer connector also looks different from the one in the wiring diagram. Mine has 4 round terminals with 3 wires. I put my DVOM leads on to the TPS to monitor it's 5V signal and messed with the A/C transducer to see if it screws with the signal but it did not seem to.

Question is now, could this explain my symptoms if the issue manifests only when engine is warm regardless of A/C on or off? Could the 5V signal shorting out screw with the grounds on that circuit listed above?

I'll know more tomorrow when I drive it around without the transducer plugged in.
 

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Discussion Starter #38
I think we have success.

Driving today without transducer connected did not manifest any symptoms. Transmission shifts fine, radiator fans were working throughout drive.

I'm guessing the transducer is shorting out inside at a certain temperature.
 

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See post #4! I told ya!
 
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