Just Expect Electrical Problems

Discussion in 'Technical' started by disord3r, Aug 21, 2012.

  1. Today my Jeep didn't start. I last drove it on Saturday. Nothing I could find was "on" that might have drained the battery. Jumped it, it started pretty quickly, and then that was that. I drove it around to run errands and it started up every time I needed it to. 14v when running, 12v when key is on but the engine is off.

    While I was out, I happened to look down and notice the engine temp WAY above where it should normally be. I drove more, it went down, I stopped at lights and it crept back up. Eventually it got high enough that the "check gauges" light came on, so I just went home on a route that had no traffic to keep things cool.

    At home with the key in the ignition and in the on position, the electric fan should have been running to cool the engine, but it wasn't. I could spin the fan freely, but it made no attempt to run on its own. I need to get my multimeter out and try to figure it out, so I'm assuming if I disconnect the plug closest to the fan and put the probes in, I should see a high(er) voltage when it's above temp and the fan should be running, and the voltage would go low when the engine gets back down to normal temps. That would tell me it's a bad fan motor. If it's consistently low, even when the temp is up and the fan should be running, then it should be a fuse or relay or whatever. Does that all sound right?

    Also, what could the flat battery situation have to do with the fan? Not related at all?
  2. Reading more about it...

    I have an engine coolant level sensor in the fill bottle somewhere. That should be unrelated here, but would warn of a low coolant level. I also have an engine coolant temperature sensor on the thermostat housing that sends the temp reading to the PCM to display the reading on the dash gauge. The dash guage works as it should, so that's also fine.

    My guess is that the ECT sensor reading is also sent to the fan in some way. I have a 40A fuse in the distribution block that LOOKS fine, but I'll get another one for a test swap. I also have a relay under the headlight (ugh). There may or may not be a fan controller of some kind. So those are three things I can check, apart from the fan motor itself.

    This is a 2002 Jeep Grand Cherokee, BTW.
  3. Yeah, you bought a Grand Cherokee. That's the main problem.
  4. Its usually the ect sensor, motors rarely go bad unless the car is very old.
  5. #5 disord3r, Aug 22, 2012
    Last edited by a moderator: Apr 25, 2016
    From what I was reading though, if the ECT wasn't working, the temp gauge in the dash would be dead or min or max. It behaves exactly as I would expect based on the amount of airflow into the grill, so I'm pretty sure the ECT is good. Coincidentally, the fan motor used in the GC electric fans is generally thought to be weak and shitty, so I don't mind trying to finesse a new one in there, or this: http://www.jeepsunlimited.com/forums/showthread.php?t=496635

    I was just mainly wondering about my logic regarding voltage at the fan connector.
  6. Run your own wires to the fan from the battery to see if it is dead or it is a electrical gremlin.
  7. I did the mechanical fan until I can figure out what I want to do about the electric. All and all it was pretty easy to add, but the space was super tight to it took me as long to install as it did to actually acquire and assemble the parts.
  8. Just checked on RockAuto, the radiator fan relay is the same shitty one they also used in Chrysler/Dodge minivans which is the primary cause for radiator fan issues.

    They had issues with wiring harnesses also melting/damaged with this particular relay. Dorman makes a repair kit with a better designed relay and a new connector with pigtail.

    I do agree with the ECT suggestion too. ECTs will fail more often due to lack of cooling system maintenance, rust/scale and higher water content will corrode the tip of the sensor, which will mess with the signal it sends back to the ECU. Dashboard temp gauges have large dead spots, this started with most manufacturers back in the late 80s to reduce the amount of unnecessary warranty work. Basically customers would come back in droves complaining that they don't remember the needle being at a certain point.

  9. Like I said, my dash gauge works perfectly, but if replacing the ECT would fix it, I'm willing to gamble. It's right there on the thermostat housing and is super easy to get to compared to the relay under the headlight. I'm just not looking forward to splicing/soldering wiring.
  10. This is such an easy fix. Just plug the radiator fan in a way that as soon as you turn the ignition, the fan goes on, all the time.

    That's what I did to my super duper 1999 Saturn SL. It had the same problem, so instead of looking / finding / testing some electrical nightmare, I plugged it direct on the ignition.

    Taddam! fan always on and no worries about an overheating engine.
  11. now my window broke lol

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