Thermostat does not open to turn on the radiator fan

MALLYBOY

MEMBER
2007 HONDA CRV
2.4L
4 CYL
4WD
AUTOMATIC
95,000 MILES

This vehicle had an ECM problem in that it did not start. Then I diagnose and pick P0685:PGM-FI relay control. Then I traced it and noticed that ECM control side was faulty. Then I replaced and programmed it and the fault code was gone. But the radiator fan cannot turn on except when you turn on AC the radiator fan comes on. Then I diagnosed it and pick P0128: thermostat. Then I replace the thermostat and start the vehicle. I monitored the coolant temperature until it reached 90°C but the fan did not turn on. At this point I am confused to say if the thermostat did not open to allow coolant to flow through the engine and engine coolant tells the ECM to trigger the cooling fan. Help please.

5 Replies

KASEKENNY

MECHANIC
18,907 POSTS

Just to clarify, when you replaced the PCM was this an issue with the old PCM?

Did you use a new PCM or a used one?

The way this works is the temperature sensor tells the PCM what the engine temperature is and that will determine if the fan needs to be on.

Have you removed the thermostat and put it in boiling water to find out if it is opening? It sounds like if you replaced the thermostat that this is not the issue and that it may be opening but the temperature sensor is either faulty or the PCM that you replaced as an issue.

The quickest way to test this is to put the old PCM in (which will cause the other issue to come back) and see if the fans come on. If they do, then you know the PCM is the issue.

https://www.2carpros.com/articles/how-to-check-an-electrical-relay-and-wiring-control-circuit

However, if the temperature sensor is working and the thermostat is in fact opening in boiling water then we need to check the relays to find out if they are the issue or we have another PCM issue.

We need to check the purple wire from the radiator fan relay to the PCM and see if the PCM is grounding this terminal. If it is then the PCM is commanding it on, it is just not coming on. If the fan works when the A/C is on, then I suspect we have a PCM issue.

Let's start with this info and we can go from there.

Thanks

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Thursday, May 12th, 2022 AT 7:08 PM

MALLYBOY

MEMBER
300 POSTS

The problem had been solved. I replaced used PCM and Used thermostat, from the description of how the thermostat works, it stated that it begins to open at 70°C and fully open at 90°C. But because the thermostat has been used, it opens at 101°C and closes at 98°C. I allow the vehicle to be idling and I was using live data to monitor the temperature, immediately it reaches 100°C and at 101°C the fan turns "on" and turn off at 98°C.

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Saturday, May 14th, 2022 AT 12:23 PM

KASEKENNY

MECHANIC
18,907 POSTS

That is great. Thanks for following up with us and letting us know what repaired.

Talk to you next time.

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Saturday, May 14th, 2022 AT 6:25 PM

MALLYBOY

MEMBER
300 POSTS

There's another issue on this vehicle, when you turn ignition on, the PGM-FI Relay, ECTS, PGM-FI SUB-Relay, Fuel Pump Relay will be making clicking sound and oil warning lamp and key light blinking together with the relays clicking sound. I put old ECM, battery, oil and key light did not come on. I got another ECM, and it was doing the same. What could be the cause of this? I attached the video below.

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