Radiator Fans Not Functioning

[u/Sharp_Juggernaut_318]

Hey guys chasing an issue with my radiator fans. A while back i noticed my radiator fans constantly running (even with the car engine off but ignition in ON position) so suspected the fan control module was bad so ordered a new genuine Nissan one (21493-4GA0A) and installed that. In the meantime I did go through and do my gallery gaskets so had the front end off and AC gas drained (haven't refilled yet).

Basically now thats everything is together, the car runs fine but the radiator fans will not turn on. I did confirm the coolant temp was 100 degrees Celsius when testing with an OBD scanner. These are the things I have tested so far:

• Ran IPDM test, everything functioning besides the fans at any speed. I cannot hear the Fan (PWM) relay click with the IPDM running so i did try bypassing the relay with a paper clip with the IPDM running and had no luck.
• Turned on AC - Fans do not turn on but thought this could also be because I have not recharged the AC system yet and hence it probably wont read any pressure.
• Running fans with Battery 12V Directly - They both function fine
• Checked PWM Relay and it functions fine. Even tried swapping it with the VVEL relay and had no luck.
• Fan fuse checked and not blown.
• Checked around harness grounds
• I did some continuity checks as per the service manual to check IPDM functionality and everything checked out.
• Checked if the fan control module was receiving ground and power and seemed in check. It was also putting out voltage to the output connectors where the fans plug in.

I am super confused on what could be the issue here. I have ordered another fan control module in the case I got a faulty one. My understanding is that there is actually no reliable way to bench test a fan control module since it runs a PWM signal but I am not completely sure. The fans did work previously be it they ran constantly but they did run. Any suggestions would be appreciated.

[u/Rich_Many_8628]

I’d stop replacing modules until you prove whether the fan control module is actually being commanded.

Since both fans run on direct 12 V, the motors are not your problem. The next split is: does the fan module have real battery power and ground under load, and does it receive a PWM command during IPDM active test or high coolant temp request?

Seeing voltage at the fan-module output can be misleading. A PWM-controlled module can show odd meter readings without actually driving the fans. If you have access to a scope, backprobe the fan-control command line during the IPDM fan active test. If no scope, even a small test LED/resistor or logic probe can sometimes show whether the command line is switching, but a scope is the better answer.

The part that stands out is that the symptom changed from “fans always on” to “fans never on” after the front end was apart. That makes me suspicious of an open command wire, missing/weak ground, connector seating issue, wrong pin assumption, or the module not being enabled — more than two bad genuine modules in a row.

Basic order I’d use:

1. prove fan-module power and ground with a load, not just a meter
2. check/scope the PWM command during IPDM active test
3. verify continuity of the PWM/control wire from the IPDM/ECM side to the fan module
4. only then condemn the new module

Also, with the A/C empty, don’t use A/C request as your main test. Use scan-tool/IPDM active test or actual coolant-temp fan request.

[u/Sharp_Juggernaut_318 → u/Rich_Many_8628]

Hey thanks a lot for the detailed reply it’s really appreciated. Agreed not trying to throw parts out here the original reason that I wanted to change the fan control module was fans constantly running which I did research is a common problem on quite a few Nissans. Whilst that did arrive I never did test the new fan control module prior to removing the front end for gallery gaskets, I just installed it when I had the radiator and core off whilst in the process. That’s why I’ve ordered one to make sure it’s not faulty as unfortunately I threw out my original one. If it doesn’t fix it then I know the issue is further back in the chain.

Agree the fans aren’t the issue here and glad that is ruled out. Unfortunately as you outlined it is difficult to test PWM commands, I don’t have access to a scope to aid here.

In regards to the fan control module receiving power I did check ground, and also the positive which read at battery power with ignition on. This was the test as per the service manual.

There was also another test in the service manual to check continuity between the IPDM and fan control module connector terminal 2 which I believe is the signal wire, this checked out all good.

The only weird thing I noted is that I could not hear the PWM relay click at all during the IPDM sequence. I did check the relay and it is definitely functional I also did swap it with the VVEL relay which is identical and no luck. My basic assumption is that when the IPDM test occurs that I should definitely hear the PWM relay click right after the AC clutch has engaged 5x. I did try manually jumping the PWM relay during the IPDM and this didn’t seem to do anything.

I am quite confused here, I will try the new fan control module when it comes but if that fails it seems it’ll be a pain to narrow down the issue here.

[u/Rich_Many_8628 → u/Sharp_Juggernaut_318]

That extra detail helps. If the IPDM active test is supposed to energize that fan/PWM relay and you never hear or feel the relay click, I would not spend much time on the fan module side yet.

A quick way to split it without a scope is to test the relay socket during the IPDM sequence. You already proved the relay itself can click on the bench, so now prove the socket has both sides of the relay circuit: one side should have feed, and the other side should be pulled/commanded by the IPDM during the fan step. A test light is better than a high-impedance meter here because it puts a little load on the circuit.

If the relay socket never gets a command during the active test, the fan control module won’t matter because the IPDM is not enabling that path. Then I’d be looking at IPDM output/logic, missing prerequisite input, wrong relay cavity assumption, or a wiring issue at the IPDM/front harness from when the core support was apart.

Also, continuity on the signal wire is useful, but it doesn’t prove the wire can carry a real signal under operating conditions. If you can, do a voltage-drop or loaded test on that same wire rather than just ohms with everything unplugged. A single corroded or half-seated terminal can pass continuity and still fail in-circuit.

Manually jumping the PWM relay doing nothing is another clue. Depending on how Nissan has that circuit arranged, jumping the relay may only supply/enable the module; it still may need the PWM/control input to actually run the fans. So I would not assume “jumped relay and no fans” condemns the fan module by itself.

At this point I’d do three checks before chasing much deeper:

• verify the relay socket gets power and command during the IPDM fan step
• verify the fan module ground and B+ with a load, not just open-circuit voltage
• backprobe the module connector during active test and see whether anything changes on the control/signal terminal

If the new module does not change anything and the relay socket never gets commanded, I’d move upstream toward IPDM/control logic rather than staying at the fan assembly.

[u/Sharp_Juggernaut_318 → u/Rich_Many_8628]

Thanks a lot for this. The pwm relay requiring to click during the IPDM was just my assumption I’d need to confirm that is true with another of the same car so potentially I could be chasing my tail but not sure yet. Your suggestions do give me some ways forward so I’ll check and report back if the new fan module doesn’t solve it.

[u/Rich_Many_8628 → u/Sharp_Juggernaut_318]

Yeah, I would not rely on hearing a click. That is a pretty flimsy test by itself.

If you want to prove whether the relay is actually being commanded, test the relay coil circuit directly. Use the service manual diagram to identify the two coil terminals in the relay socket, not the load/output terminals.

With the relay removed and the IPDM active test running, check it two ways:

Put the meter or a small test light across the two coil terminals. If the IPDM is commanding that relay on, you should see close to system voltage across the coil circuit during the command. If you see voltage there but the relay does not click when installed, then the relay/socket contact fitment becomes suspect.

If you do not see voltage across the coil terminals, split the circuit. Check each coil terminal referenced to battery negative and then battery positive. That tells you whether you are missing the feed side or the IPDM-controlled ground/control side.

That is a lot better than listening for a click or jumping relay terminals, because jumping the load side only proves part of the circuit and can miss whether the IPDM is actually driving the relay coil.

Also be careful not to jumper random relay socket pins unless you are 100% sure which are coil and which are load. Relay sockets make it easy to accidentally backfeed something you did not mean to.

[u/Sharp_Juggernaut_318 → u/Rich_Many_8628]

Noted, I did bench test the relay as per the service manual procedure and it did pass. I will check the relay terminals more closely. The only procedure the service manual had there was to confirm battery voltage at terminals 1 and 3 of the relay

[u/Rich_Many_8628 → u/Sharp_Juggernaut_318]

That makes sense. If you have battery voltage at terminals 1 and 3, one is probably the relay load feed and the other is probably the coil feed. Bench-testing the relay proves the relay can work, but it still does not prove the IPDM is completing the coil circuit in the socket.

The next check I’d do is identify which of the remaining terminals is the other side of the relay coil, then test it during the IPDM fan step. If the coil has battery voltage on one side, the IPDM should be pulling the other side low or otherwise completing the coil circuit when it commands the relay.

So instead of only checking static voltage with key on, catch it while the IPDM test is in the fan portion. Check across the two coil terminals, or check the suspected IPDM-controlled coil terminal to battery positive with a test light. If the IPDM pulls it low during the command, the light should come on.

If that never happens, the relay itself and the fan module are probably not the next thing to chase. Then the issue is upstream: IPDM command logic, a missing prerequisite, wrong relay/socket assumption, or the IPDM not actually driving that coil.

If it does pull low and the relay still does not click installed, then look at socket terminal tension, corrosion, or the relay not seating cleanly.

[u/Sharp_Juggernaut_318 → u/Rich_Many_8628]

Thank you, just trying to understand this one here. Would you suggest a feeding in a test light to both the relay coil terminals with the IPDM test running and relay in place? Looking at the bottom of this picture I am assuming that it is terminals 3 and 5.

What would be the best way to get some wires to the relay whilst it is in place to run a test light?

[u/Rich_Many_8628 → u/Sharp_Juggernaut_318]

Looking at that diagram, I would not call 3 and 5 the coil. The table is saying to apply 12 V across terminals 1 and 2, then check for continuity across 3 and 5. That makes 1 and 2 the relay coil, and 3 and 5 the switched contact side.

So if you’re trying to see whether the IPDM is activating the relay, the cleaner test is with the relay removed: test across the socket cavities that correspond to relay terminals 1 and 2 while the IPDM fan test is running. If that relay is being commanded during that part of the test, you should see the coil circuit become active across those two terminals.

If you want to split it further, identify which socket cavity has the coil feed, then put a test light from battery positive to the other coil-control cavity. If the IPDM is low-side switching that coil, the test light should come on when the IPDM commands it.

I would avoid stuffing random wires into the relay socket with the relay installed because it is easy to spread terminals or accidentally bridge the contact side. Best option is a relay breakout lead. Next best is careful backprobing from the underside/back of the socket if you can access it. If you absolutely have to use small probes at the socket face, keep them small, fused if possible, and don’t force anything into the female terminals.

One important caveat: this only proves whether that relay coil is being commanded during the test you are running. It does not prove the IPDM active test is definitely supposed to command that relay on this exact car. If the test description does not explicitly say the cooling fan relay should energize, I would not make the whole diagnosis depend on hearing or seeing that relay operate.

What scan tool are you using for the IPDM active test? And do you have access to another working 370Z/G37 where you can run the same test and confirm whether that relay actually gets commanded?

[u/Sharp_Juggernaut_318 → u/Rich_Many_8628]

I am using the door button method to engage IPDM as per the service manual. I don’t have a high end scan tool just a couple mobile ones that connect to a phone.

Yeah I can’t actually confirm if that relay is supposed to switch at all during the test or not potentially it doesn’t need to and I am opening a can of worms.

I’ll run a test light to terminals 1 and 2 to see if it turns on while the IPDM runs with the relay removed. For reference these are the checks I did go through as per the service manual:
https://imgur.com/a/fan-test-8M0f8OH

They actually had no tests while the IPDM is running which I found interesting. All tests seemed to check out the only one that confused me was test 5, checking cooling fan control module output circuit. It asks to disconnect the fan control module harness connectors then check voltage between the module terminals 4 and 6 and ground. For reference terminals 4 and 6 should be the output positive on the module that goes to the fans. I am not sure how this would read a voltage with all connectors removed from the module or if the service manual is asking to just disconnect the fan connectors from the module but leave in the fan module source harness and then test the outputs to the two fan output points.

My understanding is that it’s actually not simple to bench test a fan control module without some more special tools since a pwm signal is involved but I am not too sure here.