11Budlite Posted June 16, 2022 Share Posted June 16, 2022 I'm trying to determine why my cooling fan hasn't switched on. Originally, the sensor wire for the temp gauge and the gas gauge were switched so I was getting some funky readings on those two gauges. After fixing that issue, I drove it in the colder months and didn't expect the cooling fan to come on so wasn't too concerned. Come spring time and some warmer weather and the cooling fan still hasn't come on. I've bled all the air out of the system again, installed a different gauge with better resolution than the stock Caterham gauge, both upper and lower hoses are getting hot, all wiring to the ECU temp sender/gauge sender/cooling fan appear to be okay, and the cooling fan runs when I jump it. I now have the scuttle off and have better access to the wiring and relays. I've attached 3 photos of the the relays I can find. One is a 4-relay block attached to the bulkhead, 1 is cable-tied in front of the speedo, and 1 is cable-tied in front of the tach. From memory the wire to the cooling fan is black with a green tracer. I don't see that wire coming from any of the relays. Does anyone know what relay is the cooling fan relay? Link to comment Share on other sites More sharing options...
MV8 Posted June 16, 2022 Share Posted June 16, 2022 To save some effort, request from Caterham, a pdf of the handbook that covers 2019 models and a schematic or factory service manual covering the model, which would include the schematics. Another option is to pull and reinstall each relay until you find one that doesn't seem to do anything. Same situ for the fuses. Usually for a dc fan on older equipment, there is a separate, single terminal, coolant switch but there are many ways to do it. The relay may control the positive or the negative lead to the fan. If you feel comfortable and capable with a dvm, paper clips, and a jumper lead (DIY assembly of alligator clips on a few feet of 14-18ga copper stranded/primary wire), I can tell you how to find the problem without splitting the harness open. Link to comment Share on other sites More sharing options...
JohnCh Posted June 16, 2022 Share Posted June 16, 2022 Check out the Caterham Build & User Guide folder in the Downloads section. Wiring diagrams are included in some of those PDFs. -John Link to comment Share on other sites More sharing options...
11Budlite Posted June 16, 2022 Author Share Posted June 16, 2022 Thanks guys. I have an owners manual, build manual(s), and a Sigma wiring diagram. The wiring diagram I have shows 7 relays and I can only find 6 on my car. From what I can tell, there is an ECU temp sensor in the back of the cyl head that sends a variable temp signal to the ECU, which sends a signal to the relay at the correct temp, which in turn will turn on the cooling fan. I believe the signal from the ECU is switched ground. I do have the EasiMap cable setup coming from SBD to help diagnose the issue. It's very frustrating because the engine is brand new and I don't want it to overheat. Link to comment Share on other sites More sharing options...
MV8 Posted June 16, 2022 Share Posted June 16, 2022 Assuming you have the right diagram, ground a clip to the chassis, unplug the ecu, find the right terminal, then touch to ground to see if the relay clicks and/or the fan comes on. Another option is to use your handbook to find the right fuse, pull it, find the side that still has voltage, probe the other side with the dvm set to beep continuity, then back probe the relays. Care to share the diagram? Is it the right one for your car? Link to comment Share on other sites More sharing options...
MV8 Posted June 16, 2022 Share Posted June 16, 2022 Once you find the right parts, we can figure out why. Link to comment Share on other sites More sharing options...
11Budlite Posted June 16, 2022 Author Share Posted June 16, 2022 If I figure out which is the correct relay I'm sure I could figure it out. When I get home I'll get access to the ECU wiring/plug and see what I can find there. Pg 156-160 of this manual is what I've been using: Link to comment Share on other sites More sharing options...
MV8 Posted June 16, 2022 Share Posted June 16, 2022 The "schematic" looks like the use is to help customers install a harness and doesn't match your relay config/fuse block like you've said. It does show the fan switch in the radiator and matching connections at the fan and relay. Not really a schematic and also the diagrams are cut-off. The correct owners handbook should show the location of the relay. Do you have a temp sensor in the radiator or is it blocked off/plugged? To find the fan relay, you could disconnect the battery, unplug the fan and back probe for continuity to a relay terminal but you may need the long diy jumper for the dvm leads to reach. What does the fuse panel look like? Link to comment Share on other sites More sharing options...
11Budlite Posted June 16, 2022 Author Share Posted June 16, 2022 There's no fan switch in the radiator. There's an ECU temp sensor in the back of the cylinder head and a coolant temp gauge sensor in the "submarine" right below it. The ECU signals when to turn the fan on. I believe it's ECU pin 33. The owners manual has the following relays listed for models 270/310/Academy: 1: Ignition 2: Lights 3: Indicator 4: Hazard 5: Starter 6: Fuel Pump 7: Cooling Fan I've checked for continuity between the the cooling fan black/green wire to the '87' terminal of the relays and haven't found anything yet. Still only see 6 relays. I've attached a photo of the fuse panel and the ECU temp sensor. Link to comment Share on other sites More sharing options...
MV8 Posted June 16, 2022 Share Posted June 16, 2022 What are you jumping for the fan to turn (+,-, which wire)? Is it turning the right direction? I'll guess that blk/grn is being jumpered positive and blk is a constant ground. The correct owners handbook should also list an associated fuse that can help you find the relay. What did you find with the ecu pin 33? Why is the engine new? Overheated? I guess you are the second owner? A little back story please. Link to comment Share on other sites More sharing options...
11Budlite Posted June 16, 2022 Author Share Posted June 16, 2022 (edited) I jumped the black/green wire with a fused wire directly from the pos battery terminal. Black wire at the cooling fan connector is ground. It's turning the correct direction. There is no fuse labeled 'cooling fan' for the 270/310 model in the manual, but there is a 'cooling fan' fuse for the 275/280 model listed that's a 15a fuse. I checked all of the fuses and none of them are blown. It's a brand new Caterham kit I just finished in the fall of 2021. The cooling fan has never come on unless I jumped it. Edited June 16, 2022 by 11Budlite Link to comment Share on other sites More sharing options...
MV8 Posted June 17, 2022 Share Posted June 17, 2022 The checks (with the battery disconnected) should include all relay terminals and the tach and speedo secured relays, then the ecu connectors (ecu unplugged), all the fuse terminals (unless you already checked that all the fuses have power always or in run and not just if they are blown). If all that fails to find continuity (ignore color codes), you can add a compact system at the fan with new wire, a sensor and relay with an inline 10-12ga ato fuse holder to the alt stud or open the harness covering to find waldo and retape. You might start near where it should be with the other relays and fuses. Sounds like they cut out the typical circuit and forgot to add it back in for the ecu control. Your pics are very clear but maybe pull back some for the overall area so we could broaden our focus. Might help. Link to comment Share on other sites More sharing options...
MV8 Posted June 17, 2022 Share Posted June 17, 2022 Also, with the compact setup off the alt, you could run one additional wire along the harness for fan operation only in RUN, jumpering off the main relay 87. I doubt the fan pulls more than 15 amps. You might try tugging on the blk/grn a bit. It may only be a foot long or be a foot short of the normal bank of relays. Link to comment Share on other sites More sharing options...
MV8 Posted June 18, 2022 Share Posted June 18, 2022 While the arrangement is not the same, it looks like a 310 (duratec) has a total of six relays and a 20 amp fuse for the fan. Link to comment Share on other sites More sharing options...
11Budlite Posted June 20, 2022 Author Share Posted June 20, 2022 Thanks for your help MV8. 1 Link to comment Share on other sites More sharing options...
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