dssenne Posted May 29, 2015 Share Posted May 29, 2015 Any help would be greatly appreciated! The main cooling fan has stopped working on my '92 legacy. If I jump the Pressure Switch (Trinary) as shown below, the fan WILL come on. If I jump the Main fan relay under the hood (below), the fan will also work. But without jumping either one of these, nothing. I replaced the thermostat and the coolant temperature sensor with no results. The fuses for the fan are not blown. I've swapped out the other three A/C relays into the #2 spot just as a test, but that made no difference The A/C compressor and fan are also not working, but my concern right now is just getting the car to be drivable. It seems like the main fan should be able to work regardless whether the A/C is working or not. Does anyone have any ideas where I should look next? I'm at a loss! Link to comment Share on other sites More sharing options...
lmdew Posted May 30, 2015 Share Posted May 30, 2015 Is the temp gauge getting above the 1/2 way mark? The fans are independent and 2 speed on one or both. If the engine is hot a single fans comes on, if you have the AC on, both fans should come on. Is your AC Charge low? Link to comment Share on other sites More sharing options...
Cougar Posted May 30, 2015 Share Posted May 30, 2015 I suggest you see if the fans will turn on by using the TEST connectors, which are under the dash I believe. By plugging them together it will start the TEST mode. If the fan doesn't turn on that way then I suspect the trouble is with the ECU control for the fan. The ECU makes a ground connection to activate the fan relay coil which ties power to the fan motor. Another way to prove it is to manually ground the relay coil lead going to the ECU. Some folks have had this same issue. The lead ties to a driver IC inside the ECU which can be replaced if you are into that kind of repair. 1 Link to comment Share on other sites More sharing options...
dssenne Posted May 30, 2015 Author Share Posted May 30, 2015 Is the temp gauge getting above the 1/2 way mark? The fans are independent and 2 speed on one or both. If the engine is hot a single fans comes on, if you have the AC on, both fans should come on. Is your AC Charge low? Yes, the gauge does go above 1/2 way. If I switch on the AC, the compressor doesn't kick in and the AC fan doesn't come on. Just using a cheap-o gauge that comes with a can of R134, the pressure was high on the Low port. Shouldn't the main cooling fan work even if the AC doesn't? Link to comment Share on other sites More sharing options...
dssenne Posted May 30, 2015 Author Share Posted May 30, 2015 I suggest you see if the fans will turn on by using the TEST connectors, which are under the dash I believe. By plugging them together it will start the TEST mode. If the fan doesn't turn on that way then I suspect the trouble is with the ECU control for the fan. The ECU makes a ground connection to activate the fan relay coil which ties power to the fan motor. Another way to prove it is to manually ground the relay coil lead going to the ECU. Some folks have had this same issue. The lead ties to a driver IC inside the ECU which can be replaced if you are into that kind of repair. I just went out and tried connecting both the green and black connectors, but nothing changed. Replacing IC's sounds a bit beyond me. I know this would be lame, but since this is an old car with lots of miles and a few other problems (we really only use it around town and as a backup), would it hurt anything if I just jumped the pressure switch so that the fan was on whenever it was running and just lived without AC? Link to comment Share on other sites More sharing options...
Cougar Posted May 30, 2015 Share Posted May 30, 2015 It is strange that nothing happened when you connected both sets of connectors. I would check for a power problem going to the ECU to make sure that is okay and if that was good I would have to suspect the ECU has a problem. To test the Main Fan operation you could try grounding the lead going to the ECU that controls the Main Fan operation. The fan should turn on if everything else with the circuit is okay. From what you say about the low pressure side of the AC system it seems that the system may be over charged. I would have a AC shop take a look at things. I don't recommend bypassing the pressure switch. I am a bit confused with a statement you made in post 4. You seem to indicate that the Main Fan turns on when the engine gets to hot but then other statements seem to indicate neither fan works. Can you clarify that for me? Link to comment Share on other sites More sharing options...
dssenne Posted May 30, 2015 Author Share Posted May 30, 2015 Sorry, I was quoting Imdew's post #3. He said " If the engine is hot a single fans comes on, if you have the AC on, both fans should come on." Without jumping either the pressure switch or relay #2, the main fan won't turn on. But either way, the sub fan never comes on. If the AC system was not working because of incorrect pressure, could this cause the main fan to not work? Link to comment Share on other sites More sharing options...
Cougar Posted May 30, 2015 Share Posted May 30, 2015 Okay, I see what you mean now. Since the test plugs didn't work this may be a clue to the real issue. I suggest you ground the wire going to the ECU that controls the Main Fan to see if that works. If it does then you should find out why the ECU isn't working correctly. I assume you have first already checked that all the fuses in both panels are passing power through them using a test light or meter. Link to comment Share on other sites More sharing options...
dssenne Posted May 31, 2015 Author Share Posted May 31, 2015 Yes, I did check the fuses and all are ok. I went back and checked the voltage on the relays (arrows pointing to the terminals) On the first three relays I got 12V but on the 4th (A/C relay?), I go nothing. Don't know if this means anything or not. When you suggest grounding the wire going to the ECU that controls the Main Fan, could you explain how I'd do that? I see the ECU under the dash (gold box), but I'm not sure what I should do. Link to comment Share on other sites More sharing options...
Cougar Posted May 31, 2015 Share Posted May 31, 2015 Sure, I'll explain it and it is very simple to do once you know which wire ties to the relay coil. Hopefully you have a wiring diagram to refer to that will show you which pin on the ECU the wire ties to. Once you have it you just take a jumper wire that is connected to a good ground point and connect the other end of the jumper to the pin going to the relay coil. You can leave the connector to ECU in place while you do that. It may help to use something like a pin to stick into the backside of the connector to make contact to the jumper wire and the connector pin. You could also stick the pin through the wire insulation and make connection to the wire that way but that leaves a hole in the insulation. Dabbing some silicon glue over the hole would seal it up. If everything with the Main Fan circuit is okay, and you seem to have proved that already, the fan should turn on when you ground the pin. Other things you have done seem to indicate there is something going on within the ECU or the power to it. Link to comment Share on other sites More sharing options...
dssenne Posted May 31, 2015 Author Share Posted May 31, 2015 Cougar, thanks a lot for taking the time to respond to my posts. I really appreciate it. I do have a fsm so hopefully I'll be able to find the right pins in that. The section on the Radiator Fan shows a connection from the ECU at pin "d17" to FB-14 which says "To Power Supply Routing". When you say "relay coil" are you referring to the relays that I showed in the pictures above? Link to comment Share on other sites More sharing options...
Cougar Posted May 31, 2015 Share Posted May 31, 2015 Glad to help. For some reason the jpg images are not working. The relays you showed are the ones I am referring to and one of them is for the Main Fan. We are working with the coil lead of that relay that ties to the ECU and not the relay switch contacts. The coil lead of that relay going back to the ECU is what you need to tie to ground. The other side of the relay coil wire will tie to power somewhere, perhaps to fuse FB-14 also. Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted May 31, 2015 Share Posted May 31, 2015 sure you changed the right temp sensor? the one with 2 wires? Link to comment Share on other sites More sharing options...
dssenne Posted May 31, 2015 Author Share Posted May 31, 2015 Yes, it was the one with two wires. Not the one for the temp. gauge. Link to comment Share on other sites More sharing options...
dssenne Posted May 31, 2015 Author Share Posted May 31, 2015 Ok, now I'm really confused... The fsm shows the ECU as having four plugs with 22, 12, 16 and 26 pins. It looks like the pin for the m But my ECU only has three plugs with 16, 12 and 20 pins! Since the pins aren't labeled and my ECU doesn't match the schematic, I don't have a clue which pin to check! Link to comment Share on other sites More sharing options...
dssenne Posted June 1, 2015 Author Share Posted June 1, 2015 Well, I feel like an idiot! From doing some more google searching, it looks like the last image I posted is the transmission control unit, not the ECU. A post I read said that the ECU is located under the carpet on the passenger side. I'm going to check that out tonight. Link to comment Share on other sites More sharing options...
Fairtax4me Posted June 1, 2015 Share Posted June 1, 2015 Connect the green test plugs and turn the key ON. See if the fans cycle. Low-high-off in 1 second Intervals. The A/C compressor and fan are also not working, The blower fan inside the car doesn't work? Link to comment Share on other sites More sharing options...
dssenne Posted June 1, 2015 Author Share Posted June 1, 2015 The blower fan inside works fine, I meant the AC fan under the hood on the passenger side. Link to comment Share on other sites More sharing options...
dssenne Posted June 2, 2015 Author Share Posted June 2, 2015 Sure, I'll explain it and it is very simple to do once you know which wire ties to the relay coil. Hopefully you have a wiring diagram to refer to that will show you which pin on the ECU the wire ties to. Once you have it you just take a jumper wire that is connected to a good ground point and connect the other end of the jumper to the pin going to the relay coil. You can leave the connector to ECU in place while you do that. It may help to use something like a pin to stick into the backside of the connector to make contact to the jumper wire and the connector pin. You could also stick the pin through the wire insulation and make connection to the wire that way but that leaves a hole in the insulation. Dabbing some silicon glue over the hole would seal it up. If everything with the Main Fan circuit is okay, and you seem to have proved that already, the fan should turn on when you ground the pin. Other things you have done seem to indicate there is something going on within the ECU or the power to it. Well I finally found the ECU. Not easy to get to the right pin (d17). Anyway, when I grounded the pin for the main fan, sure enough the fan turns on. So, what direction does this point me in? Since I made the fan turn on by grounding pin d17, does this mean that the ECU controls the fan by grounding or "un-grounding" it? If that's true, is there some sensor(s) that tells the ECU when to do this? I replaced the water temp sensor, thinking that was it, but that didn't fix it. I replaced the thermostat, in case it was the problem, but no luck with that either. Is there something else in the circuit that tells the ECU to turn the fan on? Link to comment Share on other sites More sharing options...
Fairtax4me Posted June 2, 2015 Share Posted June 2, 2015 Did you put the ECU in test mode? Need to do this to see if the ECU is circuit is working properly. ECU grounds the relay to engage the fan. If it works in test mode the problem is sensor related. If it doesn't work the ECU needs to be replaced. Link to comment Share on other sites More sharing options...
dssenne Posted June 2, 2015 Author Share Posted June 2, 2015 Did you put the ECU in test mode? Need to do this to see if the ECU is circuit is working properly. ECU grounds the relay to engage the fan. If it works in test mode the problem is sensor related. If it doesn't work the ECU needs to be replaced. Do you mean connecting the two black connectors, below and to the left of the steering column? I did, and I got several codes, though none of them seem related to my problem of the fan not working. The codes I got were: 11 - crank sensor 22 - knock sensor 24 - air control valve 33 - speed sensor 35 - canister purge solenoid valve 42 - idle switch When I put the ECU in test mode, the fan didn't turn on. Though when I followed Cougars instructions for grounding the connector for the fan at the ECU, it did turn on. Link to comment Share on other sites More sharing options...
Fairtax4me Posted June 2, 2015 Share Posted June 2, 2015 Green connectors are test mode. Black are for codes. Link to comment Share on other sites More sharing options...
dssenne Posted June 2, 2015 Author Share Posted June 2, 2015 I tried the green connectors, but no response from the fan. Guess I'll see how much a used ECU is. Link to comment Share on other sites More sharing options...
dssenne Posted June 2, 2015 Author Share Posted June 2, 2015 Thanks to all who responded! Link to comment Share on other sites More sharing options...
dssenne Posted June 9, 2015 Author Share Posted June 9, 2015 Bought an ECU from AA Autoparts in Little Rock for $80 including shipping. Put it in tonight and now my fan works! Link to comment Share on other sites More sharing options...
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