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Discussion Starter #1
Daughter's 93 Lebaron...I wanted to check the timing this morning as part of addressing a slightly high idle speed issue, so I idled the car, hooked up timing light and unplugged the CTS. Set the timing, then I saw the coolant overflow bottle gurgling. Car was overheating, and I had failed to notice that the electric fan did not kick on when I unplugged the CTS.

I straight wired the fan and it tests good.

I checked for key-on power to the underhood fan relay, and I have power.

Swapped relays, with no success.

Also checked and verified power at the large colored fuse for the fan underhood.

Swapped fuses, no success.

Checked for power to the green wire at the fan connector, and NO power. Of course, there is also no power in the positive terminal of the fan connector.

Any ideas? Car has never overheated before. Could this be a CTS problem?
 

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Does the radiator fan come on with the A/C on? Did you disconnect the correct 2-wire sensor to check timing?
The single violet wire coolant sensor is only for the dash gauge.
Did the 'ck eng' light come on when you disconnected the sensor and is it still on? There may be a stored CTS fault code.
 

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Discussion Starter #3
A/C not in car yet...I definitely disconnected the correct sensor, in the driver side of the therm housing. I have also determined that fan will come on when I put a jumper wire across the terminals in the relay block. When I insert the relay, the fan "bumps" for a second, but will not come on. Same situation with 2 different relays. Are both relays bad?

I am getting a code 35 for circuit issue with rad fan.
 

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There should be power on 2 of the terminals of the fan relay with the key in run. One is for the relay coil and the other is the "source" power to the fan.

The engine controller applies a ground to the other side of the relay coil when the engine controller (ECM) receives information that the fan should kick on (or relay should close). Then the relay "switch" or contact should close and apply the source power to the fan.

The relay switch contacts are numbered 30 and 87, so a jumper across the socket contacts that correspond to 30 &87 will turn the fan on if you have source power.

Here is a picture:
 

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Discussion Starter #5
thanks John, yes I have power to two sockets and the fan comes on with a jumper wire in place of the relay. i have now tried 3 relays, two of which are known good ones. I note that I do NOT have power in the light green wire going to the relay box from the dash with key on. Could this mean a wiring issue under the dash? As a side note, the ignition switch, or lock cylinder has been acting up on it...
 

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With power to both contacts, the only thing left is that the computer is not applying a ground to close the coil circuit. That could mean a wiring problem or a faulty computer. My guess would be a wiring problem... and possibly a dirty pin or socket on the computer connector.

Try this test: With the engine coolant sensor unplugged, ignition switch in run, loosen the computer plug retaining screw and try wiggling the computer connector to see if the fan "bumps" or starts. If necessary, remove the plug (turn the ignition switch off) and spray contact cleaner on the pins and sockets. Inspect all pins for corrosion. Carefully insert and remove the plug a few times to sweep the contacts clean. That might take care of it.
 

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Discussion Starter #7
Will do. I did disconnect the computer connector earlier and saw a bit of corrosion on a few terminals. I sprayed them with contact cleaner, but I need to devise a better tool for cleaning down in the connector better. I can also try the computer out of my Daytona to rule that out.

I'll update tomorrow night. Thanks..
 

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It looks like pin (cavity) 31 of the SBEC connector is the fan relay control. Inspect that pin. If it is possible to make a test jumper to ground the wiring harness pin 31 with the fan ready to kick on, you can test the integrity of the wiring back to the relay. If the fan runs you know the wiring is good up to the computer. See the minimopar.net resource for the SBEC pinouts here:

http://minimopar.knizefamily.net/ecu/sbec-1990-tbi.html
 

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Discussion Starter #9
Before reading your last post, I swapped computers with my Daytona. I also wiggled the connector and all wiring in the area while key was on, all with no success. Need to eat now, and will get on it again tom night. Thanks!
 

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Update:
I used a test light to ground pin number 31, and the fan did come on. I redid the ground wire running from the O2 sensor to the driver side rear of the block, but no success. This ground was hanging by a thread though, so it needed to be replaced anyway.

I then found that the ground strap at the pass side firewall that runs to the intake had broken at the intake end. Tried to find a spare in the shop, could not. Will buy one from the Help section at AZ tomorrow, and I HOPE this fixes it!
 

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That ground strap is vital, will help if not solve the problem.
 

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Discussion Starter #12
That ground strap is vital, will help if not solve the problem.
Put new ground strap on, and no change. I was hoping that was the problem.

Just to make sure....with key on and CTS unplugged, fan should be running, correct?

If so, I just tested this with my Daytona, which has no issues, and fan does not come on with key on and CTS unplugged on it either.
 

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You are sure that you had the key all the way to run? How about when it is running? I've always had the fan come on when I pulled the CTS to set the ignition timing. I hope we aren't chasing our tail here. :frusty:
 

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That's how it works, Russ. Since you jumpered the load side of the relay socket and it turned on, the harness from the relay to the fan must be good. The negative coil side is not switching to ground, from what you said. In that case, it's either the computer, a bad connection at the computer, or a bad connection between computer and the relay socket. First and easiest thing to check is the connectors, then the wiring.
 

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Discussion Starter #15
Just tested the Daytona again, and fan does not come on with key on and cts unplugged. It does come on with engine running, however. On the LeBaron, I tried running it earlier also, and still no fan on.
You are sure that you had the key all the way to run? How about when it is running? I've always had the fan come on when I pulled the CTS to set the ignition timing. I hope we aren't chasing our tail here. :frusty:
 

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Discussion Starter #16
Could this be an ignition switch issue? We have had intermittent trouble getting the key out of the switch. Many times, it will not fully reach the off position, in which the key can be removed. From my study of the wiring diagram in the FSM, a dark blue wire runs from the ignition switch to one side of the fan relay.

This would explain a bad connection between the computer and the relay.I ruled out the computer a couple of days ago, when I installed the one from the Daytona (assuming the 1990 and 93's are the same).
 

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If the switch were not operating properly, it would either keep 12V on, or off. If it were on, the fan could run with the key off. If it were off, the computer and the fan relay would get no 12V. So I don't think that's what's happening here.
 

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Since you measured 12 volts at the relay socket for both the source power and the coil power... and when you ground pin 31 of the SBEC the fan comes on, I would have to say this is not likely an ignition switch issue unless there is some very intermittant situation that occurs when you are testing.

Base on the above observation, I think we can safely say that the relay is good and the wiring from pin 31 to the PDC relay socket is good. Since the fan also runs when pin 31 is grounded, we know the wiring to the fan and the fan motor is good. Swapping computers (assuming they are compatable) did nothing... but did you actually try it (disconnecting CTS) with the engine running? (now that we established that the engine must be running and CTS disconnected to force the fan on).

Other than a bad SBEC wiring harness connector or some unlikely wiring issue from the CTS, the only thing left is the CTS.

You may want to repeat the tests with the 2nd computer and the engine running just to double check.

In one post, you mentioned that the fan "bumped" (like it was trying to start) when you were replacing a relay. There may be a clue there, but no light bulb is coming on in my brain :) other than something seems intermittant.
 

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I use DeOxit D100 on real head scratcher's like this. It's the only contact cleaner that seems to do anything. The "bumping the relay and have things work for a second" sounds mighty suspicious. My little '95 Spirit ECU did the same thing - I've got continuity and function all the way to the ECU, but the ECU refuses to do anything with it. Tired of fooling around so I put a high amp thermostatic switch in a replacement thermostat housing, and fed a relay coil with ignition voltage (grounds through the thermostatic switch). 80ma draw through the relay coil and 25 amps capacity of the switch -- it ought to last for awhile. I had to learn the hard way about Tyco relays versus all the look-alikes.
 

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It can't be the CTS, because once you unplug it, it's irrelevant whether it's bad or not. The computer is supposed to switch the fan relay on when the CTS is open-circuited. Unplugging it guarantees an open circuit.
 
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